This is a 3D printed version of the "Spinner Lab" from the Modeling Physics Curriculum. This works great for collecting position vs. time data for an object that is accelerating constantly. In this case, the Spinner, accelerates down two metal poles (1/2 EMT conduit) that are propped up by a textbook on one end.

To make the Spinner, print one copy of the disk and two copies of the "T"s. The Tees are called that because the original version of this spinner was made by cutting a disc out of plywood and then glueing a golf tee to either side. The taper of the golf tees acts like a train wheel and corrects the motion of the disc so that it stays in the middle of the track.

I print these materials out of PLA at around 15-20% infill.
The Tees are designed to be a tight press fit into the disk. However, if you print them at 100% size, they likely won't fit into the holes. I print them at about 98% of their designed size (just re-size them to 98% when slicing). You should print them out and test the fit before printing a bunch, then adjust the scale of the Tees. You want the Tees to fit tightly in and not come out easy. The Tees should come out, however, if the spinner is dropped from table height. My first version of this was one solid object and the parts sticking out kept breaking when students would accidentally drop it. This version doesn't break, usually one tee falls out when its dropped and then you just pop it back in. Over time (multiple years), I sometimes have to print a few new tees because they get worn by popping in and out (usually for fun, not dropping).

I also wrap a single layer of duct tape around the outer part of the tee (the thinnest section) so that the tee grips the metal track and doesn't slip when accelerating.

The "bar holders" are sized to fit 1/2 EMT into. I wrap a layer or two of electrical tape around the ends of the bar to make them a tight fit.