SkyCat parachute triggering

Hi all,

I am working on integration of a SkyCat parachute with the dual trigger V4 pro module. This accepts 50Hz PWM at 1-2ms range. At 2ms the parachute is deployed.

Here are some important settings:
SERVO13_MIN: 1000
SERVO13_TRIM: 1500


The servo 3-pin cable from the parachute is connected to my PixHawk Cube Orange rail AUX5, but no signals from the FCU seem to be fed to the trigger unit. I can see this, since the trigger should blink green LED upon 1ms PWM, and blink red LED upon 2ms PWM (chute triggered).

Moreover, if I connect the same cable to an RC receiver output or to a servo tester, the above mentioned expected behavior is occurring. Thus, I believe it has to do with the PWM signal from the Cube. Any help/ideas or parameters I should check will be appreciated at this stage.

With thanks,

params.param (17.5 KB)

By default Ardupilot doesn’t send any PWM to the output unless it is armed. You can set BRD_SAFETY_MASK to an appropriate value to override this behavior for parachute channel.

Should SERVO13_FUNCTION not be 27 for the Parachute?

Interesting! However, after checking BRD_SAFETY_MASK it seems I had already disabled safety switch check for this SERVO.

You stand correct, I tried with 27, but same behavior. I will have to edit the post for clarity.

To help any other user with similar problems, this issue is related to the peak-to-peak Voltage of the PixHawk Cube PWM AUX signals. The internal resistor of the SkyCat parachute on the signal channel is not big enough, which leads to a voltage drop of the PWM pulse to less than 2.5Volts peak-to-peak (~2.2Volts) when sending pulses. If you connect to one of the MAIN ports, which can output 5Volts, the voltage drop is not as significant (~4Volts) and thus the PWM width can be measured by the parachute trigger mechanism. All mentioned measurements where carried out with oscilloscope.