To verify that I could make FD-CAN work in the next revision of the moteus controller, I made a simple desk setup between two NUCLEO-G474RE boards.  I started by soldering up some breakout boards for the TCAN334G CAN transceiver I’m planning on using:

And then wired those up with a lot of jumper wires:

After a fair amount of fiddling, bisecting against the ST CUBE example project, and fixing some problems with my STM32G4 support in rules_mbed, I ended up with some 16 byte CAN frames being sent and received with a data rate of ~4Mbit.

While working on the next revision of the moteus controller, I started by bringing up a software toolchain on a NUCLEO-G474RE board.  Unfortunately, even the most recent mbed 5.14 doesn’t yet support that processor.  Thus, I have a half-baked solution which pulls in the ST CUBE sources for that controller into the mbed tree as a patch.

https://github.com/mjbots/rules_mbed/blob/master/tools/workspace/mbed/stm32g4.patch

The patch only implements wrappers for the things I care about, so it isn’t a complete solution. Since I am not really using any mbed libraries anymore in any project, that isn’t a whole lot.  Right now I’m just using it for the one function that sets up the board, a linker script, and the pin mappings.  I will probably eventually just make a rules_stm32 and ditch mbed entirely but for now that is more work than it is worth.

While bringing up an STM32G4 for the new revision of the moteus controller, I wanted to be able to flash and debug the system, and thus needed a working OpenOCD installation.  The NUCLEO-G474RE board has an ST-LINK-V3 debug interface, which no released version of OpenOCD supports, although thankfully that is working just fine at HEAD in git.  However, to make the STM32G4 work I had to pull some patches from the sysprogs/openocd tree.

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.