Tag Archives: fixture

Quad feet construction fixture

The quad A1 was the first robot I built with foam cast feet.  When I did the first feet, I jury rigged a fixture from some old toilet paper rolls to hold things in place while they were curing.  When I went to rebuild with my most recent leg geometry, I figured it was time to get at least a little more serious.  Thus, my new leg casting fixture:

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When an insert is cast into place, it is set on one of the trays, the tray is inserted into a slot, and then a weight can be placed on top and constrained by the fixture.

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This makes the casting process more repeatable and faster as I scale up production.  As a bonus, it can also be used as a fixture to epoxy the lower leg to the insert:

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Leg zeroing fixture

As part of provisioning a quad A1, or anytime the mechanical configuration has been changed, I need to go and record where the zero position of all the joints is.  The “0” position for the software now is with the shoulders perfectly horizontal, and the upper and lower leg sticking straight down.

Up until now, every time I’ve done this it has just been by eyeballing and with lots of foam and bubble wrap to shim things into place long enough to record the level.  Sometimes I had to go back and try a few times, as even determining when something is straight is not, well, straightforward.

So, I made two new fixtures to help with this process:

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One that rests on a flat surface and supports the shoulder to be exactly level, and forces the upper leg to be exactly at a 90 degree angle.  This assumes the robot is flipped over on the same flat surface.  The second snaps between the upper and lower leg, forcing them to be exactly straight.

With these two fixtures, I was able to get repeatability of my calibrations down to less than half a degree, which should be good enough for now.

 

Programming and testing moteus controllers

Like with the fdcanusb, I built a programming and test fixture for the moteus controllers.  The basic setup is similar to the fdcanusb.  I have a raspberry pi with a touchscreen connected via USB to a number of peripherals.  In this case, there is a STM32 programmer, a fdcanusb, and a label printer.  Here though, unlike with the fdcanusb fixture, I wanted to be able to test the drive stage of the controllers and the encoders too.

My solution was to create a mechanical fixture that each board slots onto, with pogo pins that connect to test points for the phase outputs.

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While it doesn’t make as good a connection as the solder through holes normally used to connect a motor, it is good enough to verify that the controller works.  As a side-bonus, it also makes it trivial to test that the absolute magnetic encoder works properly.

This video shows how the programming and testing process works, and walks through testing a few boards.

Programming a lot of fdcanusbs

To get ready for the initial limited release of fdcanusbs, I needed to program a whole bunch of them.  Further, I wanted to be able to scale up a few factors of two without being too annoyed with manual steps.  Thus, enter my minimal programming fixure:

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It isn’t much, just a raspberry pi 3b+, the official 7″ rpi touch screen, a STM32 programmer, a “fixtured” fdcanusb to drive the device under test, and a label maker.  The touch screen is mostly there to display the results if anything goes awry, as in normal operation there is just one button to push.  The final cycle time to program a fdcanusb and install it into the enclosure is around two minutes, which is good enough for now.