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:

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.

While continuing to bring up the r4.1 moteus controller I reached a mini-milestone where it spun a motor for the first time!

Another step in my plan for the next revision of the moteus servo mk2, is an updated controller board.  As mentioned in my roadmap, I wanted to revise this board to make improvements in a number of domains:

• Communications: Now instead of RS485, the primary communications interface is FD-CAN.  This supports data rates of up to 8 Mbit and packet lengths up to 64 bytes.  The header is nominally at the original CAN bit rate, but I have no need to be standards compliant and am running very short busses so I may run everything at the higher rate.
• Connectors: Now there exist power connectors, in the form of XT30 right angle connectors and they are also daisy chainable like the data connectors.  Additionally, all the connectors exit from the bottom of the board to make routing easier in configurations like the full rotation leg.
• Controller: This uses the relatively new STM32G4 controller series.  It is lower power than the STM32F4, supports FD-CAN, and also supports closely coupled memory, which may allow me to improve the speed of the primary control loop execution by 3 times.
• Voltage range: This board now has 40V main FETS, with all other components at 50V rating or higher.  Thus it should be safe with inputs up to 8S (34V or so).