After receiving many requests via youtube, discord, and email, I’ve finally gone ahead, bitten the bullet, and updated all of the moteus tools to be pure python and work in a cross platform manner. Now, the only thing you need to do to install pre-compiled versions of tview and moteus tool on most* platforms is:

pip3 install moteus_gui
python3 -m moteus_gui.tview    # (or maybe just tview)
python3 -m moteus.moteus_tool  # (or maybe just moteus_tool)

I’ve personally tested these on Linux, Windows, and Raspberry Pi, and others have at least verified basic operation on Macs. Python 3.7 or greater is required.

NOTE 2025-10-29: An updated version of this post can now be found in the official moteus documentation:

• https://mjbots.github.io/moteus/integration/python/

I’m excited to announce new python bindings for communicating with moteus controllers! A simple example from the README:

import asyncio
import math
import moteus

async def main():
  c = moteus.Controller()
  print(await c.set_position(position=math.nan, query=True))
  await asyncio.sleep(1.0)

asyncio.run(main())

This code will try to locate an fdcanusb on your host and use it to communicate with controller with ID 1. All of those details can be customized through code depending upon how you construct things. The library is pure python, although it doesn’t work on Windows currently because it relies on an asyncio aware pyserial wrapper that doesn’t work there.

To date, all of the development tools for the moteus brushless controller have been available exclusively for Linux based operating systems. I’ve been doing some behind the scenes work, and have gotten to the point where moteus_tool now runs natively on windows and can communicate with moteus controllers using a fdcanusb.

Check out the Windows installer for the latest release:

• moteus_host_tools_0.1.2020.1106.msi

To make this work, I started from the excellent grailbio/bazel-toolchain, which provides LLVM toolchains for Linux based systems based on the official LLVM pre-compiled binaries. I forked that into mjbots/bazel-toolchain and added Windows support. It isn’t perfect, because the LLVM project only distributes Windows binaries in installer form, and it isn’t possible to extract binaries from them without specialized tooling. So, this version relies on a manually re-packed compressed archive of all the executables.

The moteus controller has always supported multiple turns when counting positions. It has a one-revolution magnetic encoder built in, but after turn on, it keeps track of how many turns have occurred. However, if you’ve followed previous moteus tutorials, you have probably noticed a persistent caveat that for accurate control, the position of the output shaft needs to stay within a hundred revolutions of 0.0 or so. Now, I’ll describe why that was, and what I’ve done to remove the limitation, allowing unlimited rotations!

At the request of @nichols in discord, I’ve recently implemented a new control mode in the moteus controller, “stay within”. In this mode, as long as the controller is inside the currently commanded bounds, only a feedforward torque is commanded. When either of the optional lower or upper bound is violated, the normal PID controller is used to force the position back to the bound.

Here’s a quick video demo:

Note that this could have been roughly accomplished in a couple of ways by a higher level controller – either by monitoring the position and commanding zero kp/kd scales when inside the boundary, or just solely commanding feedforward torques based on position sensing. However, this approach lets the control run at the full 40kHz of the moteus controller, which results in much smoother operation at the boundary condition.

When I first posted the moteus controller up for sale, the specifications I listed were based on the design characteristics and the testing I had conducted up until that point. Specifically, the peak phase current was just the maximum that I had verified was safe to operate with.

In the interim, I’ve done a fair amount more testing and have concluded that the controller can safely drive higher phase currents than initially posted. For now, I’m increasing the peak phase current to 100A both on the specification sheet and in the default firmware configuration of all newly shipped boards. If you already have a moteus controller and want to take advantage of the higher phase current, chat us up on the mjbots discord and we’ll show you how.

When I first posted the qdd100 beta on mjbots.com, I performed a simple “continuous torque” test where I measured the torque that could be applied indefinitely without thermal limiting in a lab environment. It has come to my attention that other servos rate their “continuous torque” for a much lower value of “continuous”, sometimes only 30s. To make the situation clearer, I measured the time to thermal limiting at a range of torques and updated the product page.

When I was trying my first pronking, I kept having over-voltage issues when the servos were trying to dump power back onto the DC bus, no matter how high I set the voltage limit.  During that test, I was running with a nearly full battery, so my working theory is that the battery protection circuit was disconnecting the battery either because of too high a charging current, or too high a system voltage.  When the battery was disconnected, and the servos were still putting power onto the bus, that resulted in the voltage spiking arbitrarily high, followed by a total loss of power when they all faulted and then nothing was powering the bus at all.