On the mjbots discord, people are often looking for the cheapest possible way to command and monitor a moteus controller. One possible solution that comes up over and over again is the CANBed-FD board, as sold by Seeed Studio (and others). I decided to get one of these in house to see if I could make it work:
The first thing I figured out was that the DB-9 connector used a non-standard pinout for CAN_L and CAN_H. I just switched to the terminal block connections instead of the DB-9 to get around that. For the software, I decided to use the acan2517FD Arduino library, as it was quite a bit more robust and featureful than the one provided by Longan Labs.
With this in hand, I was able to get the Arduino to send properly formatted CAN-FD frames that moteus would receive. However, as it often does, the problem came when receiving. This Longan Labs board uses a 20MHz clock for the MCP2518FD onboard, which means that it is only *just* able to do the 5MHz CAN-FD clock rate that moteus requires, and there is no margin for actually being able to synchronize to a slightly skewed bitrate using the sync jump width. Because of this, I was not able to get the device to receive data from a moteus controller except by nudging the bitrate of the moteus controller around by fractional percents manually, and then it only worked for a short time before temperature, or humidity, or whatever, drifteed it out of range.
If someone finds an Arduino board that uses a MCP2518FD with a 40MHz clock (or a 4MHz clock that uses the built in PLL), let me know, as I expect that should be able to work fine. That is the configuration used by the Seeed Raspberry Pi CAN-FD adapter, which has 2 MCP2518FDs with a 40MHz clock and it has been demonstrated to work with bit timings listed in the moteus reference documentation.