All of the current lab members use 9 mm diameter foam balls for behavior, although in the past some people have used 6 mm balls, and also used different plastic materials.

We now make the foam balls ourselves. We obtain the foam from General Plastics, by requesting a “sample kit” of blocks of various foams. We usually use FR-4615 foam (although we have tried FR-4510 in the past - this is a more porous foam than FR-4615). Foam samples are stored in the behavior hardware drawer in the main lab (under the soldering station).

The most up-to-date instructions should be placed on this repository, so we can share the steps and materials more easily: https://github.com/wilson-lab/treadmill-ball-grinders/

Regardless of the material the ball is made form, you will need to paint a pattern on the ball to use it with FicTrac. There needs to be a high contrast between the pattern and the ball, so we usually paint the patterns black (either with matte painting and a small paintbrush (The Pelikan Tusche A Drawing ink has a great contrast), or with Sharpies). The pattern needs to have distinctive local features for FicTrac to work, and this can be achieved by painting letters and/or numbers into the ball.