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moteus brushless controller library and tools

Project description

Python bindings for moteus brushless controller

These bindings permit communication and control of moteus brushless controllers.

To use

pip3 install moteus  # or 'moteus-pi3hat' on a pi3hat

The following will report the status of a single controller at the default address of 1 at 1Hz while commanding it to hold the current position.

import asyncio
import math
import moteus

async def main():
    c = moteus.Controller()
    await c.set_stop()  # in case there was a fault

    while True:
        print(await c.set_position(position=math.nan, query=True))
        await asyncio.sleep(0.02)

asyncio.run(main())

Theory

Interactions with a controller are mediated through the moteus.Controller object. When constructed with the constructor argument transport=None (the default) it attempts to find some suitable link on your host system, typically the first fdcanusb or socketcan bus it locates.

Single controller imperative operation can be conducted by using await Controller.set_stop(), await Controller.set_position(), and await Controller.query().

Bus-optimized usage

To optimize bus usage, it is possible to command multiple controllers simultaneously. In this mode, a "transport" must be manually constructed.

import asyncio
import math
import moteus

async def main():
    transport = moteus.Fdcanusb()
    c1 = moteus.Controller(id = 1)
    c2 = moteus.Controller(id = 2)

    while True:
        print(await transport.cycle([
          c1.make_position(position=math.nan, query=True),
          c2.make_position(position=math.nan, query=True),
        ]))

asyncio.run(main())

All of the "set_" methods have a "make_" variant which is suitable to pass to a Transport's cycle method.

This mechanism only improves performance for non-fdcanusb links, such as a pi3hat.

Position mode commands

Controller.set_position and Controller.make_position have arguments which exactly mirror the fields documented in docs/reference.md. Omitting them (or specifying None), results in them being omitted from the resulting register based command.

  • position
  • velocity
  • feedforward_torque
  • kp_scale
  • maximum_torque
  • stop_position
  • watchdog_timeout

Finally, the query argument controls whether information is queried from the controller or not.

Controlling resolution

The resolution of commands, and of returned query data, is controlled by optional constructor arguments to Controller. By default, the commands are all F32, and the query requests a subset of fields as INT16. Here is an example of setting those.

pr = moteus.PositionResolution()
pr.position = moteus.INT16
pr.velocity = moteus.INT16
pr.kp_scale = moteus.F32
pr.kd_scale = moteus.F32

qr = moteus.QueryResolution()
qr.mode = mp.INT8
qr.position = mp.F32
qr.velocity = mp.F32
qr.torque = mp.F32

c = moteus.Controller(position_resolution=pr, query_resolution=qr)

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