Probably one of the most frequently asked questions in the mjbots Discord is “how fast can I send new commands to moteus”, or “how fast can I read the status from moteus”. That may be because you want to perform torque based control in your application and require high bandwidth, or just because you have a high torque to inertia ratio system that reacts on very short time-scales. No matter the reason, the principles that control the maximum rate you can send updates are the same.

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:

	moteus-c1	moteus-r4	moteus-n1
Input Voltage	10-51V	10-44V	10-54V
Peak Phase Current	20A	100A	100A
Continuous Phase Current	5A / 14A	11A / 22A	9A / 18A
Dimensions	38mm x 38mm	46mm x 53mm	46mm x 46 mm
I/O	AUX1 D and E are present as through hole pads. AUX2 is identical to moteus-n1	AUX1: SPI, Hall, ADC AUX2: I2C and UART 3.3V only	AUX1 and AUX2 support SPI, UART, Quadrature, Hall, and I2C. 5.5V and 3.3V provided on each connector. I2C pullups are configurable on each connector.
RS422	None	None	Built-in transceiver for RS422 based encoders
CAN fault tolerance	58V	12V	58V
Price	$69	$79	$149

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!

It continues to be the spring of new products at mjbots (see the mjcanfd-usb-1x from earlier), and today I have some basics that are newly added to the store to make building machines just a bit simpler.

First are two tiny boards to make daisy chaining power and CAN-FD connections easier for boards that don’t have built-in daisy chain connectors like the moteus-n1. First is a junction board for PH3 cables:

And the second is a similar junction board for XT30 cables:

While it may not be technically spring outside, it is spring for product announcements here at mjbots, and I’m excited to announce the next evolution of CAN-FD adapter hardware we’re offering, the mjcanfd-usb-1x:

The major changes from the fdcanusb:

• USB-C instead of USB micro

• Smaller form factor - 30x18mm

• PH3 CAN-FD connector instead of DB9

• Less expensive, only $39

This makes the mjcanfd-usb-1x better suited for in-application deployments and just all around better as a development tool. It can be mounted down more easily, uses the same connector and pinout as moteus, and is compatible with our existing PH3 cables.

The moteus line of brushless motor controllers currently require a CAN-FD host to send commands in order to actually execute a motion profile. moteus has long provided a python library that can be used on desktop operating systems to send commands and parse responses, and recently added a C++ one as well. Next up, and described in this post, is a library for Arduino which provides the ability to command and monitor brushless motors using moteus motor controllers.

Recently I covered a new feature for the moteus brushless controller that improved robustness for velocity control when external torques exceed the maximum allowable control torque. In this post, I’ll cover a feature that can be used for a similar situation in position control, “recapturing position and velocity”.

In some applications, while in position mode, it can make sense to limit the maximum torque during specific periods so that external torques are able to overpower the controller. The most obvious case would be if the maximum torque is set to 0, or the kp and kd scale are set to 0 temporarily. A problem then arises when resuming control, as the “control position” will be wherever it last was, despite the fact that the actual motor have have been dragged by the external torque some distance away. When the torque limit is released, a large transient can develop as the controller tries to instantaneously get back to the old control position.

I’m excited to announce a big price drop for the moteus-r4.11 controller for both single units and in volume!

Quantity	Old	New
1-10	$104	$79
10-99	$99	$75
100-499	$94	$71

We’ve been scaling up production, which enables these reductions of about 25% across the board. moteus-r4 is now by far the most cost effective motor driver with integrated encoder in its class. Here’s a quick comparison with similar products:

	ODRIVE S1	Tinymover R5.2	moteus-r4.11
Voltage	12-50.5V	12-38V	10-44V
Continuous phase current	40A	Not specified	22A
Peak current	80A	40A	100A
Dimensions	66mm x 50mm	40mm x 36mm	53mm x 46mm
Open source	Proprietary FW and HW	GPL FW, Proprietary HW	Apache 2.0 FW and HW
Price	$149	$108	$79

I personally am looking forward to all the new projects that these lower prices enable! Check it out below or join the mjbots Discord to chat and get some ideas for how you can use a moteus-r4.

The moteus brushless motor controller supports several concepts of operation from within its primary “position” mode, including a velocity mode. As documented in the reference, you can run in that scenario using commands equivalent to the diagnostic mode command:

d pos nan V nan

Where V is the desired velocity. However, as with most control operations, there are a number of edge cases that can be useful to handle. When operating purely in velocity mode, the normal PID constants can be interpreted slightly differently:

moteus has long had both automatically tuned current control bandwidth and a built-in low-pass filter for encoder readings. During calibration, these are usually set with moteus_tool’s --cal-bw-hz option, which specifies the current loop (interchangeably called the torque loop) bandwidth. TLDR is that these heuristics have changed as of pypi 0.3.64, hopefully with only improved behavior. Read on if you want to understand more or if you need to resolve problems with something that changed for the worse.