How is managed the compliant parameter in the pypot controller?

[Matthieu]

Continuing the discussion from Artist residency: Êtres et Numérique:

@Matthieu

To try to avoid this, I worked on a new primitive I called SmartCompliant which let motors compliant but turn them rigid when approaching the limits. It is working quite well, yet it is a bit complicated to tune correctly to have a really smooth behaviour. Promising but it needs further work to reach a satisfying behaviour. If you want to contribute to the code (still at the prototype stage), here is the associated commit:

https://github.com/poppy-project/poppy-software/commit/500954737bb557ec06f41ca3c7f3d2f0154c327f

I have some trouble with my SmartCompliance primitive behaviour. I wondering if it is not due to the fact that the compliance is not set as fast as I think.

I saw in the controller module the compliance was not added by default as a read/write loop:

self.add_sync_loop(50, self._get_pos_speed_load, 'Thread-get_pos_speed_load')
self.add_sync_loop(50, self._set_pos_speed_load, 'Thread-set_pos_speed_load')

self.add_write_loop(10, 'pid_gain', 'pid')
self.add_write_loop(10, 'compliance_margin')
self.add_write_loop(10, 'compliance_slope')

self.add_read_loop(1, 'angle_limit')
self.add_read_loop(1, 'present_voltage')
self.add_read_loop(1, 'present_temperature')

So:

1. What happens when I set the compliance of a motors at 50 Hz ?
2. Is it possible to add a custom read/write loop when we create a robot ? For example:

poppy = pypot.robot.from_config(...)
poppy.something.add_write_loop(50, 'compliant')

[Pierre]

So, as you can see by directly looking inside the code of the controller, the compliance is actually synced inside the pos/speed/load loop.

def _set_pos_speed_load(self):
    change_torque = {}
    torques = [not m.compliant for m in self._motors]
    for m, t, old_t in zip(self._motors, torques, self._old_torques):
        if t != old_t:
            change_torque[m.id] = t
    self._old_torques = torques
    if change_torque:
        self._dxl_io._set_torque_enable(change_torque)

    rigid_motors = [m for m in self._motors if not m.compliant]
    ids = tuple(m.id for m in rigid_motors)

    if not ids:
        return

    values = ((m._values['goal_position'],
               m._values['moving_speed'],
               m._values['torque_limit']) for m in rigid_motors)
    self._dxl_io.set_goal_position_speed_load(dict(zip(ids, values)))

We implemented the synchronisation of the compliance this way to “bypass” the standard dynamixel motor behavior which re-enables the torque when setting a goal position. This should be explained in the doc (added to my todo list ;)).

To answer your two questions:

1. It will indeed be synced at 50Hz. Yet, I don’t really know what happened if you keep changing the compliance and the goal_position at 50Hz. I don’t have a setup to test this right now, but I’m definitely interested in knowing what would happened. If you test it, let me know!
2. It is possible yes, but as the compliance is already synced it is a bad idea

[Matthieu]

@Pierre

We implemented the synchronisation of the compliance this way to “bypass” the standard dynamixel motor behavior which re-enables the torque when setting a goal position.

It’s true, I had forgotten that point …my bad.

Thanks