Ignore stray gamepad commands

[Achllle]

When I turn on the rover and wait until it fully launches, then turn on the my RC (Spektrum DCs) with the enable button switched to ON, it will send the rover crashing into the wall at full power. Likely the first few commands it sends are misinterpreted or garbled.

This can simply be avoided by making sure the enable switch is turned off when turning on the gamepad or making sure the gamepad is always on before launching the rover.

A hack solution would be to ignore the first few commands received in software.

[ericjunkins]

We've had similar issues at work, where we're using a controller that doesn't have functional safe hardware (as per the ISO standards). We're still able to achieve a functional safe implementation, which could also be used on this project. I'll put all the requirements of what we do, not necessarily all have to be implemented.

no commands can be sent to the drive system until

• X number of packets have been received
• the system trusts the controller inputs
• the Deadman switch has been not active for Y number of packets

The trust is established by the axes (joysticks and any triggers) having a stable settled value that is within an acceptable band around the nominal value (0 for joysticks for instance). It needs to have a certain number of packets with very little variance, within that band In order to say the controller is okay. This helped us get rid of issues that are brought on by resistive-based joysticks instead of more expensive hall sensor ones, things like controller drift. It also made it so if a user was holding any input unexpectedly the robot wouldn't move.

Anyway I'm sure implementing all that is overkill from what's needed here, but that's one solution.

[Achllle]

That's super helpful, thanks for sharing! I hadn't thought about validating package contents before rejecting them. I think indeed we need to land on a solution that is robust since this is a safety hazard but also requires minimal or no configuration. I think it might be time to clone the joystick code and modify it to inject such features.