Define a new gear train

[dss0427]

Hi, we want to change an attachment on our spike prime FLL robot and specify the gear train for the new attachment. How do we do that. I tried to stop() and then close() the motor which is what I saw online, but it doesn't like it, specifically the stop(). So, I tried to just close() the motor, but when I re-create the motor, I get an exception "This can only be called before multitasking starts." But we are in the middle of the program, so run_task() has already been called.

Is there a way to change the gear train in the middle of a program?

Thanks.

[dss0427]

It makes sense that I would need to stop and close the motor and then create a new motor object with the new gear train. But, I couldn't get this to work. Any ideas on how to do this?

[jaguilar]

As of now it appears that you cannot make a Motor at all after multitasking starts. See here. I'm not quite sure why that restriction is in place, and perhaps it could be removed. But for now, the idea of redefining the gear train while the program is running seems to be a non-starter.

I think with the firmware as it is your only option would be to handle the gear ratios yourself (e.g. if it's a 2:1 gear ratio, then double whatever controls you send to the motor and halve whatever signals you get back from the motor). You could probably wrap the motor class to handle this if you're finding yourself doing it in a lot of places.

Of course it would also make sense to file a github issue to see if the situation can be improved.

[laurensvalk]

This is because class initialization is not awaitable but it may still take some time, causing it to block multitasking code. We raise an error to be explicit.

For the motor specifically, it usually doesn't take any time, so we could perhaps be more lenient and allow it. But re-initializing a class in the middle of an async run loop feels like a bit of a hack...

But there is a right way to do it. I'll open a feature request for future consideration 😄