Updated moteus test fixture

I documented the first test fixture I built for moteus some time ago. As the shipment volumes have gone up, the fixture became something of a limitation, and also was a little problematic in a few ways.

The old “state of the art”

First, it relied on attaching 3 connectors by hand for each test, which was a decent fraction of the cycle time. Second, the pogo pins it used were non-replaceable, and also connected only to the debug phase wire test vias, which were tiny. They wore out relatively quickly, and replacing them required building a whole new board. Finally, since the pogo pins were PCB mounted, a PCB needed to be printed for any change in the pin locations or which pins to probe.

New fixture

Enter the new fixture:

From the side
With no board installed
Without the top platen
Lid raised, showing board contacts

This one uses modular test probe receptacles with replaceable tips, so that the tips can just be swapped out as they wear. These don’t appear to be available in an inexpensive manner in the US, but aliexpress has many options with 5 or 6 probe types in many sizes.

Second, the receptacles are all aligned with a 3D printed baseplate and platen to align them before contacting the PCB. This works alright down to the 1.5mm spacing test points on moteus, although that pitch is pushing what can be achieved with a 3D printed part.

Third, power, CAN, and the debug serial connections are now all probed from the bottom, so only one connector, the SWD programming port needs to be connected by hand.

Finally, the whole structure, including the top clamp is 3D printed now, which makes it potentially possible to do top probing and more easily adjust the dimensions.

With this new fixture, my cycle time for a test is around 60s. At that point, the time spent in the test program is about the same as the time it takes to unpack and package up the boards, so it isn’t really the limiting factor any more.