[Feature] Allow gear train to be changed in the middle of a program

[laurensvalk]

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?

Originally posted by @dss0427 in #2507

[laurensvalk]

We could consider adding a method motor.set_gears(gears) for this.

I think we'll want to keep it in the initializer also for backwards compatibility.

[dss0427]

A set_gears() method sounds like a perfect solution.

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On Sat, Dec 20, 2025 at 6:09 AM Laurens Valk ***@***.***> wrote: *laurensvalk* left a comment (pybricks/support#2510) <#2510 (comment)> We could consider adding a method motor.set_gears(gears) for this. I think we'll want to keep it in the initializer also for backwards compatibility. — Reply to this email directly, view it on GitHub <#2510 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AE25HAJMGUSW5IEB6MRHC734CUVABAVCNFSM6AAAAACPTXC2B6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMNZXG4ZTMMZRHA> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[laurensvalk]

When we do this, I suppose we should make the motor stop and coast, whatever it was doing before.

What would you expect the .angle() to be after this? (Anything is possible, just wondering what makes most sense.)

[dlech]

(Anything is possible, just wondering what makes most sense.)

First instinct: For motors without absolute encoders: 0. For motors with absolute encoders: the current absolute value times the gear ratio. (I assume this is already what happens when you start a program?)