[Feature] Change definition of stalled

[laurensvalk]

Current implementation

Currently stalled is true if:

1. The proportional part of PID exceeds the (configurable) limit and;
2. The motor is stopped, i.e. speed below (configurable) limit and;
3. it has been like this for some (configurable) time.

Suggested improvement: Drop condition 2

Stall detection is mostly used to detect over load in order to stop. We don't need to wait until we are physically stopped to test this.

Doing this makes the stall detection more sensitive, and it makes run_until_stalled work better. We can use a configurable torque limit (test 1 above) instead of a duty limit. This means you can run at any speed and still safely detect soft endpoints. With duty_limit today, this doesn't work because capping it at say 30% means you can't run fast.

I think it is still consistent with our current definition:

Drawbacks
Maybe this is no longer called "stalled" this way, since it may not be fully stopped?

It would also raise the stall flag way sooner when running very fast. This is not technically an issue since all other maneuvers don't look at this flag but it is a bit odd.

Maybe loaded is a better term. Not sure if we need both though.

[dlech]

Instead of changing the definition, can we just add a new run_until_overload(speed, torque_limit, then) -> int and overload() -> bool and deprecate stalled?

I think an overload condition is also useful for discovering that you are trying to run at a speed that the motor is not physically capable of.

[laurensvalk]

Part of this is getting mixed in with pybricks/pybricks-micropython#166 to make some progress.

I need to pull out the motor servo stuff, then rebase that PR.

[laurensvalk]

Yes, as mentioned something like overload could work, I'm just not sure what to do with stalled as having both would be somewhat costly.

I'm wondering if it is acceptable to deprecate stalled by just aliasing it to the new variant. Old scripts would run, but with slightly different behavior.

Although pbio-derivatives will probably want to keep stalled available as well...

[BertLindeman]

Maybe not 100% on this item, but as a simple user I would expect True as the result of motor.stalled() after running motor.run_until_stalled(500).

Currently running this on ('primehub', '3.3.0b8', 'v1.20.0-23-g6c633a8dd on 2023-07-07')

    print("angle before closing", gripper.angle())
    gripper.run_until_stalled(500)
    print("gripper motor stalled ", gripper.stalled())
    print("angle after ", gripper.angle())

which shows:

angle before closing 83
gripper motor stalled  False
angle after  478

[laurensvalk]

By default, run_until_stalled uses Stop.COAST. When it coasts, it is no longer stalled.

If you change it to Stop.HOLD, you should find it still stalled.

[BertLindeman]

It does not.
Not with V3.2.3 and not with v3.3.0b8.
Should I make another discussion to not pollute this one further?