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Alternative gear and worm gear for Inmoov Robot shoulder

by ForrestHiggs, published

Alternative gear and worm gear for Inmoov Robot shoulder by ForrestHiggs Feb 9, 2013


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I found that the original gear and worm gear pair for hairygael's Inmoov Robot's shoulder seemed to bind a bit, so I designed a pair which seem to operate a bit more smoothly.


PLEASE NOTE! II have modified the involute profile gear and worm gear slightly. The worm gear was modified a bit to turn more freely and the involute profile gear now includes the slot for mounting the potentiometer which I had forgotten to include in the earlier version.

I printed these parts in ABS on an UP! Pro 3D printer at normal print speed and using a .3 mm layer with an infill level one step below 100% infill, viz, almost solid.

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Would this work in the bicep gear box?

Zviangi: I found that I could "mirror" the gear and worm using Netfabb to reverse the direction of rotation. Works fine.

the direction of rotation of this worm and gear is different, than the original one. This causes the servo to have reverse angle, no matter which side you place it. changing the pot wiring does not help, because it starts to rotate in wrong direction. Can you modify these gear an work to have reverse direction of teeth?

I just printed worm and gear and found that the worm is not going into PivCenter, did you modify PivCenter by hand, or have made modification also for PivCenter STL?

a correction, I saw, the shoulder PivCenter is mofied for the alternative PivWorm, Bicep is the same

I printed one and it was a good fit the only problem was after bedding in the worm gear i got wear on the shoulder of the worm and the housing looks like the angle of the teeth put a side load on the worm causing wear. I used a cordless drill to bed in the gears if you use a motor fixed to the housing then the worm wont float as much

like post a picture on the weekend

Great, I'm glad to see remixes. First the cylinder of the gear is now round when mine was with faces which had to be smoothed. Does the angle on the gear helps? When I used mine I didn't have bind, but no slack either. Grease is really important because there is pressure on the parts. Plastic parts will worn with time, that is for sure.

The angle of the teeth needs to match the pitch of the worm gear unless you want backlash or binding. I was curious, though. It seemed like the pitch angle for the worm gear was about 20 degrees while your involute profile gear had a pitch angle, I estimate, of about 32 degrees. I reset both to 20 and wound up with a gear radius of 31.5 degrees to get a no-backlash fit. Was there some design protocol you were using there or did you develop that gear pair intuitively?

I wondered why the faceting of the cylinder drum was so low resolution. Which 3D CAD package are you using?

The low resolution faceting is a choice I make when creating my parts in Blender, I often end up re-faceting some parts by hand, when the structure is a bit complexe. So, when creating an initial circle, I always use a 16 face base.

I designed it intuitively. I estimated the friction point on the worm gear would be at it's center on the pitch, no matter which way it would rotate, then I designed the gear teeth to fit in as deeply into the worm gear to get the most flat friction on it.

I have been using openscad version of Sylvitch


Let me know how your improvement reacts when it is loaded with the rest of the arm and servos

Worm Drive, Non-Throated
by syvwlch

I tend to use a combination of Art of Illusion and Netfabb. I am fond of AoI simply because it is so easy to write scripts when you want to design something special.

I wondered what that rectangular hole was for. I plan on a redesign of the gear and to see if I can make use of the 32 degree stress angle you used with yours in conjunction with the sloped teeth that make mine fit better.