I was inspired by Roger Rabbit's 3D printed linear actuators. I traded the ability for fine position control for scalability of travel only limited by the length of the timing belt and aluminium profile.
I'll add limit switches to tell the thing when to stop and maybe a middle position too if I can work it out.
Comment if you want me to add the 3D printed parts files (two plates and the gear).
The servo has been modified for continuous rotation. This means removing the internal potentiometer and the mechanical limit pin/stub. There are Instructables on how to do this.
I soldered four dupont connector wires to the three wires left when I cut the potentiometer off. One on either side and two on the middle (wiper) connection.
The voltage divider currently plugged in the dupont female connectors is made from two 10k Ohm 0.1% resistors. Interestingly, even with these tolerances the servo is not static when sent a PWM signal for 90 degrees. It settled to static around 94 degrees.
The voltage divider breakout cables allow you to try different forms of position feedback. Perhaps a digital potentiometer or a DAC based on other position input to the PWM-generating microcontroller?
The gear is only supported on one side, by the two metal bearings in the metal geared servo. To prevent too much shaft deflection (the belt is under tension to prevent gear slip) the bearings are spaced so that the belt tension and gear torque pulls the gear down and clamps the belt between the 608 bearings and its teeth. This greatly improves shaft support and belt engagement.
The frame plates will be developed to host the microcontroller and position feedback switches.