One of my goals with mjbots is to make building dynamic robots more accessible to researchers and enthusiasts everywhere. To make that more of a reality, I’m lowering the prices in a big way on the foundational components of brushless robotic systems, the moteus controller and qdd100 servo.

	Old	New
moteus r4.3 controller	$119	$79
moteus r4.3 devkit	$199	$159
qdd100 beta	$549	$429
qdd100 beta devkit	$599	$469

Don’t worry, if you purchased any of these in the last month, you should be getting a coupon in your email equivalent to the difference.

I’ve now got the last custom board from the quad A1 up in the mjbots store for sale, the mjbots pi3 hat for $129.

This board breaks out 4x 5Mbps CAN-FD ports, 1 low speed CAN port, a 1kHz IMU and a port for a nrf24l01. Despite its name, it works just fine with the Rasbperry Pi 4 in addition to the 3b+ I have tested with mostly to date. I also have a new user-space library for interfacing with it that I will document in some upcoming posts. That library makes it pretty easy to use in a variety of applications.

Now that the mjbots.com store has qdd100 quasi direct drive servos, moteus controllers, and the new power dist board, it is time to start getting some useful accessories in stock. While each of these components comes with mating connectors, sometimes you need more or find that a cable harness you built previously needs to be scrapped. Availability of Amass connectors isn’t that great outside of the Chinese market, so I’ve now got XT30U male and female solder cup connectors up in packs of 10. Each pack is just $6.

I’ve displayed versions of this numerous times in the past (May 2019, Feb 2020, March 2020), but now I’m proud to announce that I have a productized version of the power dist and precharge board available in the mjbots store for $79.

This board has convenient connectorization for powering sub-components of your robot, and also provides a smooth pre-charge sequence so that you can safely connect a large battery to high capacitance loads. I made a short video to show it off.

https://shop.mjbots.com is now https://mjbots.com (don’t worry, the old site redirects)! The functionality is largely the same, you can still get your qdd100 actuators or moteus controllers. The biggest differences are 1) it looks slightly nicer, and 2) shipping rates are improved, and international shipping rates drastically so. For instance, DHL “Express” 2 day shipping to some points in Europe is now under $35 USD, whereas previously 2 day shipping was over $300. That is often cheaper than even USPS International Priority – which is typically 2-4 weeks.

I’ve had the qdd100 beta kits available for some time up at mjbots.com, I’m excited to announce that I’ve completed a production run of the beta qdd100’s and they are now available standalone as well.

• mjbots.com: qdd100 beta servo

I look forward to seeing what everyone creates!

Developing the moteus brushless servo controller has been a very long journey, and while it isn’t over yet I have a reached a significant milestone.  The first batch of production moteus controllers are now available for general purchase at mjbots.com and shipment worldwide for $119 USD each!

I’ll repeat some of the specifications here:

• 3 phase brushless FOC control
• 170 MHz 32bit STM32G4 microprocessor
• Voltage: 12-34V
• Peak phase current: 60A
• Dimensions: 46x53mm - CAD drawing in github
• Mass: 14.2g
• Communications: 5Mbps CAN-FD
• Control rate: 40kHz
• Open source firmware: https://github.com/mjbots/moteus

Simultaneously, I’ve got development kits available that give you everything you need to start developing software for the moteus controller out of the box: moteus r4.3 developer kit

First, a limited number of qdd100 servos are available for sale to beta testers!  Check them out at mjbots.com.

After building up the first set of qdd100 servos, I wanted to empirically measure their performance parameters.  Some astute commenters uncovered in my terrible juggling video, that I didn’t actually have any ground truth measure of torque with these actuators.  Given that the ultimate torque is a pretty useful performance metric, it’s a good thing to have a solid understanding of.

I’ve received my first production run of the fdcanusb CAN-FD USB adapters and they are up for sale at mjbots.com!

While this is necessary for interacting with the moteus controller, it is also a fine general purpose CAN-FD adapter.  At the moment, the USB interface is a platform independent line based serial one (Windows, Linux, MacOS).  It doesn’t yet interoperate with SocketCAN on linux, but hopefully that will be resolved in the not too distant future.

While gearing up to make some dev-kits followed by a pre-production run of the moteus servo mk2, I recently received a bunch of frameless rotors and stators.

As with the other custom items, I’ve got some spares of these for sale at shop.mjbots.com if you’re building along with me!  [UPDATE no longer!]

Now it’s time to start building some servos!