Sapog Brake for Fixed-Wing Operation

Alexandre_Borowczyk · May 6, 2020, 2:05pm

Hey,

I have a Kotleta20 and looking to see if there is a propeller braking feature?
I’m want to use it on a e-glider. Hence folding the prop is critical.

Thanks,

pavel-kirienko · May 6, 2020, 7:27pm

Sapog currently does not support this feature, but you can submit a pull request here:

Alexandre_Borowczyk · May 6, 2020, 8:03pm

Would love to give it a try. Have this feature been looked at before.
What would be the starting point?

pavel-kirienko · May 6, 2020, 8:28pm

I recommend adding a new API function or a new parameter to the stop function that instructs the low-level control logic to keep the low-side transistors open:

github.com

PX4/sapog/blob/601f4580b71c3c4da65cc52237e62a163d6a6a16/firmware/src/motor/realtime/api.h#L115


      
          * @param [in] spinup_ramp_duration     Duration of the duty cycle ramp in seconds
          * @param [in] reverse                  Spin direction
          * @param [in] num_prior_attempts       Number of attempts performed before this one, used to switch spinup settings
          */
          void motor_rtctl_start(float initial_duty_cycle, float target_duty_cycle,
                                float spinup_ramp_duration, bool reverse, unsigned num_prior_attempts);
          
          
/**
          * Engage freewheeling.
          */
          void motor_rtctl_stop(void);
          
          
/**
          * Configure PWM duty cycle
          * @param [in] duty_cycle PWM duty cycle [-1; 1], negative - braking, positive - forward
          */
          void motor_rtctl_set_duty_cycle(float duty_cycle);
          
          
/**
          * Returns motor state.
          */

The logic shall ensure that the brake function is activated gradually to avoid excessive power dissipation in case the rotor is not stationary at the time of activation.

Alexandre_Borowczyk · May 7, 2020, 2:41pm

Thanks for the guidance.
I would also have a quick question regarding if the decision between sending the energy back in the battery or sending it to the dissipation circuit while in regenerative braking energy is handle in the code?

pavel-kirienko · May 8, 2020, 5:56am

There is no such circuit available in the hardware. Typically, this case is handled at the DC voltage rail by a dedicated external component or the battery management system controller.