The moteus brushless controller I’ve developed for the force controlled quadruped uses an RS485 based command-response communication protocol.  To complete a full control cycle, the controlling computer needs to send new commands to each servo and read the current state back from each of them.  While I designed the system to be capable of high rate all-system updates, my initial implementation took a lot of shortcuts.  The result being that for all my testing so far, the outgoing update rate has been 100Hz, but state read back from the servos has been more at like 10Hz.  Here I’ll cover my work to get that rate both symmetric, and higher.

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.

Now that I’m making a lot of videos of machining with my Pocket NC, it was getting annoying setting up lighting for each one.  Thus I rigged up some LED strips in the interior of the enclosure.  Now I can shoot 60fps video any time of the night without having to set up external lighting!  Here’s to hoping a chip doesn’t short it out.

Workholding on the Pocket NC is still, well, a work in progress for me, and it is for many people.  There aren’t a lot of off the shelf solutions.  The machine does come with a mini-vise, which can hold a surprising amount, but it has some limitations.  For one, it isn’t referenced to the axis of rotation of the B axis.  Another, anything held in it can often be far away from the furthest Z travel available, resulting in the need to use extended reach tooling.

To demonstrate the dynamic capability of the full rotation quadruped, I figured I would start by doing some full machine jump tests to a relatively low height, just to show that it was capable.

Thus, I rigged up an open loop script which squatted a small fraction of the available distance, and then powered up at a relatively small fraction of the available maximum speed.  I don’t have the telemetry yet to extrapolate how high this will be able to go at maximum, but I think it should be a fair amount higher.  For now, I want to do some more instrumentation and walking testing (and have more spares) before I manage to break things by jumping really high.

After having used my PocketNC V2-50 for a while just sitting on top of the air compressor, I decided to try and improve its installation a bit.  For one, when the compressor kicked on or off, it would impart a significant vibration to the whole assembly.  Also, I needed a place to hold stock, tools, and intermediate parts.  Here’s a picture of my new setup.

The table isn’t particularly rigid, but at least it is now decoupled from the compressor.  The wire shelving below satisfies my storage requirements for now.

Last time, I had finished physically assembling all the motors for the updated quadruped with legs that can rotate freely 360 degrees.  After the long summer break, I powered up and configured all the servos.  Then, after setting up the gait engine for the new configuration (for which there are still a TODOs when the lateral shoulder offset is non-trivial as in this configuration), I was able to achieve some amount of walking.  Here is one of the first videos I took, without much in the way of tuning or work.  The control is a little wobbly still, but so far there are no signs of any mechanical failures as with the older design.

The next step in (re-)building the quadruped with a full rotation leg was getting all the motors ready.  I had to first install reinforcing rings on 6 of the motors:

Then, I needed to lengthen the power leads on 3 of the motors to serve as the lower leg joint.

I have been trying to improve the tool paths for the BE8108 gearbox sun gear holder.  The first time, I ended up slowing things down a lot and actually took some of the initial adaptive passes in several iterations as I fixed problems, so it wasn’t clear that any one iteration would be functional from start to finish.

So,  I tried it on a fresh piece of stock, with settings that I thought would resolve the pullout issues I had seen earlier.  Lo and behold, what did I find but more pullout!  It appeared to happen in exactly the same situations as before.  The adaptive clearance would leave a thin sliver of material, then “round it off” very rapidly, resulting in a large chunk of sliver hitting the mill at once.  Increasing the minimum cutting radius and tolerance helped reduce the problems some, but didn’t get rid of them entirely.

After doing my first cuts in aluminum, I wanted to actually try and make a real part, to prove that the Pocket NC v2-50 was capable of making things that I can actually use.  My first attempt, was the same part I did my first aluminum cuts in, the sun gear holder from the BE8108 planetary gearbox.

This part attaches to the rotor, the sun gear, the position sense magnet, and has bearing interfaces to the planet input and the back housing.  While not terribly big, the number of features and mating surfaces is relatively large.