On this tutorial I’ll share how I take advantage of Blackbox logs to tune filters and PID on a Betaflight FPV Drone. I shall be utilizing PIDToolBox as the first software for filter and PID tuning, with Blackbox Explorer because the secondary software for Feedforward and common troubleshooting.
Disclaimer: This information is supposed for informational functions solely. The writer holds no accountability for damages ensuing from actions taken by the readers.
Blackbox is just not a should on the subject of tuning as defined on this information, however Blackbox provides you the complete perception into what’s actually occurring with the drone and means that you can unleash its full potential. Issues like noise filtering and tiny overshoots you possibly can solely see in Blackbox. In case you are a perfectionist or simply somebody who wish to tinker, that is going to be the tutorial for you.
In case you are new to Blackbox, make certain to take a look at the Blackbox for rookies tutorial.
I spent over 200 hours making this 8000-word tutorial! In case you discover my content material helpful, please contemplate supporting my work.
Getting Began
Tuning objectives
Utilizing Blackbox to tune our FPV drone, we wish to obtain two major objectives:
- Simpler use of filters: use as little filtering as potential to attenuate delay, however simply sufficient to maintain the noise right down to a suitable stage
- Optimized PID positive aspects and associated settings to get our drone to fly extra exactly and responsively
Primary configurations
0. {Hardware} Guidelines
- Select an FC stack that comes with rubber grommets (aka gummies), gentle mounting is nice for each sturdiness and noise efficiency (vibration dampening).
- Use steel screws for the FC stack, keep away from nylon/plastic screws/standoffs/spacers as they’re straightforward to interrupt and extra prone to create vibrations. In case you want spacers, use the gentle silicone ones. Utilizing lighter titanium screws can save just a few grams (see submit).
- Locking the stack screws firmly in place with a steel nut earlier than mounting the 4in1 ESC. In case your body have pressed insert nuts then there’s no want so as to add one other nut. It will stop the stack screws from wiggling and creating vibrations. Tighten them by hand first, then give a closing squeeze with the wrench/screwdriver.
To safe the entire FC stack, you need to use 4 plastic nuts. Tighten the nuts by hand, in order that the gummies are usually not excessively crushed, this enables the soft-mount to work successfully.
1. Blackbox Recording Settings
Choose the next settings within the Blackbox Configuration:
- Logging gadget: Onboard Flash or SD Card
- Logging charge: 2KHz (or 1.6KH for BMI270 Gyro)
- Debug mode: GYRO_SCALED (which information unfiltered gyro sign)
- Knowledge included: If you wish to avoid wasting area to file for longer, you possibly can de-select knowledge that’s no wanted for PID/filter tuning, reminiscent of Altitude, GPS and Magnetometer. In any other case simply depart it at default.
2. Disable ADC filter in your OpenTX/EdgeTX radio (System->{Hardware}). It will scale back latency.
3. ESC settings:
I’ve a submit explaining the greatest BLHeli32 settings. Right here’s the abstract (for five″ drones):
For BLHeli_32 ESC:
- Rampup Energy 30%
- Motor timing 24
- PWM Frequency: Setting LOW and HIGH to fastened 24KHz or 48KHz. 48KHz is usually the most secure choice on the subject of gyro noise, it makes your quad smoother and simpler to tune. Nevertheless, 24Khz provides higher braking energy which is healthier for prop wash dealing with and responsiveness, however there’s a better threat of vibration.
For BLHeli_S ESC, flashing Bluejay is a should, as a result of it permits bi-directional DShot, which is required for RPM filter and Dynamic Idle. I’ve a information on how you can flash it right here: https://oscarliang.com/bluejay-blheli-s/
3. Flash the newest model of Betaflight firmware to your flight controller and depart PID/filter settings at default. Allow Skilled Mode in Betaflight Configurator, this gives you all of the accessible sliders and choices on the PID Tuning web page.
- DShot300 for 4KHz or 3.2KHz Loop Frequency
- DShot600 for 8KHz Loop Frequency
4. Within the Motors tab, allow Bi-directional DShot.
Virtually all fashionable ESC help Bi-directional DShot. I’ve a tutorial on how you can allow RPM filter. For BLHeli_32 ESC it really works out of the field, however in case you have BLHeli_S ESC, it is advisable flash Bluejay firmware (tutorial) first.
To verify if Bi-directional DShot is working correctly, run the motors within the Motors tab (with out propellers!) and see if the error charge (E) stays at 0% . If this isn’t the case, strive once more with a slower DShot protocol reminiscent of DShot300 and even DShot150. If none of those protocols provide you with 0% error, you then would possibly simply need to disable Bi-directional DShot.
After getting Bi-directional DShot enabled, you possibly can then allow RPM filter, that is in all probability the most effective filter in Betaflight.
5. Load the suitable RC_Link preset.
Totally different RC hyperlinks require particular RC smoothing and feedforward configurations as a result of completely different packet charge and packet interval with a view to keep away from issues with Feedforward. My favorite RC hyperlink for the time being is ExpressLRS, take a look at what radio gear I take advantage of right here.
By loading the appropriate RC_Link preset, Betaflight will apply all the required config for you robotically. Don’t neglect there are just a few extra choices to select earlier than loading the preset, particularly flying type, for most individuals it could be Freestyle.
In case you are utilizing Crossfire, it’s greatest to lock the packet charge to both 50Hz (longer vary however greater latency) or 150Hz (decrease latency however much less vary). You are able to do this within the TBS Agent Lite LUA script.
6. Decrease TPA
Within the PID tuning tab, set TPA break level from 1350 to 1750, that is the throttle place when TPA begin to work. It will keep away from TPA masking all of the oscillation points at low/mid throttle throughout tuning. We’ll tremendous tune TPA on the finish if we now have oscillation points at excessive throttle vary, however usually I’d decrease the usage of TPA at any time when I can.
Find out how to use PIDToolBox and Blackbox Explorer?
I shall be utilizing each PIDToolBox (PTB) and Blackbox Explorer (BE) in my PID and filter tuning.
PIDToolBox shall be our major software, it’s by far probably the most highly effective Blackbox software accessible. It means that you can evaluate a number of logs aspect by aspect on the identical window, so you possibly can see the consequences of the modifications you made in an occasion. The Step Response software is tremendous easy and helpful for tuning PID. One other great point is the unit on the Y axis within the spectral analyzer (in decibel), which permit for extra correct and goal comparisons. PTB additionally tells you the estimated filter delays which is beneficial.
The principle draw back of PTB for my part is pace. It hundreds fairly a bit slower and it simply isn’t as intuitive to make use of as BE. That’s why I largely use BE if I solely have to take a look at one log, or for common troubleshooting as a result of it’s simply quicker to make use of. However for noise and filter tuning, PTB is certainly the way in which to go.
Filters Tuning
You will discover all of the filters in Betaflight within the PID Tuning tab. Don’t be intimidated by all of the settings, we’ll largely solely play with the inexperienced sections (RPM filter and Dynamic Notch), then alter the orange sections (Gyro and D Time period Lowpass Filters) utilizing the sliders. We received’t have to the touch the purple sections.
Additional studying: Study in regards to the several types of filter in Betaflight on this tutorial.
{Hardware} performs a giant half in how a lot filtering is required. For instance, a effectively designed body with out dangerous resonance points, a set of effectively balanced propellers, good high quality motors with clean bearing, all contribute to a clear quad that requires minimal filtering.
Performing flight for noise evaluation
Take off, fly ahead with as little throttle as potential and minimal yaw/pitch/roll stick inputs.
Carry out “throttle sweeps” – slowly ramp up throttle till it reaches 100% over 5-10 seconds. Vibration frequency attributable to the motors can change with throttle stage, this take a look at will present all of the vibrations throughout the entire throttle vary in addition to the place the body resonances are.
Repeat this 2-3 occasions, then land and disarm.
That is what a typical throttle sweep log would appear to be (see the underside bar for throttle modifications).
Understanding Gyro Frequency and Delay
Now open the “throttle sweeps” log in Blackbox Explorer, and click on on “Gyro_Scaled” (unfiltered gyro sign) in the best hand pane. It’s vital to take away the take off and touchdown components of the log (so these vibrations don’t throw our evaluation off) by urgent the keys “i” and “o”.
Right here’s a breakdown of the uncooked gyro sign frequency graph from a typical 5″ FPV Drone:
- Beneath 20Hz: drone flight actions
- Between 20Hz – 100Hz: propwash and oscillations attributable to suboptimal PID (e.g. trilling attributable to an excessive amount of D acquire), problematic ESC config and dangerous RC hyperlink associated settings and many others…
- Between 100Hz – 250Hz: body resonance or free components
- Increased than 250Hz: noise from motors and propellers, and harmonics
Every little thing under 20Hz is “good” drone movement reacting to the sticks.
Between 20Hz and 100Hz is the undesired vibrations reminiscent of oscillations and propwash. As a common rule of thumb, you wish to see little exercise on this frequency vary. Having some is regular however an excessive amount of means you could have an oscillation concern that must be addressed. Usually we attempt to keep away from filtering under 100Hz as a result of these are actual motions of the drone, that we both wish to work with or work in opposition to. Filtering on this low frequency vary can truly make issues worse as a result of it introduces great quantity of latency. Analyzing the spectra beneath 100Hz can provide you perception into vibration or mid throttle oscillation points, and the way effectively the copter is handing propwash.
We don’t care about something above 1000Hz as these have little impact on our drone, what we wish to deal with filtering is the noise between 100Hz and 1000Hz.
Maybe not intuitive, however over-filtering can truly trigger oscillation to point out up as noise within the sub-100Hz spectra. That’s as a result of filtering creates one thing referred to as part delay. When the quad tries to make a correction to the error, the response is simply too late attributable to delay and is definitely counter productive. It makes the error worse and creates a suggestions loop, so the drone begins to oscillate.
That’s why if we use much less filtering, noise points beneath 100Hz can typically truly get higher, as a result of latency is decreased and the quad can react quicker to right PID errors. Utilizing much less filtering additionally means that you can push PID positive aspects greater which makes your quad monitor setpoint higher and helps fight propwash.
You will discover out how a lot delay is added to the Gyro sign attributable to filtering, by plotting Gyro and Gyro_Scaled and measure the hole between them.
In PTB, it robotically estimates the delay attributable to gyro filtering and D-term filtering (see prime proper nook of the primary graph in second column).
Filter Technique
My common filter technique is to kill motor noise bands utilizing RPM filter, then crush out body resonances with dynamic notch filters, lastly scale back the ambient noise ground with Gyro and D-term lowpass filters. I shall be tuning filters on this order:
RPM Filter => Dynamic Notch Filter => Gyro Lowpass => D-term Lowpass
We wish as little filtering as potential to attenuate latency, however on the similar time to have sufficient filtering in order that we don’t burn our motors after we are flying residence with a bent prop. One can definitely play protected and apply extra filtering than wanted, however when over-filtering, the drone would really feel disconnected and gradual to react as a result of elevated delay. It makes propwash worse too. So there’s a steadiness we wish to try for.
Other than checking Blackbox logs, motor temperature is one other helpful dedication in filter tuning. When motors get too sizzling is normally an indicator of pushing the filtering too far.
Professional Tip: Sizzling motors – how sizzling is simply too sizzling?
As a common rule of thumb, for those who pinch the motor and might’t maintain your fingers on it quite a lot of seconds, meaning it’s too sizzling and you’re in all probability pushing your setting too aggressively.
How Clear is Your Construct?
Earlier than we start, you would possibly wish to verify in case you have a clear construct. Carry out throttle sweeps as earlier described.
Load the log in PIDToolBox, click on Spectral Analyzer. Choose simply “Gyro prefilt” (the uncooked unfiltered gyro sign, “Gyro” is the filtered sign), and hit Run.
On a clear 5″ quad, there must be little exercise between ~50Hz (the quad’s actions) and ~200Hz (motor vibration). You probably have numerous noise on this area, it might be electrical noise (maybe gyro enter energy is simply too noisy, or it requires additional capacitor on the ESC enter energy), or possibly mechanical (e.g. a wire is hitting the gyro). It could be more durable to get optimum filtering on this situation.
As prompt by the writer of PIDToolBox, it’s very best to have the general noise ground under -30dB above 50Hz. For D time period, it’s very best to have the general noise ground under -10dB. From wanting on the noise stage in these areas can actually inform how clean your quad flies. The noise stage has to do with how effectively the drone is constructed, how good the {hardware} high quality is, and typically you would possibly simply have a loud Gyro.
In case your quad is noisier than this (e.g. there’s a peak within the center above 0dB), then you have to extra filtering. It’s not the tip of the world, it simply means the latency shall be greater and also you received’t be capable to push PID positive aspects as excessive.
Tuning RPM filter
Motor noise is the principle supply of noise for FPV drones, and RPM filter is likely one of the best filters in Betaflight for tackling motor noise. On a clear construct, RPM filter and Dynamic Notch filters shall be doing a lot of the work, and we are able to disable many different filters to attenuate latency.
Let’s have a look at some examples of motor noise:
- Load the “Throttle Sweeps” log in PTB, click on Spectral Analyzer and click on “Freq x Throttle“.
- Beneath “Presets” choose “Gyro Prefilt, Gyro, Dterm Prefilt, Dterm” and hit Run. That is what I name “warmth maps”.
Let me clarify what we’re right here:
- Near 0Hz, the very shiny horizontal line on the backside (1) is the drone’s movement reacting to the sticks.
- Round 200Hz, the horizontal line (2) is the body resonance. Its frequency doesn’t change regardless the throttle place, but it surely’s the strongest the place it intersects with motor band.
- The diagonal line (3) is the basic motor noise band, normally the brightest, motor noise sometimes will increase in frequency with throttle stage.
- There are sometimes harmonics at multiples of the basic motor noise band. In our instance, (4) and (5) are the motor noise band harmonics, they are typically dimmer, typically onerous to identify. Attempt adjusting the size and see in the event that they present up extra clearly.
- Word that 2-blade propellers have a tendency to point out extra and stronger harmonics than 3-blade props.
We’ll use RPM filter to deal with these motor noise bands.
Tuning RPM filter principally means to optimize the variety of RPM harmonics used and set the very best potential “Min Frequency” based mostly on the beginning frequency of the motor band.
Fewer RPM harmonics and Increased min freq = much less filtering and fewer latency.
Click on the “Knowledge Cursor” software, and click on on the place the motor band begins, it is going to inform you the precise frequency. Affirm in roll/pitch/yaw graphs, and take the bottom frequency.
Right here’s an instance of me tuning my new Supply One V5 construct:
- On the left, is the default RPM filter: 3 Harmonics with min frequency of 100Hz
- On the best, 2 Harmonics with min frequency of 160Hz
By lowering one harmonics and lift the cutoff frequency, you possibly can maybe see extra unfiltered noise from the third motor harmonics.
Though it’s fairly weak, it may well nonetheless get amplified when it will get into D time period. Let’s verify the Dterm warmth map under on the best, as you possibly can see, a tiny little bit of gyro noise has change into fairly dangerous Dterm noise.
On this instance, it’s in all probability higher to have 3 harmonics in RPM filter.
The opposite factor you might need seen is a few noise round 116Hz left unfiltered as a result of we raised the min freq to 160Hz. To handle that, we now have to decrease Min Freq, i.e. round 20Hz under the noise frequency could be very best.
Right here’s a comparability of gyro sign after filtering utilizing 3 completely different settings:
- left: 2 harmonics 160Hz min freq
- mid: 3 harmonics 130Hz min freq
- proper: 3 harmonics 100Hz min freq
To crush out the motor bands, it appears we are able to’t actually scale back RPM filter from the default on this case. The default 3 harmonics and 100Hz min freq works the most effective for us on this instance.
RPM Crossfading
This superior function fades within the RPM filter power over a variety (form of like TPA), the default is sweet for many 5″ builds however it may be optimized particularly for bigger or smaller builds, because the motor noise would possibly begin greater or decrease in frequency, and also you would possibly want it to fade in additional rapidly or slowly is dependent upon the noise. This function is just accessible in CLI, for instance:
set rpm_filter_min_hz = 100 set rpm_filter_fade_range_hz = 50
This implies the RPM filter is efficient from 100Hz, however at minimal power, the filtering strengths will increase from 100hz and change into full power at 150hz.
Q Worth
Growing Q worth of a notch filter makes it extra centered on the focused frequency (narrower vary), additionally reduces latency. Once more, this superior setting is just accessible within the CLI, for instance:
set rpm_filter_q = 500
Default works effectively a lot of the occasions, however may be tremendous tuned by rising Q till motor noise is seen within the Filtered Gyro diagram, then again off. Don’t exceed 1000.
RPM Filtering Dimming
This enables particular person management of every RPM filter to focus on harmonics. For instance, when utilizing 3-blade propellers, the second harmonics is normally not very sturdy, however the third harmonics is. On this case you need to use extra filtering power on the third harmonics and fewer on the 2nd:
set rpm_filter_weights = 100, 0, 80
And when utilizing 2-blade propellers, the place 2nd harmonics is stronger than the third harmonics, you are able to do one thing like this:
set rpm_filter_weights = 100, 80, 0
You’ll be able to lower RPM filter weights much more so long as motor noise is just not seen within the filtered gyro diagram.
Tuning Dynamic Notch Filter
The dynamic notch filter suppresses sign peaks in gyro sign which might be largely vibrations from the body or different {hardware}, i.e. body resonance (carbon fibre may be surprisingly springy), antennas, GoPro in a TPU mount, and bent propellers.
When RPM filter is enabled, Betaflight will robotically scale back the quantity of Dynamic Notch filtering (fewer notch counts and better Q worth) as RPM filter will do a lot of the heavy lifting. You’ll be able to additional tune Dynamic notch based mostly by yourself setup.
Tuning Dynamic Notch Filter means to attenuate the notch depend, use the very best potential Q worth and maintain the min/max frequency as slim as potential. Fewer notches = much less filtering however decrease latency. Even higher, if body resonance isn’t very sturdy, you possibly can strive disabling this filter to avoid wasting filter delay.
Have a look at the warmth map and establish what number of body resonances there are to resolve what number of notches are wanted. You’ll be able to have as much as 5 notches however normally 1 or 2 must be sufficient until your drone is poorly constructed or in a very beat up situation. Particularly when you could have RPM filter enabled, 1 notch is normally sufficient to crush out body resonance. In case your quad can’t use RPM Filter, for instance on a tiny whoop, you possibly can attempt to allow Dynamic Notch Filter with 5 harmonics, Q issue 350 and Min Frequency at 100Hz as a place to begin, then tune it by working your approach up.
On this instance, there solely appears be to at least one body resonance round 210Hz (see the horizontal line that seems throughout the entire throttle vary).
The Q worth determines the width of the filter: Increased Q = narrower filter, much less filtering however decrease latency.
If the default Q of 500 is working effectively, strive 600 and even 700 (principally discover the very best Q worth that may nonetheless adequately management these resonances), however keep away from exceeding 1000. If after filtering you possibly can nonetheless see the body resonance noise, you would possibly want a decrease worth. Test Dterm heatmap to see the way it impacts D-term noise as effectively to resolve whether or not or not your Q worth can go greater.
Min/Max Frequency are the cut-off frequencies, it’s principally the efficient vary of the Dynamic Notch filter. Merely add 20-30Hz further vary to every aspect of the resonance.
I’d keep away from setting Min Frequency too excessive for security as bent props can create large resonance too. In case you crash and attempt to fly residence with a bent prop, the dynamic notch filter can actually assist to scale back the vibrations that may get into the D-term. We don’t know precisely the place that resonance goes to be, however having a wider frequency vary has a better likelihood of catching it. If the Dynamic Notch fails to catch these newly pop up resonances attributable to Min Frequency is ready too excessive, your motors can get sizzling and even burn in these conditions.
On this instance, I attempted to extend Q to 700 and set the min/max frequency to 160-230Hz, however Q is clearly too excessive I believe. There’s extra unfiltered noise, and it will get into Dterm and get amplified.
Lastly, once I set Q to 450, the noise is satisfactorily managed. Within the under graphs, on the left is Q=700, the best is Q=450. You’ll be able to verify Dterm heatmap once more to verify that is working effectively.
Tuning Gyro Lowpass Filter
Most often you possibly can simply flip off Gyro Lowpass 1 filter because it’s not wanted, take a look at fly aggressively for 30 seconds, and verify motor temperature to verify they aren’t sizzling earlier than continuing.
Then use the “Gyro Filter Multiplier” slider to scale back Gyro Lowpass 2 a few notches at a time. Transferring the slider to the best = shifting frequency up = lowering filtering = much less delay = higher prop wash dealing with and better PID positive aspects.
Right here I’ll evaluate the gyro frequency spectrum between Gyro Lowpass filter slider worth 1.0 (brown), 1.5 (purple) and a couple of.0 (orange).
The three strains virtually overlap one another, that counsel Gyro lowpass filter isn’t actually doing a lot and may be decreased. Apparently, for those who have a look at the noise within the sub-100Hz spectrum, it truly will get ever so barely higher with much less filtering, that echoes what we talked about earlier.
Essential:
- By no means disable Gyro Lowpass 2 filter for 2K/4K PID loop frequency attributable to anti-aliasing causes
- For 2K looptime, depart Gyro Lowpass 2 at 500Hz because the minimal
- For 4K you possibly can set Gyro Lowpass 2 so far as 1000Hz
- For 8K, you possibly can disable Gyro Lowpass 2 totally if noise isn’t a problem
Tuning D Time period Lowpass
D time period is way noisier than Gyro attributable to its delicate nature and noise will get amplified as frequency goes up, so be additional cautious and conservative when coping with D Time period filtering.
Attempt shifting the “D Time period Filter Multiplier” slider to the best a notch at a time and see how the drone responds in a 30-second take a look at flight (do some acro strikes), additionally verify motor temperature after touchdown. In the event that they get sizzling it’s best to return a notch or two.
I’d warn in opposition to going too aggressive with lowering D Time period filtering, depart some headroom for potential bent props throughout flight. Too little D Time period filtering and a broken propeller are the most effective mixture for decent/burned motors.
Right here’s a comparability between 1.0 (brown), 1.3 (purple) and 1.6 (orange) in D-term filtering slider positions. As you possibly can see much less filtering is clearly noisier for dterm, in contrast to Gyro lowpass.
In case you hear the motors getting tough (thrilling oscillation) as you scale back d-term filtering, it’s the rising noise under 100Hz (you possibly can verify the <100Hz graphs to verify). On this instance I’d in all probability keep under 1.3, possibly 1.2 and even simply 1.1 to be protected.
After you could have tuned PID positive aspects, it’s best to come again and verify once more if D Time period filtering may be optimized.
If the D Time period traces are very noisy, one or two clicks extra filtering on the slider could assist. If the D time period hint could be very clear, you possibly can maybe scale back filtering a bit extra (if motors are usually not sizzling). See under graphs, the left has a loud D time period hint, the best is way cleaner.
Essential: NEVER disable D-Time period lowpass filters fully, you’ll burn your motors.
Gyro/D Time period Notch Filters
There’s no want to the touch Gyro Notch Filter and D Time period Notch Filter, these are static notch filters which have change into legacy since they’ve been changed by RPM filter and dynamic notch filters. So a lot of the occasions you received’t want to make use of them.
Say if there’s a robust resonance at a really particular frequency (reminiscent of body resonance), static notch filter may be useful. Nevertheless the dynamic notch filter can normally cowl it and so a static notch filter is normally not wanted. You’ll be able to nevertheless strive including a static notch for the identified body resonance and lowering the dynamic notch depend by one and see which technique works higher in your setup.
Yaw Lowpass Filter
The default yaw lowpass filter at 100Hz cutoff has minimal latency penalty subsequently it may be left untouched. Whoops can particularly profit from Yaw Lowpass filter because it helps to scale back yaw spin in collisions.
PID Tuning
To tune PID utilizing Blackbox, I shall be following the “Basement Tuning” methodology utilizing PIDToolBox. It’s beginner-friendly and you’ll actually do it in your basement/mattress room therefore the title. Principally you simply have to carry out a collection of quick flights with barely completely different PID values, then evaluate the logs to seek out the optimum positive aspects.
Throughout flight, it’s best to transfer the quad round in pitch and roll axis, easy sufficient. You’ll be able to study extra in regards to the basement methodology on this video by PIDToolbox.
Though they name it the “basement tuning methodology”, I’m actually not comfy doing this indoor. I had a few “fly to the moon” incidents prior to now and I virtually drilled a gap within the ceiling, so I at all times attempt to do these checks within the backyard or within the native park.
Fee Profile and Angle Mode
It takes some good line of sight flying abilities to carry out the basement tuning flights. It’s not straightforward to maintain the drone managed in confined area with out hitting the partitions. To make it simpler, do that charge profile (Precise Fee):
- Middle Sensitivity 250
- Max Fee 400
- Expo 0.00
It has low max charge, so it’s much less prone to get uncontrolled for those who transfer the sticks an excessive amount of. The excessive and linear heart stick sensitivity ensures the stick inputs are large enough for the logs.
You’ll be able to even carry out this take a look at in Angle mode which makes it even simpler than charge mode. In line with the writer of PTB, this works simply in addition to in charge mode, however it is advisable do the next first:
- Calibrate accelerometer on the Setup tab
- Set Angle mode power to 100 in PID Profile Settings
- Click on Save
Discovering P/D Stability
To begin with, decrease these positive aspects in order that they don’t intrude with our tuning:
- Set the “Stick Response” slider (Feed Ahead) to 0
- Set the “Dynamic Damping” (D Max) slider to 0
- Set the “Drift-Wobble” (I positive aspects) slider to 0.2, it’s low sufficient that it shouldn’t introduce overshoot but have just a bit I phrases to assist stabilize the quad higher, makes it simpler to regulate
Modify the “Damping” (D positive aspects) slider, begin with a minimal worth you wish to take a look at. For a typical 5-inch FPV drone, 0.6 is an efficient start line.
Here’s what you wish to carry out within the flight:
- Arm and hover
- Consistently shifting the roll and pitch stick for 20-30 seconds, the extra actions the extra correct it will likely be
- Do as huge strikes as you possibly can with out hitting the partitions (ideally full stick deflections)
- You’ll be able to transfer each pitch and roll collectively so long as you possibly can maintain it beneath management
- Attempt to not cease/hover for too lengthy throughout flight, and be as steady as you possibly can
Elevating the Damping slider by 0.2 every time and repeat the flight: e.g, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. Whenever you increase D acquire too excessive, your motors will sound tough, subsequently you possibly can’t at all times take a look at the final one or two values, which is okay.
The quickest approach to change slider worth is by going into Betaflight OSD menu, Profile, Simplified Tuning. However in case you are unable to do that then simply plug within the USB cable and use the Betaflight Configurator.
It’s a good suggestion to alter battery each 2-3 flights to make sure the outcome isn’t affected by voltage. Energy cycle the quad by unplugging the battery earlier than each flight so it creates a brand new log. Or just select “Save and Reboot” within the OSD menu so that you don’t have to unplug.
16MB reminiscence must be sufficient for six 30-second flights for those who time it effectively.
After you could have accomplished all of the flights, obtain them to your pc. To prepare the logs higher, I’ve a folder construction created for this course of, obtain right here: https://drive.google.com/file/d/1tx1AV2lOMgknAwIB3VFhqP1i6VpDLVjr/view?usp=share_link
And I rename the logs to one thing like “01 d06“, “02 d08” and many others (01 means first take a look at flight, d06 means damping slider worth 0.6), and put them within the “02 PD Stability” folder.
Load all of the logs in PTB, undergo each and take away the take-off and touchdown components for every log (to do that, allow “Trim” on the best hand panel).
Click on the “Step Resp Software“, choose all of the recordsdata and click on Run. in case you have offset within the curves (gyro curve shifting away from setpoint in direction of the tip), allow Y Correction.
It’s fairly straight-forward, merely choose the most effective wanting line, that’s your optimum Damping slider worth. The perfect response ought to look one thing just like the inexperienced line within the following graph, little to no overshoot. Having a tiny little bit of overshoot is suitable.
In case your traces don’t look clean however have a number of ups and downs, that’s referred to as oscillation, and it’s an indicator that the sign is simply too noisy or your actions aren’t large enough.
The graphs on the best are additionally extraordinarily useful:
- Peak is highest amplitude of the overshoot (ideally the nearer to 1 the higher)
- Latency is the time it takes to succeed in setpoint (ideally the decrease the higher)
When D acquire is low, you’ll get overshoot and even oscillation. As D acquire will increase, there shall be much less overshoot and Peak will lower, however Latency will go up consequently. When D is simply too excessive (undershoot), the preliminary peak may not even attain the setpoint and this isn’t very best. Discover a response that has minimal overshoot and but has comparatively low Latency.
You’ll be able to zoom in and see it extra clearly (or choose fewer logs, and hit Run once more). We solely want to take a look at Roll and Pitch axis.
In our instance, it’s fairly clear the best worth is orange (3) for each pitch and roll, so that will be 1.0.
It’s fairly widespread to have a unique PD steadiness on pitch and roll as a result of completely different weight distribution. If that’s the case for you, take the Damping slider to the place you need for pitch, write down the pitch D acquire, then take the Damping slider to the place you need for roll, and alter the Pitch Damping slider to match the pitch D acquire you simply wrote down.
Generally it’s higher to be a bit extra conservative and keep away from having D acquire too excessive. In case you are on the fence, at all times go together with much less D acquire (a better P/D ratio), so you possibly can increase your general PID positive aspects greater on the finish since D is normally the limiting issue.
What I’ve discovered is that the step response software tends to be fairly delicate and the P/D steadiness may be decrease than what I’d personally favor. So I usually bump up P/D steadiness by 5-10% after discovering a super worth. That’s simply my private desire, you can provide {that a} strive if you’d like.
Drone dimension additionally impacts PD ratio, bigger drones are likely to have greater P:D ratio. For instance a 5″ would possibly use 0.8-1.1 Damping slider whereas a tiny whoop would possibly use 1.4-1.6.
Discovering Max D Achieve
Do the identical take a look at for Grasp Multiplier slider at 0.2 steps, e.g. for five″ drone, that will be 0.8, 1.0, 1.2, 1.4, 1.6 1.8.
Be very cautious although, don’t stand too near the quad throughout this take a look at, since you would possibly hit a degree the place D is simply too excessive and the quad can shoot up. Pay shut consideration to motor noise, whenever you hear thrilling oscillation it’s best to cease.
You would possibly discover the shapes of the step response don’t change a lot between completely different values, and the Peak values keep roughly the identical too. That’s as a result of the form of the response curve is principally decided by the P/D ratio. By rising the positive aspects received’t have a lot of an impact on the response, however by bumping up P/D positive aspects can scale back Latency.
You could have reached the best Grasp Multiplier acquire when one of many following occurs:
- you hear thrilling oscillation – you possibly can’t enhance D acquire anymore
- or the latency doesn’t lower anymore (or little or no) – meaning it has reached the higher sure tuning window, motors are working on the hardest and you aren’t getting anymore efficiency out of them
How excessive your positive aspects can go is set by how noisy your construct is and the way a lot filtering you’re utilizing. Much less filtering permits for greater PID positive aspects. Generally it’s higher to be a bit extra conservative and switch the Grasp Multiplier slider down a notch or two when you could have discovered the max worth, and to not push D acquire to the sting could be safer within the occasion of a bent prop. Word that drones utilizing greater cell depend battery (greater voltage) have a tendency to permit decrease D positive aspects, e.g. on a 6S quad, D positive aspects may be within the 30’s, whereas on 4S they’re normally within the 40’s.
In my instance, 1.6 appears to be the worth that offers us the least quantity of latency, and there may be not a lot enchancment going as much as 1.8.
You would possibly or may not be capable to hear the thrilling oscillations. To verify, merely go to Spectral Analyser and plot Dterm. Because the positive aspects get greater, the motors will make an exciting sound that peaks round 40-80Hz (particularly as you ramp up throttle). In case you see noise at this frequency vary creeping up with greater positive aspects, then you understand for certain you could have an oscillation beginning that’s PID associated.
On this instance, you possibly can clearly see that peak round 60Hz for 1.4 (olive), 1.6 (inexperienced) and 1.8 (cyan). Though 1.6 exhibits enchancment in latency, I personally wouldn’t threat it. I’d in all probability go for 1.3 and even 1.2 on this instance simply to be protected.
It’s nonetheless controversial whether or not it’s higher to have extra Dterm filtering and better D acquire, or much less Dterm filtering and decrease D acquire. However by no means run much less Dterm filtering and excessive D acquire or disasters can occur whenever you hit a department or have bend a prop! It’s no joke 🙂 Talking from expertise right here:
In case you verify setpoint monitoring now (plot Gyro and Setpoint), it’s best to discover the quad monitoring fairly effectively. The 2 line must be roughly parallel (that means the quad is accelerating and decelerating on the similar charge as Setpoint), however there’s nonetheless fairly a giant hole between them, which is latency! Within the subsequent step, we’ll scale back that hole utilizing Feedforward.
Tuning Feed Ahead
Feed Ahead accelerates your quad whenever you transfer the sticks, making your quad extra responsive and observe setpoint nearer.
P time period is sort of gradual in comparison with Feedforward as a result of it solely begins to react when there’s a PID error. Feedforward measures the speed of stick deflection – how briskly you’re shifting the sticks. It doesn’t rely upon gyro knowledge, it will get the motors shifting as quickly because the the stick strikes, subsequently it’s so much quicker than P time period.
When tuning Feed Ahead I favor to do some snap rolls and flips and verify Gyro/Setpoint traces. Use your standard charge profile, or a default charge profile in Betaflight (simply change to the unused charge profile) to get a good max charge at full stick.
As an alternative of utilizing the step response software in PTB, we are able to simply verify setpoint/gyro traces in BE, the gyro must be monitoring setpoint even higher than earlier than (much less delay). In the most effective circumstances the gyro could also be proper on prime of setpoint. If Feedforward overshoots (gyro strikes earlier than setpoint), then feedforward is simply too excessive. Within the following demonstration, 0.5 is approach too low, 1.0 remains to be not excessive sufficient, however 1.5 is a tiny bit an excessive amount of and overshoots. I believe Feedforward at 1.3-1.4 ought to do it on this instance.
Doesn’t matter what your flying type is, feedforward may be helpful and doesn’t apply solely to sure kinds of flying. Even cinematic flying can profit from a great quantity of feedforward, in case you are shifting your stick easily and slowly, then feedforward received’t kick in anyway. Whenever you want snappy response FF will scale back the latency between stick enter and quad response. If you need clean flying, simply use expo, extra RC smoothing or decrease your charge.
There’s an non-obligatory setting, Feedforward enhance (FF Increase). You wish to enhance it if gyro lagging behind setpoint initially of a transfer, however catching up in a while. However it’s best to scale back it if gyro will get forward of the setpoint initially of a transfer, however falls behind later.
Tuning I Achieve
The perfect I time period is just about a really feel factor to some extent, you don’t want loads of I acquire when you could have optimum P and D positive aspects, simply want a minimal quantity of I acquire to maintain the drone from drifting and wandering. Check out my methodology of tuning I right here. In case you are cruising ahead with minimal stick inputs, the drone ought to maintain its place for a time. If there’s any drifting you then want greater I acquire.
I time period has a REALLY WIDE tuning window particularly for highly effective 5″ quads, 0.5 to 1.5 within the I time period slider would in all probability work tremendous. That’s why we are able to tune the whole lot else and tune I time period final. With a excessive I acquire your quad will really feel extra exact, however once I acquire is simply too excessive your quad could have gradual oscillations and also you wish to keep away from that.
In case you are making an attempt to push I acquire as excessive as potential, you possibly can strive shifting I acquire slider up till you could have gradual bouncebacks and oscillations throughout quick strikes, then come again down a notch or two.
Since we now have added FeedForward, and the Gyro/Setpoint are monitoring so carefully, the Step Response software in PTB received’t be efficient for locating the I time period. So I usually tune I acquire by wanting by means of the goggles and listening to the motors.
Due to the function “I-term loosen up” in Betaflight, you need to use very excessive I acquire with out a lot of the adverse results. What I discovered when setting I time period too excessive is it’ll make the traces look bumpy when doing flips and rolls. So I are likely to set I on the decrease aspect for my freestyle rigs, simply sufficient to maintain the quad from drifting attributable to wind. Utilizing Anti-Gravity can enhance your I acquire temporally throughout throttle pumps to scale back nostril wanders, so I normally don’t discover the necessity to have very excessive I acquire. For five″, I usually depart it slightly below 1.
With I time period loosen up, you possibly can alter the cutoff based mostly on its responsivenes. For freestyle drones, you possibly can usually depart it at default. For racing drones, enhance it to 30. For heavier drones like cinelifters and seven″ lengthy vary carrying GoPro, you possibly can set cutoff to 10.
Dynamic Damping
Dynamic Damping boosts D acquire to the utmost throughout sharp strikes, however doesn’t enhance up throughout regular flight. This reduces motor warmth.
Lowering Damping slider whereas shifting Dynamic Damping slider so D Max maintains the unique D acquire, however your By-product acquire is now decrease which is used throughout regular flights and maintain the motor cooler.
Different Settings
Anti Gravity Positive aspects
As talked about, whenever you punch out and let go of throttle, the drone would wobble and nostril dip. Anti Gravity (AG) can enhance I acquire temporally when throughout throttle pumps to scale back these undesirable dips. Nevertheless whenever you set AG acquire is simply too excessive, your quad could stutter whenever you let go of throttle (fast oscillation), as a result of AG boosts each P and I.
Default is 8, scale back it for those who see wobbles throughout quick throttle modifications. For five″ freestyle drones, I discovered 4 to eight a great vary.
You must tune AG by wanting within the goggles.
Dynamic Idle
Dynamic Idle Worth 30 to 35
Dynamic Idle helps to enhance stability, higher propwash dealing with and decrease likelihood of ESC desync. The draw back is it’s possible you’ll lose grasp time. By rising motor pace when throttle is at zero, it improves management authority of the PID controller and low throttle enter responsiveness. There are additionally different advantages reminiscent of sharper flip and roll stops, extra responsive in low throttle and simpler braking and many others.
When Dynamic Idle is ready, Static Motor Idle (in %) within the Motors tab is disengaged.
To setup Dynamic Idle, it is advisable
- allow bi-directional DShot within the Motor Tab (if you have already got RPM filter enabled, you’re all set)
- set an acceptable Idle RPM worth within the PID Tuning web page (enter 30 to 35 for five″)
The really helpful Idle RPM worth relies upon so much on propeller dimension and pitch, smaller and decrease pitch propellers usually require greater worth. For 7″ you possibly can usually set this to 14-28, for five″ drones, 20-40, and for 3″ it’s greater at 33-66. When it’s windy it’s also possible to set this greater to counter.
| Prop Sizes | Excessive Pitch Props | Low Pitch Props |
| 31mm/1.2″ | 84 | 167 |
| 40mm/1.6″ | 62 | 124 |
| 2″ | 50 | 100 |
| 2.5″ | 40 | 80 |
| 3″ | 33 | 66 |
| 3.5″ | 28 | 57 |
| 4″ | 25 | 50 |
| 5″ | 20 | 40 |
| 6″ | 16 | 33 |
| 7″ | 14 | 28 |
| 8″ | 12 | 25 |
| 10″ | 10 | 20 |
Worth too excessive, you lose grasp time whenever you let the drone fall the other way up (the motors push more durable in direction of the bottom). A excessive worth may also are likely to make the quad “hover” a bit extra even at zero throttle, making throttle administration a bit more durable. When worth is simply too low, you threat low throttle instability.
To set the worth, is dependent upon what ESC idle you had beforehand (default is 5.5%), take a look at your motor within the motor tab, you need to use a smoke stopper or bench energy provide to restrict present in case it goes uncontrolled. Spin the motor on the ESC idle worth, e.g. for five.5%, transfer slider to round 1055, and see what the reported RPM worth is (it is going to solely present this for those who allow bi-directional DShot). Then this RPM worth could be the best worth in your dynamic Idle worth (divide it by 100).
Throttle Increase
Default worth is 5, works for many freestyle builds. It boosts your throttle worth when you find yourself shifting throttle stick up out of the blue to present you additional energy, it provides you an influence enhance but in addition makes throttle extra unpredictable. It doesn’t have any impact whenever you transfer throttle stick slowly although. In case you discover throttle is difficult to handle you possibly can scale back it. I do know some racers even disable throttle enhance totally by setting it to 0. You’ll be able to experiment with smaller values and see what works for you.
Voltage Sag Compensation
It reduces the utmost motor drive worth when battery is full, and will increase it because the battery voltage goes down. It provides extra constant flight efficiency all through the entire flight.
Thrust Linearization
Allow Thrust Linearization, 20%.
It will enhance PID to enhance responsiveness and management authority at low throttle, whereas reducing PID at prime throttle to scale back oscillations (similar impact as TPA). It will probably assist with nostril dip too. That is particularly really helpful for whoops and for those who use 48KHz PWM frequency on ESC. It’s additionally helpful when TPA alone isn’t sufficient to handle excessive throttle oscillation.
Because it boosts PID at low throttle, you would possibly wish to drop the grasp multiplier slider down a notch or two if motors get sizzling.
TPA
Do a throttle sweep once more and verify freq vs throttle heatmap.
In case you are getting oscillations solely above sure throttle stage, TPA may be the answer. It additionally helps to push PID greater with out supplying you with drawback within the excessive throttle vary.
Within the newest Betaflight it solely attenuates D acquire above sure throttle stage (which is normally the reason for the oscillations). Within the older Betaflight it attenuates each P and D, if you’d like you possibly can carry this again by typing in CLI: set tpa_mode = PD.
Usually I favor to set throttle worth in TPA as excessive as potential, so D acquire is extra fixed throughout a wider throttle vary. Be sure to set the throttle worth a bit decrease than the place the place the D time period associated oscillations begin to present up. For instance, if oscillation begins round 1800 throttle, I’d do one thing like this: TPA = 0.75, 1750.
Revisit D time period filtering
In any case these modifications, you possibly can verify D time period filtering once more and see if it is advisable scale back or enhance it.
I Time period Rotation and Absolute Management
There’s no want to make use of these options for FPV Freestyle Drones. These options are largely helpful for line of sight pilots.
Tuning Yaw
I don’t play with Yaw an excessive amount of, default acquire usually works effectively. The tuning window for Yaw is sort of extensive.
Not like pitch and roll that are based mostly on thrust generated by propellers, yaw relies on the inertia generated by propeller rotation. Due to this fact, yaw will inherently be too gradual to overshoot setpoint, and there’s little have to tune yaw PID.
Yaw can be too gradual for D phrases to have any significant impact and it’s usually not required. Nevertheless you possibly can allow it if you’d like, but it surely would possibly introduce extra drawback than it solves, like vibrations and many others. So we’re left with P and I phrases for Yaw.
You’ll be able to tune Yaw utilizing the step-response evaluation like we did with Pitch and Roll. Moreover, if gradual oscillations happen within the again a part of the graph, then I-Time period is simply too excessive. If quick oscillations happen, then P-Time period is simply too excessive.
You probably have yaw shakes when doing throttle pump, you possibly can isolate yaw from the slider tuning, and set Yaw PID individually. To do that, go to the PID tuning tab, within the ‘Slider Mode’ dropdown checklist, choose RP (Roll Pitch), as an alternative of RPY (Roll Pitch Yaw). It will exclude yaw values from the sliders, and means that you can enter PID numbers for yaw. For five″ freestyle and cinematic builds, strive 100 for each P and I’d be a great start line. You too can strive greater values as yaw tends to be fairly gradual reacting.
There is no such thing as a good tune
How good is sweet sufficient? You’ll be able to at all times spend extra time taking part in with filters and PID numbers, and you might even see enhancements however it may be situational and the time you put money into it may not be proportional to the outcome. I usually simply cease when it seems “adequate” and depart it there until I’ve a particular drawback I wish to remedy.
Troubleshooting Suggestions
Unhealthy Gyro
On default Betaflight settings, a 5-inch FPV drone ought to already fly fairly easily. In case your quad has vibration, it may both be mechanical or electrical associated. Generally the Gyro on the FC could cause issues too, although this isn’t widespread.
Right here’s what a foul gyro would possibly appear to be. What tends to occur with a foul gyro, is that one axis is especially noisier than different axes, particularly within the decrease frequency spectrum under 200Hz. In case you rotate the FC by 90-degree, and the noisy axis follows the rotation, then that Gyro might be defective.
On this instance, you possibly can see pitch axis is way noisier than roll and yaw. You too can see bursts of D time period noise within the pitch axis which is attributable to the noisy gyro.
Nevertheless, it doesn’t need to be a foul Gyro, different potential causes are: excessive energy wires close to the gyro, noisy energy to FC, dangerous board design, and many others. You’ll be able to strive utilizing a 1000uF low ESR capacitor on the ESC energy. You probably have already finished that, strive soldering an additional smaller 220uF-470uF cap to the ability of the FC (VBAT/VCC pad).
RC Smoothing
RC smoothing is a must have setting in Betaflight with a view to keep away from concern with feedforward. The suitable RC smoothing settings rely in your specific RC hyperlink, I strongly suggest simply loading the suitable RC_Link preset, it’s one of the best ways to keep away from person errors.
The Auto Issue is maybe one of the crucial vital values, decrease is extra twitchy and responsive whereas a better worth is softer and smoother however extra sluggish. Right here’s a common rule I personally observe:
- 20-25: Racing
- 30: Default worth, nice for Freestyle
- 50: Cinematic
- 90: Extraordinarily clean cruising, delay may be noticeable to some
- 120: The best smoothness potential with out stepping into hassle, however delay is noticeable
Unhealthy gear/pilot require greater RC smoothing too, e.g. Low high quality radio management gear, worn out gimbals, pilots with shaky fingers, and many others. Principally something which may contribute to jerkiness in RC instructions.
If potential, verify black field logs to verify you could have clean setpoints, if the setpoint isn’t clean (has steppings from RC instructions), merely enhance the smoothing barely.
You probably have noise in setpoint that peaks round 50Hz, 150Hz, 250Hz or 500Hz, then there may be in all probability an issue with RC smoothing. These frequencies are widespread packet charges in RC hyperlink. On this instance, it’s Crossfire 150Hz.
In case you are not utilizing sufficient filtering for the RC instructions, you may not have smoothed out the RC sign sufficient and it may create noise on the frequency of your radio hyperlink packet charge.
RC smoothing removes stepping and bumpiness in your set-point, it makes P time period hint much less jerky. Nevertheless it additionally provides delay to feedforward in addition to setpoint, so your quad would possibly really feel a bit bit much less responsive. RC Smoothing is beneficial, however an excessive amount of smoothing defeats the aim of getting quick RC packet charges like ExpressLRS provides.
The objective is to clean out the steppings however not including an excessive amount of delay. If you need smoother RC enter, strive including some extra expo, it has comparable impact but it surely received’t provide the latency penalty.
One of the best ways is to simply load the suitable RC Hyperlink preset as I talked about right here. In case you didn’t load the proper RC_Link preset in your specific RC hyperlink and packet charge, it may additionally trigger issues to Feedforward. On this instance, feedforward jitters as a result of lack of stepping smoothing in RC instructions.
PID Sum too low?
PID_Sum hitting the default 500 restrict right here (50%) as a result of PID are set very excessive on this drone. You’ll be able to increase it to 1000 (in CLI enter set pid_sum_limit=1000) to repair it, but it surely doesn’t at all times make a distinction in flight behaviour as motors would possibly saturate at this charge anyway.
ADC Filter Jitters Inflicting Oscillations
In case you are getting random vibrations and wobbles attributable to feed ahead jitters, regardless that you’ve utilized the proper RC Hyperlink preset or elevated RC smoothing, it might be ADC filter!
Be sure you have turned it off in your radio’s system menu, {hardware} web page.
That is what the feedforward spikes appear to be when ADC filter is tuned on.
Edit Historical past
- Nov 2022 – Information created
- Jun 2024 – Up to date to Betaflight 4.5
