My Motion Toy - yet another Stewart platform piston design

Another 6DOF motion platform design with cost being a notable design goal. But also actuator range and speed.



I don't have welding skills, but I have a 3d printer and a CNC that can cut wood. (And without the CNC, one could use Send Cut Send or OSH Cut.)

Still working on refining my piston design before building all of them.

Rough tour:

• AASD-type servos, see this thread for more info.
• Cut plywood and all thread to make the base. These takes the strong motion forces and routes them around the coupling and servo.
• 1616 ball screw. My calculations indicate I need to use 1616 or 2020 to reach my target speeds and forces.
• Angular contact bearings with 3d printed alignment/base plates transfer the ball screw forces to the plywood.
• 2040 aluminum extrusion and 1½" EMT tubing for the sliding parts. Strut channel doesn't have good enough tolerances.
• The 3d printed piece on the ball nut has a ton of heat set inserts for every screw and holds the guide wheels that engage with the aluminum extrusion. The EMT presses directly into the part for positive forces and two screws through the EMT hold it on for negative forces. (Ignore the rectangular cuts on the side of the EMT.)
• At the top I have three polyurethane-coated bearings to hold the EMT in alignment and another plywood plate.
• An anti-wobble part clamps onto a bearing at the end of the ball screw. It had little arms that were meant to flex, but they broke off easily. I probably should just reprint it without them at a larger radius.

Thoughts:

• Still need to figure out my u-joints. Pictured here with a stub and something to hook weight to for testing.
• Getting the right distances on the all thread to get the plywood plates parallel is a bit fiddly, but not awful.
• Thrust bearings (the kind that comes in 3 parts) are garbage. I'm having much better results with angular contact bearings.
• Heat set inserts are nice.
• The guide wheels between the ball nut and extrusion are presently a bit loose, in theory I can adjust it by rotating the off-center inserts inside the bearing, but in practice it's not so easy and maybe doesn't need to be perfect.
• I don't like how the bearings at the top work. It's fiddly to put together and adjust. Then, the print is weak enough that the bearings can bend away enough that things still rub. A simple plastic bushing didn't appear to be enough though. Ideas welcome.