Questions after testing Myxa

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I’ve been doing some wind tunnel testing of a propulsion system with a few controllers; and I am very happy about the efficiency gains I am seeing with the Myxa when comparing to others ESCs. During testing, several questions have come up and I’m hoping the forum can help answer:

  1. In current control mode, even with oversaturate turned on, the maximum RPM is less than than other ESCs we are testing. Is there anything else we can do to get a higher rpm (about 5% higher).

  2. Does the myxa’s aluminum enclosure have thermal paste inside which will need to be replaced if we open the case? (We are considering swapping the bullet plugs to a larger size to adapt to our setup)

  3. We require a brake when going to idle throttle; it looks like it will hopefully be in the next firmware release. Is there any update on when we can expect this?

  4. In voltage and RPM control mode, ramping down the throttle quickly will send power back to our power supply and cause it to over-voltage shutdown. Is this expected?, and could this potentially damage other electronics when installed on an aircraft? Why does this not occur in current control mode?

  5. If I am controlling the Mxya over RCPWM, do I have to connect the 5V wire between the flight controller and the mxya’s AUX_VDD port?

  6. What does the ctl.hard_stop parameter do? What does the rcpwm. hysteresis parameter do?

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  1. You can try lowering the PWM frequency a bit. The modulation includes a fixed 1900-ns wide sampling window which is one of the reasons you’re observing a lower maximum speed. At a lower PWM frequency, the window of the same absolute duration will have a lower relative duration, which will increase the maximum modulated voltage.

  2. There is a thermal pad, not a paste. Its behavior upon reassembly is not specified so we are unable to advise here. You can order a replacement from the vendor directly: https://www.arctic.ac/en/Thermal-Pad-APT2560/ACTPD00001A.24

  3. What you described is the default behavior. You can change it by setting ctl.hard_stop but that doesn’t seem to be what you need. Hard stop means that when the device receives a near-zero setpoint, it switches back to idle state immediately. The motor is then stopped on its own, in a non-controlled manner, until the drivetrain runs out of energy. By default this option is disabled, which means that the device will not relinquish motor control until the motor speed is below the minimum.

  4. Of course, it’s expected, that’s how regenerative braking works. You can install a transient voltage suppressor to combat this, use a voltage-triggered braking resistor, or install an additional capacitor bank, depending on the amount of energy reclaimed. In the current control more, regenerative braking does not occur unless you command a negative current setpoint, which is linearly proportional to torque so that as long as the current setpoint is non-negative, the torque is also non-negative, hence no braking occurs.

  5. No.

  6. rcpwm.pulse.hyst sets the zero setpoint deadband (in seconds). If the pulse duration is within this difference from the configured neutral, the signal will be interpreted as zero.