Just wondering, for a small VTOL (5 kg, trimotor, 1000 kV, 12 inch props), would an ESC update frequency of 50 Hz be sufficient?
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There is Q_RC_SPEED for copter-style motors. The default is 490Hz and we never normally change it. I suspect it wouldnt go over the loop rate (400Hz) but you could try setting it to 100Hz or something that your ESCs might like.
SERVO_RATE is for general servos (non-motors) and possibly even plane forward-flight motors, and I have not heard of people changing this from the default.
I ran into a conflict between analog servoes and ESC being on the same output group. An easy fix is just to set Q_RC_SPEED to 50 Hz which then would also be used for servoes. Not sure if 50 Hz is high enough to have a stable control response for the Q plane…
I thought many analog servos have problems when the pulse frequency is above 50Hz. I’m not absolutely positive, but I’d be very surprised if 50 Hz wasn’t enough to control a VTOL servo.
I sure hope someone corrects me if I have this wrong.
Sorry, there was a misunderstanding. I had issues with servoes which were fed 500 Hz update rate, the same one which by default is send to ESC. I have burnt up several ones before pinpointing the problem.
I want to reduce the overall output rate to 50 Hz both for servoes (which are not related to tilt), and ESC, and my doubt is whether a ESC 50 Hz refresh rate is still sufficient to keep the plane stable in hover, i.e. whether a change from 500 Hz to 50 Hz could lead to response lag in motors.
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I would keep ESC rates at 400 Hz (or whatever is the default for VTOL). You can check groups in the .hwdef file for your flight controller.
i think 50hz is way too low for your 5kg VTOL.
You might not need 400 or 490 Hz but around 200-333 is needed to get it tuned fine.
Take a look at the timer groups of your board.
Shouldn’t be too difficult to get 490Hz ESC output AND 50Hz Servo output at the same time.
Thanks for the suggestions. I thought 50 Hz was enough, but I obviously I am not an expert. Will rearrange the setup.
Which type of FlightController do you use?
50Hz will work on very heavy builds which have a higher inertia. Maybe 25kg and above (rough guess).
The lighter the vehicle, the faster the control loop needs to be. Sensor → Filtering → PositionEstimate → Motor output → ThrustChange. There are several components in this loop which greatly affect the overall control loop rate.
If your ESCs support DSHOT its benefitial to use this type of protocol as its a lot faster as PWM 490Hz.
Matek 743 wing.
The ESCs are 80 A Yep stand alone, I use them because of freewheeling option which increases the efficiency in forward flight. They do not have DShot.
This is a good choice but the ESCs are far from perfect for your setup.These YEP ESCs are “normal” RC-Airplane ESCs which are not well suited for hovering vehicles. They are big, heavy and not optimised for fast control loops.
I want to suggest to switch to AM32 ESCs. This is an opensource ESC firmware project specially designed for copters (which includes VTOLs ). Active freewheeling is standard as far as i know.
Sequre 2670 should be a solid choice for your VTOL:
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Thanks for the suggestion. I have maidened the plane some two years ago, and it was hovering satisfactorily then, so the issues I have now are due to some minor changes in setup which resulted in big problems (I switched to ERLS from 433 Mhz DL, by accident burnt up Speedybee FC in the process (a short circuit due to a drop of solder), now there are no Speedybee FC on the market, switched to Matek, Matek required reworking the antivibration base, that lead to resoldering and redoing power lines, also, Matek had a different layout, the change in S1..S12 connectors resulted in analog servoes going up in smoke because of grouping restrictions… A small decision resulted in several days of work and wait times for the FC…
My lemma is: if it is working, do not touch it!
But for a new build I will consider it defintively. The problem with tricopters is that they are not as efficient as they seem on the first glance. That is the reason why mine was sitting there for years. It is very difficult to find a compromise between forward and hover efficiency. For a normal VTOL I would stick with quadcopter layout. In fact, I have built a 9 kg one which hovers on one 30 gram 4 x 1 60 A Speedybee. The Tricopter Yep ESCs weigh 70 grams each! And for forward flight you can use one efficient freewheeling ESC, like YEP.
There is a trick where forward motors are really only used for takeoff and landing and are shutdown during horizontal flight.