Exciting news! All the existing moteus controllers in the world now have an upgraded default maximum power and upgraded rated maximum power as of release 2025-03-27! Depending upon the input voltage and PWM rate, sometimes nearly twice the amount. First, check out the comparison table, then the rationale:

Background, why a power limit?

moteus brushless motor controllers drive 3 phase PMSM motors, accepting a DC input voltage, and outputting current to each of the 3 phases of the motor. It does so using MOSFET based switching, which alternately connects each phase to either ground, or the DC positive input. As that switching progresses, charge is either drawn, or replenished into, the onboard bulk capacitors.

In the previous post, I outlined a possible path to low cost off-axis encoders to be used with the moteus line of brushless controllers. The first step I took was to try and build a minimally sized breakout board that could be used with the MA732/MA702/MA600 line of hall effect angle sensors. You can get these off the shelf, for instance from tinymovr, but I wanted to see if I could make something a bit more compact, and that had the chip close to a board edge so that it could be used for off axis applications.

The moteus line of brushless controllers all have an integrated “on-axis” magnetic encoder. These encoders are designed to allow moteus to sense the position of a motor’s shaft directly, assuming that an appropriate diametrically magnetized sense magnet is attached to the rotating shaft and the moteus is mounted so that its sensor is positioned over the magnet.

This works great for many applications, but what about hollow shaft motors? moteus supports a few encoder types that will work for off axis encoders, most notably is the AksIM-2. This is a high performance off-axis encoder that gives great performance and is manufactured in configurations for a variety of hollow shaft diameters. However, it does have downsides. First, it comes with a commensurate price tag. In single quantities, the AksIM-2 and magnetic code disc are more expensive than an entire moteus brushless motor controller. Second, only the moteus-n1 has the necessary RS422 transceiver integrated into it. All other moteus boards need an external RS422 transceiver.

A permanent magnet motor controller like moteus has to, at the end of the day, apply voltages to the phase wires of a motor in order to induce currents. Those currents generate magnetic fields that push against permanent magnets in the rotor to make the motor move. I’ve looked at parts of this process before, see “Compensating for FET turn-on time”, but in this post we’ll look at an additional technique that can extend the effective modulation depth, thus increasing the maximum speed that a motor can be driven.

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).

TLDR: As of firmware release 2024-05-20 moteus can now report a pretty good estimate of the electrical (and thus mechanical) output power going to the motor. You can get that through all the language binding options or in tview!

Background

Brushless motor controllers like moteus act like step down DC/DC converters. Their input is a higher voltage and low current, while the output to the motor is low voltage and higher current. If working properly, the output current is driven so as to produce torque at the output shaft.

I made a thing!

With that video out of the way, here is a bit more of a write-up!

Motivation

The hoverbot is a simple 2 wheel balancing robot. I built it to demonstrate how the moteus-c1 can be used to drive hoverboard motors and to demonstrate the capabilities of the pi3hat for high rate control and effective attitude reference calculation. It is powered by a single Bosch 18V cordless drill battery and controlled through an identical websocket based interface as the quad A1, primarily operated by a phone with a paired bluetooth joystick.

I’m excited to announce the newest addition to the moteus line of BLDC controllers, the moteus-c1! The moteus-c1 is a smaller, lower power, lower cost version of the moteus-r4 and moteus-n1, but still packs a big punch.

The top of the line performance metrics for the entire moteus lineup now look like:

The upshot is that for low current motors where RS422 is not required, it is nearly as capable as the moteus-n1 for less than half the price!