The following instructable details the process of building a 4 axis positioning system (X,Y,Z+theta). While we leveraged this setup for an automata aquarium, it may be useful in your other projects as well. Anyway, our build targeted modified Hitec HS-55 servos (see this other shamelessly plugged instructable), but servos of similar size should also be usable with similar steps. Note that if another type of servo is used for this project, the CAD models for the 3D printed parts may need to be changed as well. This was part of a project for the spring 2012 Things That Think class at CU Boulder.
1/4 in. basswood
4 sub-micro servos modified for continuous rotation and position feedback.
Step 1: Laser Cut Parts
Using a laser cutter, cut the pieces from the attached file laser_cut.DXF out of 1/4 in. basswood. We recommend this material because acrylic and other plastics did not hold gear tooth shapes well when laser cut and, moreover, the basswood provided a good compromise between cut-ability and strength. The laser cutter patterns are designed for a beam width of 0.25 mm. The units for the .DXF file are in milimeters
Step 2: 3D Print Parts
The following parts need to be 3D printed. The units for the .STL files are in milimeters.
Step 3: Install Wooden Gears to Servos
Press the three gears onto the output shaft of three of the servos. If they do not press fit well, install a washer and screw to hold them in place.
Step 4: Add Sidewalls
Insert the 2 ft. long tracks and x rack into one of the rows on one of the side walls. The teeth on the rack should face the bottom of the side wall. Press the other sidewall onto the other end of the tracks and x rack. Ensure that the second sidewall has the same front-back and top-bottom orientation as the first sidewall, so that the x rack and both tracks are all parallel.
Step 5: Install Racks and Servos
First, place the cart on the tracks and x rack and install one of the servos with a gear into the servo slot on the bottom of the cart to hold it in place. Afterwards, press the y rack cap onto the end of the y rack. Then, place the y rack in the cart and install one of the servos with a gear into the servo slot on the top of the cart to hold it in place. Next, press the z rack cap onto the end of the z rack. After that, slide the z rack through the y rack cap and install the remaining servo with a gear into the servo slot in the y rack cap to hold it in place. Finally, install the last servo into the servo slot on top of the z rack cap. Be careful that the wires are correctly passed through their slot and are not pinched under the servo.