We’ve got a new firmware release for the moteus controllers up on github now, 2024-10-29! This update has a few new capabilities, a brief summary is below, while more detailed posts will come in the not too distant future:

MA600 Support: The MA600 from Monolithic Power Systems is an absolute magnetic encoder that uses a TMR (precision tunnel magnetoresistance) sensor. It is much more accurate with less noise than the AS5047P that moteus uses (or the MA732).

I don’t normally post about moteus firmware releases, but there have been many in the last few months that fix some long standing bugs and regressions. First, the current release as of this post is:

• github: 2023-06-22

With that out of the way, here some of the fixes:

Position drift with non-unity gear reduction

It is embarrassing how long this issue has been outstanding, but ever since the flexible I/O system was introduced, there has been an issue where if the gear reduction was configured to a value other than 1, then the output position would drift from the source encoder over time. If control was not active, you would see the position drift, and if control was active, then moteus would report the correct position, but the actual position would drift.

Partly to celebrate moteus controllers being back in stock and partly because a lot of important work has backed up, we’ve just released a new firmware version for moteus (2023-02-01) that has a little bit of something for everyone. Future posts will examine some of these features in more detail, but for now you just get the bullet list:

• Support sending and receiving arbitrary data from a UART configured on either of the auxiliary ports

It has been on github for a few days now, but I’m excited to announce the newest moteus firmware release, 2022-07-11. This release includes some big features, and some quality of life improvements all around.

• Flexible I/O subsystem: This release includes the new flexible I/O subsystem. This adds support for many new encoder types and lets you connect them up in a wide variety of ways.
• Cogging torque compensation: Preliminary support for cogging torque compensation is present in this release. It works pretty well on a number of motor types already, future articles will describe it in more detail.
• Encoder eccentricity compensation: This feature lets you linearize the output position and velocity in the face of non-linear encoder readings. A write-up for it is also forthcoming in the not-too-distant-future.
• Transparent no-BRS CAN-FD communication: If your CAN-FD network is only capable of operating at 1Mbps, and you send queries frames with BRS turned off, moteus will now respond in kind. This eliminates most needs to change the CAN bus frequency due to marginal electrical properties.

This is an exciting time for moteus, and the new features will keep coming!

There’s an updated release out for the mjbots pi3hat which features a useful bug fix and a minor feature.

First, the configuration of automatic retransmission was broken in several ways. The symptoms for previous versions would be that any attempt to change the CAN configuration for a bus would result in all channels attached to that controller having auto-retransmit turned off. Since it was by default on, that would typically result in a decrease in transmission reliability, and in some particular cases with arbitration conflicts, could result in frequent packet loss. Fixing this requires updating both the firmware on the device and the C++ and python libraries. Fortunately, this would only come up if you were communicating with non-moteus devices using the pi3hat, which likely isn’t that common.

This new release makes minor improvements to support for r4.8 moteus boards, notably it makes the Kv and winding resistance calculation more closely match that measured by r4.5 and decreases audible noise when controlling to 0 current or torque.

Get it from github: moteus 2021-09-19

Note, this does require a new version of moteus_tool to be able to flash over CAN, version 0.3.29. You can get it from pypi using any of the normal pip3 methods: https://pypi.org/project/moteus/

Sometimes you find bugs, and sometimes the bugs find you! While getting ready to release some updated qdd100 beta servos, I was investigating speed control in the moteus firmware and discovered an unwelcome surprise!

Voltage feedforward

To improve dynamic response under high accelerations, moteus uses a voltage feedforward term as part of its control loop. When trying to command a specific current, it normally applies a PI controller to determine the resulting D and Q phase voltages to apply. The feedforward component of this looks at the phase resistance and the current rotor velocity, and determines a zeroth order estimate of what voltage would be required to achieve that current under a no-load condition, only using the PI controller to determine the difference.

I’ve posted a new release of the firmware for the moteus brushless controller to github!

• https://github.com/mjbots/moteus/releases/tag/0.1-20200822-1

This release has a number of minor improvements in the host tools (for which there continue to be no distributed binaries, you get to build from source). The biggest improvement in the firmware is the improved low-torque operation as documented here and here. If you have any questions or want help upgrading, hop into discord at #moteus and ask!