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!

Just because I’m generally looking for workholding solutions for the Pocket NC, I recently picked up a vise designed for it from wcubed.co.

Unlike the stock vise that comes with the PNC, this has two movable aluminum jaws.  It can probably hold with greater force than the stock vise, since there is a larger contact area, although the screw mechanism doesn’t necessarily apply the force all that uniformly.  Also, since both jaws are movable, you have to take some care to either manually center things, or do some edgefinding, which isn’t terribly easy on a PNC.

As mentioned previously, I made up some soft jaws to hold 4in round stock in a 6" vise.  My goal was to prepare stock for workholding on the Pocket NC v2-50 to machine prototypes of the front and back housing for the reduced weight moteus servo mk2.

Now, I’ve used those soft jaws to trim down both pieces of stock to the correct length, bore a center hole, and in the case of the front housing, remove a bunch of additional material in a more expeditious manner.  There’s not much more to it than that, so here’s the video:

While working to build the reduced weight moteus servo mk2, I got tired of hand machining the first operation on a manual mill and lathe for the front and back housings.  It was necessary, primarily to enable workholding on the PocketNC v2-50, but also because it allowed me to remove much of the excess material more quickly than could be done on the PNC.  So, I got trained up on the AA CNC Bridgeport and went to town.

Before ordering a bigger batch of the new moteus r4.1 controller, I wanted some assurance that it would be able to run for an extended periods of time under representative loads while not breaking or having thermal issues.

When I did this for the r3.1 controller, I had 2 motor joints and a planar leg built and did a jumping endurance test.  I could have done that now, but building up a leg fixture was more work than I wanted to mess with at the moment, so I went with a simpler approach:

While working to build a weight reduced moteus servo mk2, I reworked my outer housing CAM to do all the machining on the Pocket NC v2-50.  For this part I didn’t necessarily need any challenging workholding and since I could get the stock in tube form, there wasn’t an inordinate amount of material to remove either.

The one challenge is that when mounted in the Sherline Chuck, the mill can’t actually reach all the way to the edge of the part without hitting the X travel limit (which is why most of the other 100mm diameter parts I do are fixtured slightly off-center).  In this case I tackled the problem in two iterations.

I introduced the fdcanusb previously, now I’ll describe some of the process and challenges in getting it to work.

Hardware

My initial challenges were around the PCB design and manufacturing.  To begin with, my very first revision was sent out for manufacturing with the same incorrect pinout as the moteus controller r4.0 and thus was only really usable as a paperweight.  Second, the supply of STM32G474 chips seems to be spotty now, so for r2 I had to scavenge chips from the boards that had broken pinouts.

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.

Last time I had an actually hard problem…, a mis-aligned stack which caused randomly misbehaving software.  This time, I had a more prosaic problem.  One that while not necessarily as interesting, was even more time consuming and frustrating.

The serial port wouldn’t work.  I had copied the module I used for DMA based receive and transmit from the STM32F4 and it just wasn’t working.  Nothing was written and nothing was received.  I carefully inspected the software many times.  I looked at the registers in the debugger and nothing seemed obviously amiss.  I read the datasheet to look for subtle differences in the theory of operation between the STM32F4 and STM32G4 but came up empty.

In my continued quest to bring up the STM32G4 for the moteus controller r4.1 and other efforts, I get to discover and learn about the million and one ways in which things don’t work on my path to find the one or two ways in which they can work.  I recently had an interesting enough problem that it is worth it to signal amplify google searches on the matter for the next unfortunate soul.