The Turret

The first step in the construction process was putting together the turret. We designed it to have two of the hobby servo motors connected orthogonally - the one on top to hold the wheel of markers and the one on bottom to actuate the markers back and forth. We used maker beam from the robotics kits to create the structure for the servo motors and laser cut acrylic for the hub mount and to secure it to the base. The marker wheel started as a single sheet of acrylic with rectangular slots for the markers, held on with zip ties, and has evolved into a sandwich consisting of two pieces of 1/8" acrylic (1/4" acrylic was too heavy for the bottom servo to reliably pick up and down).

Base and Roller

After cutting down the tube to the proper size, we laser cut caps out of 1/4" acrylic to be press-fit on the ends of the roll with tabs. Originally cut with a Dremel plunge cutter, the edges of the tabs were gradually filed away until a tight press-fit was achieved with the cap. The caps also had holes laser cut into them that matched up with the tube clamps in the tetrix set.

Once the axle for the roller had been constructed, the base was built out and guides were laser cut to hold the center of the roller at the point of forward contact of the marker turret. A v-shaped design was chosen for the axle holders to minimize the number of contact points and friction force (bike chain grease was added after to help the motion as well).