VOXL 2 IO - 8 PWM channels & Futaba (SBUS) Rx
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@Gary-Holmgren , can you help me understand your set up better? Are you already using a ModalAI esc with 4 outputs and want to add another 4? Is the reason for going to dshot due to the fact that ModalAI esc does not support 8 outputs?
By the way, ModalAI esc does have support for changing direction in real time, but i am not sure if PX4 has this ability to command negative rpms (mainly, the mixer would need to do that).
Alex
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@Alex-Kushleyev Yes of course, I am trying to experiment with ground vehicles but in order for proper operation the motors need to reverse direction for forward and reverse driving. I dont have a modalai in my setup. I wanted to have 4 channels of dshot so my motors could allow for forward and reverse operation, and since the other 4 PWM are still available on the M0064, I could use them for other servo/actuators. I am trying to understand how others may have configured the UGV or rover options using voxl2/ESC combos but have had no luck in having a working setup.
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@Alex-Kushleyev Im starting to think the problem may be my 4in1 ESC I have chosen to power the motors as its meant for drone motors not drive motors. Although I dont see why it wouldn't work since turtlemode allows you to reverse motor direction on demand. I guess I dont know what PX4 expects for an ESC of that vehicle type as there is no documentation I could find on what ESC to use.
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Is your ground vehicle a direct drive BLDC (or do you have a gear box?). Direct drive motors usually require FOC control because wheels typically spin much slower than drone propellers and you need frequent start / stop and high torque / low speed operation.
Do you have an ESC that uses FOC control with dshot input?
Non-FOC control would work if you have a gearbox, but there may still be some jittering at very low RPM.
Alex
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@Alex-Kushleyev Yes it does have a gearbox, and good to know I considered using FOC for avoiding it but I needed quite a bit of torque.
This is the ESC im currently using as it supports PWM/dshot/etc but its just a basic 4in1 meant for flight so I am not sure if I can confugure it to otput bidirectionally ex: 1500uS is zero 1050 is full reverse and 1950 is full forward.
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@Gary-Holmgren, do you have any ModalAI ESCs? If so, which one? I can help you test it with a geared BLDC motor.
Alex
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@Alex-Kushleyev Unfortunately I do not have one, but if that is the only solution here I would think about getting one.
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@Gary-Holmgren , since you already have the IO board M0065 and the Tmotor ESC, you can try the M0065 approach. I will follow up in a few days.
Meanwhile please make sure that you can communicate to VOXL IO (M0065) board from your Linux PC or VOXL2 using
voxl-esctools. You should be able to runvoxl-esc-scan.pyand the board will be detected (if using VOXL2, you can plug M0065 into the 4-pin ESC port) J18 : https://docs.modalai.com/voxl2-connectors/#j18-uart-escvoxl-esc tools: https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc (they are also shipped with the SDK, you can find it in /usr/share/modalai/voxl-esc-tools/)
Alex
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I was just thinking that another option for you is to get a standard reversible ESC that is designed for RC race cars - those ESCs support reversing. I am assuming 1500us pwm signal is neutral , 2000us full forward, 1000us full reverse.
You would need 4 of those and should be able to use PX4 standard PWM output.
It is probably best to use ESCs designed for RC cars, so they are tuned for robust start-up, etc. Those ESCs also often come with their own fans for cooling, since you don't have propellers blowing air over the ESC.
For example, you can even buy a motor with integrated ESC : https://www.losi.com/product/tazer-twin-2-in1-3000kv-brushless-motor-45a-esc-combo-2s-ec3/DYNS1450.html . I have not tried it, but i do have a race car with a Tazer ESC, which is reversible and is controlled by a standard Spektrum receiver.
Alex
