I’ve got the 6x reduction planetary gearsets back in stock at mjbots.com, now combined into a single product listing for only a little more than the old ring gear – $25 for the whole set! Compare that to the $41 you needed for an entire gearset before!

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!

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:

After having produced the first functional demonstration of the moteus servo mk2, my next step was to decrease the weight.  While I was at it, I made two other changes:

• Axial connections: I switched to a design with entirely axial connectors, which removes the need for 4th axis machining when producing the parts.
• Planet Input Bearing: I switched the planet input bearing to be inserted from the rotor side.  This way, the bearing is captured between the planet input and the rotor, rather than between the planet input and the gears.  That also improves the ability to assemble and disassemble the unit.

Now that I have at least one functioning version of each of the pieces made for the moteus servo mk2 (planet input, outer housing, front housing, and back housing), I integrated all of them together into a functional prototype.

As described in my roadmap, making a new revision of the moteus servo is up there on my list of things to do.  The initial servos were a work of art, yes, but also pretty fragile, very labor intensive, and still not all that robust.  My goals this time around are:

• Manufacturability: The servo mk1 took about 2 or 3 man-days of manufacturing time per servo once all the steps were factored in.  I’d like to get that down to an hour or two at most per servo.
• Robustness: The planet input, outer housing, back housing, and controller cover of the mk1 servo were 3d printed, mostly to save cost and time.  This necessitated adding reinforcing rings on the outer housing, as it is nearly impossible to 3d print something with the required material properties in a single print.  At this point, all of these components should just be made of aluminum like the others.
• Repairability: Once the mk1 was assembled, there was no way to disassemble it, as installing the stator interfered with the ability to remove the outer housing, and the outer housing in place interfered with the ability to remove the stator.
• Convenience: The mk1 servo used the r3.1 moteus controller, which had RS485 connectors sticking straight out the back, and bare power wires coming out the back.  That orientation for connecting things was not terribly convenient in the full rotation leg design, and required making extension cables.  The newer moteus controller has the connectors sticking out the bottom, so the servo needs to accommodate that.

CAD explosion

In my quest to create a more dynamic quadruped, I’ve started accumulating a lot of parts from bulk buys that could be reasonably useful to other hobbyists and experimenters.  To maybe make life easier for everyone, I’ve started up what may be the worlds ugliest online shop where you can buy some of these components.  For now, I have some bearings and custom gears that are useful when building servos for dynamic robots.

My last video gave an overview of what I’ve accomplished over the past year.  Now, let me talk about what I’m planning to work on going forward:

I intend to divide my efforts into two parallel tracks.  The first is to demonstrate increased capabilities and continue learning with the existing quad A0, and second is to design and manufacture the next revision of all its major components.

New capabilities and learning

The first, and most important capability I want to develop is an improved gait and locomotion system.  While the moteus servos in the quad A0 are capable of high rate compliant control, the gait engine that I’m using now is still basically the same one that I made for the HerkuleX servos 5 years ago.  It just commands open loop positions to each of the servos and uses no feedback from the platform at all.  This severely limits what the robot can do.  For instance, if the terrain is not level, legs will drag on the ground or it will not walk at all.  The maximum speed is relatively slow and achieving it requires careful tuning of servo-level gains.  While it is more robust than nearly any other open loop 4 legged walker while standing up, even small disturbances can cause it to fall over.

While I’ve been working to some degree on quadrupedal robots for the last 5 years, it has been just about 1 year since I kicked up my effort a notch, with my post about improved actuators for SMMB.  I figured it was a good time now to produce a video summarizing what I’ve gotten done over the last year:

Concurrently, I’ve posted a “state of the project” text update on hackaday.io, just to get a wider readership.  If you’ve been reading here all along, there won’t be anything terribly new there, but it is a decent summary of where I stand.

My very first sun gear holder I machined myself was something of an artistic feat.  Each operation was re-run many times, and as a result the part was largely a one-off.  The final part properties were not really indicative of the final program.  My next step in my learning adventure was to up my Pocket NC game and get to a single reproducible program that would emit a part that I could use, then be able to run it over and over again.