A fun and functional 3-axis hybrid parallel robot that fits on your desktop
Made a lot of progress assembling the initial prototype! New hinges are working great and are much sturdier.
Changing hinges required a redesign of several parts. Took several days but they are done and being laser cut at MakeIt Labs in Nashua, NH.
Finished 3D printing the first TR8 MakerWheel prototype for use with a TR8 x 8(P2) screw (for those not familiar with the terminology, this means an 8 mm diameter trapezoidal thread with 2 mm pitch and 4 starts). TR8 screws are typically used as lead screws. We are using one for the z-axis. However, we are also looking at using them in the rack and pinion actuators controlling the x and y axes. The screw acts as the "rack". Four idler MakerWheels (like the one shown in the photo) support each screw and allow it to translate along a path parallel to the axis of motion. A MakerWheel pinion coupled to a NEMA 17 stepper motor controls the position of the screw.
Standard M8 threaded rod is also being explored as a lower cost option. In general, TR8 screws are more expensive than M8 threaded rod but provide much better quality and precision. They also provide a larger thread pitch (TR8 pitch is 2 mm vs. 1.25 mm for M8) and a squarer thread profile. From my experience, larger pitch threads are easier to 3D print and provide better strength.
The attempt at using living hinges for the leg joints was not successful. No worries, replacement hinges (shown on the left) have been selected and will be integrated into the next design revision. The new hinges are larger and should provide a significant increase in rigidity. They also cost less. Can't wait to test them out!
Started assembling the frame, z-axis and legs. So far everything is fitting together nicely. The living hinges seem to work well but I am a little concerned about their ability to hold the weight of the mobile platform when it is fully extended. Only one way to confirm whether they will work... keep building.
Laser cutting of the initial prototype parts was completed at MakeIt Labs in Nashua, NH.