Floating planets robot joint - Apr 15, 2019

This was one of those projects that you get in your head and at some point just have to do it.

It is a little on the heavy side (147 grams) but the advantages are

• High speed
• High accuracy
• Anti-backlash
• Backdriveable
• High holding torque

TODO: Add encoder for servo control.
The idea was to drive all 6 motors in the same direction for torque but when approaching the set-point reverse a few motors and provide backdriving to prevent over correction.
You can drive 3 forward and 3 backwards to hold position.

Motor: ebay 3v 30RPM gear motor   You will need 6 of these.


CAD view (both sides are the same)

Not my best CAD work but as a prototype it worked so much better than expected.

See it in action

It is quite powerful but i forced it by hand too many times and striped the planets. The planets will need to be better than PLA to be useful.

Some construction photos

Additional materials used

• 4x 8mm x 30mm wood dowel
• 1x 8mm x 78mm wood dowel

Downloads

parts.zip	STL parts ready to 3D print
fusion_360.zip	Fusion 360 design files

I hope someone finds this useful

Thats all folks