Copter: pins high during boot causes problems for parachute release

[rmackay9]

The parachute release can use a servo or a "relay" (an i/o pin). These are going high when the APM and Pixhawk both boot and could lead to a parachute release on the ground.

[rmackay9]

After some more investigation it looks like this is a tough problem to fix. On the APM2 the pin is only high for a very short period of time and it's possible that we can fix this with some changes within the AP_HAL area (I've looked but haven't found out exactly where yet).

For Pixhawk however the relay pins seem to be pulled high immediately as soon as the board is powered and long before the PX4Firmware or ArduCopter software starts running. This means that it's a very low level setting somewhere that I'm not familiar with. I've ping'd the px4dev team and maybe they will have some ideas.

[rmackay9]

Feedback from the PX4 guys is below and it looks like it'll be very difficult to fix on the Pixhawk. It may still be possible to get it working better on the APM2.

The [Pixhawk[ “Aux” pins are PWM outputs, not relay drivers. They idle high because of the way the line drivers work; this reduces the risk of wild servo glitching when the driver isn’t running.

It’s very unsafe using a voltage level signal for this sort of control, there is really no good way to guarantee the behaviour of outputs from the SoC (and thus the line drivers) during startup / reboot. You will want to use a more positive control method; PWM or CAN would be my recommendations.

[rmackay9]

Tridge has added the ability to set the relay to be low on active. I.e. it starts high but goes low when it should release the parachute. Would this help resolve the issue?

[squilter]

Probably, but it doesn't solve #1235

[rmackay9]

We will not be able to fix this so closing.

[bbasso]

Ok, thanks for looking into this @rmackay9 and @squilter ... Actually i'm totally fine with the relay pulse on boot so long as we can log it, but I bet that's hard to do for the same reason--the pulse happens before the firmware starts running.