108 lines
5.2 KiB
Markdown
108 lines
5.2 KiB
Markdown
# Tuning the TECS
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To tune the TECS, a helpful resource is the official [TECS tuning guide](https://ardupilot.org/plane/docs/tecs-total-energy-control-system-for-speed-height-tuning-guide.html).
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Make sure you have run an autotune beforehand, and continue with the tuning below.
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In tuning, there are three stages:
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- Prepare to measure
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- Take measurements in the field.
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- Set parameters on the bench, based on your measurements.
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### Preparation
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- [ ] Set `LIM_PITCH_MAX=4500` (centidegrees), or something similarly high.
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This is the maximum pitch you'll be achieving in FBWA, and you don't want to be limited by this while trying to tune.
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- [ ] Set `LIM_PITCH_MIN=-4500` (centidegrees) or something similarly low.
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This is the minimum pitch you'll be achieving in FBWA, and you don't want to be limited by this either.
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- [ ] Set `THR_PASS_STAB=1` to avoid mapping your throttle to a curve in some modes. This is important because you want a raw (non-remapped) throttle value when measuring.
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- [ ] Add the airspeed and pitch angle elements to the OSD so you can actually take the measurements.
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- [ ] Enable throttle battery voltage compensation with `FWD_BAT_VOLT_MIN`/`FWD_BAT_VOLT_MAX`. Set the max to `4.2 * num_cells` and the min to `3 * num_cells` for Li-Ion and `3.5 * num_cells` for LiPo batteries. This makes your measurements more accurate, as a partially-depleted battery won't make your motor run slower and skew the results.
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### In the field
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You should perform the measurements in four stages, all in the FBWA mode:
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#### Fly straight
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Fly straight and note down:
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- [ ] The maximum speed you want to be flying at (in km/h).
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- [ ] The throttle percentage at that maximum speed. Use the stick position, not the OSD item.
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- [ ] Start a turn at the maximum bank angle (full roll deflection to one side) and note the slowest speed you can fly at without stalling.
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- [ ] Fly straight at a speed at least 15% higher than the stall speed from the previous step, and note that speed. This is your trim speed.
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- [ ] Note the throttle percentage at that speed. Use the stick position, not the OSD item.
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- [ ] Turn throttle to 0 and pitch down a bit so you don't stall.
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Note the minimum amount of down-pitch required to keep you from stalling (this should only be in the 1-3 degree ballpark).
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#### Fly up
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Set the throttle stick to the maximum throttle percentage from the previous step and start slowly pitching up until your airspeed equals your trim speed from the previous step.
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If you're higher than that speed and need to climb more, change `LIM_PITCH_MAX` to something higher and try again.
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Note down:
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- [ ] The pitch angle (in degrees).
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- [ ] The vertical speed from the variometer (in m/s).
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#### Fly down
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Set the throttle to 0 and start pitching down until your airspeed equals your trim speed from the previous step.
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Note down:
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- [ ] The vertical speed from the variometer (in m/s).
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#### Fly down more
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Keep the throttle at 0 and pitch down until you reach your desired max descent rate in auto modes, keeping in mind not to exceed your desired maximum speed from step 1.
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If you're lower than that speed and need to pitch down more, change `LIM_PITCH_MIN` to something lower and try again.
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Note down:
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- [ ] The pitch angle (in degrees).
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- [ ] The vertical speed from the variometer (in m/s).
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You're done with this step.
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### On the bench
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After you have the above measurements, you're ready to tune things. You can use the automatic calculator:
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### [TECS tuning calculator](/ardupilot/tecs-tuning-calculator.html)
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Otherwise, you can do things manually, following the steps below, but you should really use the calculator instead.
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For the level flight measurements:
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- [ ] Set `ARSPD_FBW_MAX` (m/s) to something a bit less than the maximum airspeed you achieved in level flight.
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- [ ] Set `THR_MAX` (percentage) to the throttle percentage at max speed.
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- [ ] Set `ARSPD_FBW_MIN` (m/s) to the slowest speed you could turn at without stalling (maybe go a bit higher for some margin).
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- [ ] Set `TRIM_ARSPD_CM` (cm/s) to your trim speed.
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- [ ] Set `TRIM_THROTTLE` (percentage) to your trim throttle percentage.
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- [ ] Set `STAB_PITCH_DOWN` (degrees) to the pitch angle that keeps you from stalling.
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For the ascent measurements:
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- [ ] Set `TECS_PITCH_MAX` (degrees) to the pitch angle you measured.
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- [ ] Set `TECS_CLMB_MAX` and `FBWB_CLIMB_RATE` (both in m/s) to the climb rate you measured.
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For the descent measurements:
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- [ ] Set `TECS_SINK_MIN` (m/s) to the descent rate you measured.
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For the max descent measurements:
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- [ ] Set `TECS_PITCH_MIN` (degrees) to the pitch angle you measured.
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- [ ] Set `TECS_SINK_MAX` (m/s) to the descent rate you measured.
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That's it!
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## Advanced information
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This is some more advanced information on tuning the TECS:
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- If you have a pitot tube and want more altitude precision and more responsive control, you should lower the `TECS_SPDWEIGHT` parameter value below 1.
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- A right `KFF_THR2PTCH` value is crucial for the TECS to work correctly without pitot.
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- The `THR_SLEWRATE` value should be set so that the plane doesn't lose airspeed when you yank the pitch stick to `TECS_CLMB_MAX` degrees.
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* * *
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<p style="font-size:80%; font-style: italic">
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Last updated on March 23, 2022. For any questions/feedback,
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email me at <a href="mailto:hi@stavros.io">hi@stavros.io</a>.
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</p>
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