Robust lead screw and thrust collar for InMoov bicep
by ForrestHiggs, published
I noted that the lead screw for the InMoov robot's bicep tended to experience shear failures rather regularly when I was calibrating the elbow flexure. Rather than replace it with a steel lead screw, I decided to design a more robust plastic lead screw instead. The diameter of the lead screw has been increased from 12.5 mm to 25.5 and the thrust collar enlarged to seat the new leadscrew. The pitch and length of the lead screw are unchanged.
In order to accomodate the bigger lead screw in the rotgear it was necessary to raise the hole that seats the thrust collar axis on the higharmside part by just over 11.5 mm. I did this by plugging the old hole and locating a new one above it.
A walkthrough showing how the new lead screw seats in RotGear. http://haptictelepresence.blogspot.com/2013/03/seating-new-larger-leadscrew-in-bicep.html
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The fit between the lead screw and the thrust collar is tight. Smearing petroleum jelly on the lead screw and working it back and forth through the thrust collar a few dozen times will leave you with a smooth running fit that requires very little torque to operate.