I’d like to introduce the qdd100 beta 2!

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This is the newest version of a quasi-direct-drive servo from mjbots. It has a sleek new look, and improved performance all around:

	Beta 1	Beta 2
Peak Torque	12.5 Nm	16 Nm
Backlash	+- 0.2 degrees	+- 0.1 degrees
Voltage Range	10-34V	10-44V
Mass	470g	475g

Comparison from beta 1 to the new beta 2

Additionally, the M3 mounting holes are now 3mm deep instead of the previous 2mm, which gives more flexibility when designing mounts.

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.

Now that I have a bunch of the mk2 servos set and ready to go, a new leg design, a new power distribution board to power them, and a raspberry pi3 hat to communicate with them, I built a new quadruped!  I’m calling this the mjbots quad A1, since basically everything is upgraded.

After I initially assembled the new legs onto the chassis, I realized I had the geometry slightly off and there was some interference through part of the shoulder rotation.  I made up new printed parts and replaced everything in front of the camera.  Thus, watch some high speed robot surgery:

To build a second demonstration quadruped and to generate some development kits, I’ve built up a set of 20 of the mk2 servo.  The production process is working out fairly well, in fact slightly better than I had predicted for overall cycle time.  The servos so far are coming out great, moving smoothly with full power.

I’m planning on building up a set of mk2 servos to test them on a quadruped and make some development kits.  As of now, I’ve got all the materials in house for the build and many things partially assembled!

Because my working environment is otherwise too idyllic and peaceful, I’ve been running the new moteus servo mk2 through its paces.  All day long.  8 hours a day.

This is the same test I ran to verify the controller, only now I’ve done it several times longer to get a better feel for if there are any weak links.  Somewhat surprisingly, the ball doesn’t drop all that often, only once an hour or two.

Earlier I described my design plan for reducing the overall mass of the moteus servo mk2.  Constructing a prototype of this turned out to take many more iterations and time than I had expected!  Along the way I produced and scrapped two front housings, two outer housings and a back housing.

I made one complete prototype which only had the weight reduction applied to some of the parts and lacked a back cover and any provision for a wire cover.  It was the one from the moteus controller r4.1 juggling video:

Update 2020-01-15: All the development kit slots are full.  Thanks for your interest!

I’ve now received all the supplies I need to make up development kits for the moteus controller and to make a test quadruped!

I’m planning on making a few development kits from this production run so others can experiment with the moteus brushless controllers.  Some people have already expressed interest in getting one – you have hopefully been contacted earlier.  If you are interested in getting an opportunity to buy an early access kit and haven’t heard from me yet, fill out this form!

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!