Coming soon: Lasercar

It takes a 21st century laser to return motorized widgets to the medieval era.

I’m redesigning my basic robot car for the Glowforge — partly for convenience, partly just because I can. The laser cutter is way faster than a 3D printer for design iterations, even if the design itself  is more complicated and tends to need glue.

The two big issues for the wheel were getting all the interlocking parts to actually interlock, and getting a good fit with the standard gearmotor shaft. With the 3D printed version, you have to add an offset to the size, because the printing process tends to make holes smaller. With the laser-cut version, you have to subtract the offset because of kerf. (But of course the kerf isn’t uniformly predictable when cutting small objects, because the laser head doesn’t get up to full speed when cutting tiny little arcs and line segments.) It was nice being able to do a new test part in inkscape, upload it and have the result in a minute or two.20191019_1641544938995840075715437.jpg

It took three tries to get the hub cutout  just right, and a couple of iterations for the size of  the hub, which has to clear a locating pin on the motor. (I could get it smaller if I wanted to play with the axle pegs, but no obvious reason to do that.)

Oh, and that score on the inside of the wheel, which might want to be a bit deeper, is so that I can slip in a little ring of cardboard with optical-encoder slots cut out of it. I discovered last year with the 3D-printed version that some ostensibly opaque plastics don’t block enough infrared light to trigger an optical sensor. Oops.


You can see in the next picture how the laser-cut wheel compares to the 3D printed one, and get a rough idea of the 3d-printed body (which uses a half-length adhesive-backed solderless breadboard to provide structural strength). The laser version will use the wood for strength because it doesn’t take any more time (or plywood) to cut a stronger undercarriage.Replace 3d printing with laser for strength and build speed.

I’m going to need that additional strength because of a seemingly unrelated change, namely switching the programming language from Arduino to CircuitPython. Which means also switching from 5 volts to 3.3, only my inventory of sensors and motor driver chips and all that stuff is still 5-volt. So I need room on my solderless breadboard for some level switchers and voltage dividers, and even with the smallest practical controller board I’m going to have to use a full-length breadboard. On the plus side, I won’t have the battery hanging way out on each side.

I’e been doing all this work, btw, at the recently opened Pacem community makerspace, so I’m hoping to get a bunch of other folks interested in having little robot cars zipping around and interacting with one another. With a laser cutter, there’s also plenty of room for customizing and decoration.

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