Here’s the approximately annual giant video update:
If you’re interested in any of the topics in more detail, I’ve collected links to individual posts for each of the referenced items below.
Thanks for all your support in the last year!
Announcement of moteus r4.3: Production moteus controllers are here!
With the new FD-CAN based moteus controllers I need a way for the raspberry pi to communicate with them. Thus I’ve got a new adapter board in house that I’m bringing up:
This one has 5 independent FD-CAN channels, an IMU, a port for an nrf2401l RF transceiver as well as a buck converter to power the computer from the main battery bus.
The prototypes were largely constructed by MacroFab, although I did the Amass connectors and the STM32s because supply chain issues prevented me from getting those parts to MacroFab in time.
After casting the feet, the final step was to join the lower leg with the 3d printed foot bracket. This I just did with some slow cure epoxy.
It seems strong enough for now, I was able to manually apply 10kg of load to a single leg while perfectly horizontal with no signs of stress, which should be good enough for a 4g 4 legged jump.
All the legs (and a spare) are now assembled with belts and a lower pulley ready to go on a robot!
Previously, I described the overall plan for my improved foot. To make that work, I needed to cast a 3d printed part into the squash ball such that it would likely stay attached during operation, be suitable rigid and yet damped, and do so repeatably.
To start with, I used a random single yellow dot squash ball with a hole cut in one side using a pair of side cutters. For the casting foam, I just used Smooth-On Flex Foam-IT 17, which is what Ben Katz originally used at least. Initially I just mixed up a batch, poured it in to a random level, stuck my bracket in and hoped for the best.
As mentioned long ago in my post on failing more gracefully, it was obvious I wanted to strengthen the lower leg and foot mechanism to remove the point of failure observed there. For now, I’m attempting to basically copy the original Mini-Cheetah foot principle, although with more 3d printing and less machining.
The basic idea is to print the entire lower leg in a single go laying on its side, so that delamination is unlikely. The foot bracket will be cast into a squash ball, then epoxied onto the lower leg.
One of the parts on the original quad A0’s leg that was prone to failure was the “knee stud”, a little cylinder that acted as the mating interface between the upper leg and the lower leg. It directly attaches to the upper leg, and has bearings that ride between it and the lower leg. The entire tension of the leg belt is born in shear by this part.
In the mk1 leg, this part was 3d printed with heat set inserts used to form the threaded holes. This mostly worked, although occasionally the stud could shear along the 3d printed lamination lines. Thus, for the mk2 leg, I’m making this part out of 6061.
Since the mk2 moteus servo has slightly different dimensions and a different mounting pattern than my original, I needed up update the full rotation leg design to handle it. The basic concept is the same, except for some in-progress work on the foot design which I’ll write up later. The only significant changes were that because of the mk2 design, access to the power and data connectors is much easier.
Here’s a brief CAD snapshot:
Finally returning back to other pieces of my quad roadmap, I finished getting an updated power distribution board ready for the quad A0. This board is one I had made many months ago and mostly brought up, but then didn’t quite finish. The r1 was when I first discovered my unfortunate stm32g4 pinout problems that doomed 3 of my in flight boards. The pictures here are of r2, which suffered from yet more pinout problems, resulting in more than my usual number of blue wires. Fortunately, identifying those problems here let me fix them ahead of time for the fdcanusb and moteus r4 boards.
One of the necessary pieces for bringing up the moteus brushless controller and for ongoing development with it is being able to communicate with the device on the desk. There aren’t many options for desktop FDCAN communication currently, and certainly none that are in the affordable range occupied by the [CANUSB family of devices](http://CANUSB family of devices) which I’ve used before and was very happy with. Thus I created “fdcanusb”, a USB to FDCAN converter that allows one to communicate with FDCAN devices via a USB interface using a documented protocol, no drivers necessary.
As the first part of the new moteus servo mk2, and continuing in my series of learning about CNC by building parts for the quadruped, next up I machined the input to the planet gears on my Pocket NC V2-50. This was a part, that for my quad A0 build, I used a 3d printed part in PETG as it is probably the least stringent part in the gearbox in terms of tolerances and load, although I still expect the plastic ones will likely wear and fail after some time with heavy use.
