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Robust lead screw and thrust collar for InMoov bicep

by ForrestHiggs, published

Robust lead screw and thrust collar for InMoov bicep by ForrestHiggs Mar 21, 2013

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Summary

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

Instructions

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.

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can it be used also for a shoulder?

Okay. I fixed the clash problem and think this might be worth trying now. :-D

DO NOT USE RIGHT NOW. AS GAEL SUGGESTED, WE DO GET A BINDING PROBLEM WITH ROTGEAR. I AM WORKING ON A FIX ON THE THRUST COLLAR WHICH SHOULD CAUSE A MINIMUM OF CHANGE NEEDED.

Good luck with the PLA. I've never been fond of it, myself.

If you get it working and everything works fine, please let me know... Printing parts in PLA and I am sure the extra strength provided by this will be extremely helpful to us

I set the overhang limit to 40 degrees instead of the usual 45, so there was no support required for the threads on either the lead screw or in the thrust collar. It did make the undersides of the threads a bit rough. That's why I greased the lead screw and worked it in the thrust collar for a little while to knock off the rough bits.

If you decide to use this you might want to put those little cradles under the rotation axle ends again. I took them out originally because the UP! printer creates them automatically.

I can't say for sure, but I suspect that the HS-805BB will stall without breaking this lead screw first.

I'm not sure about the binding part you speak of. I'll know more when I've figured out how to get the servo/potentiometer that drives it working properly. :-)

Good goal! This is interesting indeed, reducing the torque to operate is great. Strengthening it is also good! Can you still print it without support? My main concern is: doesn't it bind into rotgear's sides when operating up? Hopefully not because this is cool.

It doesn't bind into rotgear's sides nor does it require support to print as such.

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