The perils of technical videos is that they can become out of date pretty quickly. For the moteus getting started guide, it has amazingly held up pretty well, but enough has changed since 2021 that it is time for a new one. Now we can use acceleration and velocity limited commands instead of the deprecated stop position and get nicer 4k b-roll for all the intermissions. Everything in the old video, and in this new one, is applicable to both the moteus-r4.11 and the moteus-n1.

Back last year, I walked through bisecting and debugging an annoying problem that caused the STM32G4 ADC on the moteus controller to exhibit higher than expected noise in result largely to either the exact placement in flash of the initialization code, or to the exact timing of the initialization. While the immediate glaring sharp edge was removed, the resulting performance still was confusing to me, and looked like it was not yet optimal. Further, a moderate percentage (2% or so), of production boards failed end-of-line tests related to the current sense noise in ways that were hard to fix by swapping components. Because of this, I wanted to dive in and investigate further. This is that process.

If you look around online, there are lots of examples of PCB test fixtures used to perform end of line testing. In the low to medium volume scale, nearly all of these are either clamshell or 2 side affairs, where probe pogo pins or interfaces are connected to the bottom and top of the board.

When developing the moteus-n1, one of the challenges was the number of right angle board edge connectors it has. Those right angle connectors are what allow it to maintain a very low overall stack height when installed in applications, but are also much harder to perform testing on, since by definition the access points are not vertical. On the base n1, there are 6 total right angle connectors, 2 on each of 3 sides, and future variants may have additional bottom side CAN and power connectors populated to make 8 total right angle connectors.

I don’t normally post about moteus firmware releases, but there have been many in the last few months that fix some long standing bugs and regressions. First, the current release as of this post is:

• github: 2023-06-22

With that out of the way, here some of the fixes:

Position drift with non-unity gear reduction

It is embarrassing how long this issue has been outstanding, but ever since the flexible I/O system was introduced, there has been an issue where if the gear reduction was configured to a value other than 1, then the output position would drift from the source encoder over time. If control was not active, you would see the position drift, and if control was active, then moteus would report the correct position, but the actual position would drift.

This is a short and sweet post. The moteus-n1 as previously announced in beta form is now officially available at mjbots.com!