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Unread 03-01-2005, 13:10
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Bill Gold Bill Gold is offline
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Re: Worm Gear Gearbox

Like Cory said earlier, the team I was on last year (258) used a CIM to power our shoulder joint, and the other CIM to power the elbow joint in our arm last year. Each CIM ran into its individual gearbox, and then powered their joint via #35 chain/sprockets. In each gearbox the CIM was reduced with spur gears at a 3:1 ratio, and then reduced another 60:1 with a 60-tooth worm gear and a single thread worm (worm ratios being # of teeth in the gear / # threads on the worm), and then there was a sprocket reduction of 4:1 to the joints.

The cast iron worm gears didn’t crumble, and the only problem we had was due to some “over-engineering while under-thinking.” Long story short, we use nuts to hold the worm in place on its shaft, but didn’t think about the nuts loosening up due to the rotation of the shaft (which they did). So, after a while the nuts would back up, and when we tried to rotate the arm with all of our robot’s weight behind it (like trying to “chin-up” to hang) the worm would slightly slide out of place, and end up stalling the gearbox/motor. If we had just machined an aluminum spacer instead of using those stupid nuts, that arm would have perfectly accomplished all it was designed for. Oh well, live and learn…

Our worm gears were ordered from Martin Sprocket…
10DP 60-tooth worm gear (W1060)
10DP Single Thread Hardened Worm (WG10)

http://www.seadawgs.com/1.JPG
http://www.seadawgs.com/2.JPG
http://www.seadawgs.com/3.JPG
http://www.seadawgs.com/4.JPG
http://www.markrobot.com/gallery.php...ncoln%2F17.jpg
http://www.markrobot.com/gallery.php...ncoln%2F41.jpg
http://www.markrobot.com/gallery.php...ncoln%2F46.jpg
http://www.markrobot.com/gallery.php...ncoln%2F42.jpg

I’ve also seen many other uses of worm gears in drivetrains and other robot mechanisms. They can be great for situations where you don’t want backdrivability, or for a huge reduction in a relatively small amount of space. As with any gear-to-gear setup, be sure you have the ability to machine your gearbox fairly accurately, or else you’ll get either binding or huge backlash (or no gear contact at all). If you have any questions about these gears I’d suggest checking out an informational .pdf that Boston Gear has (http://www.seadawgs.com/GT.pdf), or go into Borders/Barnes & Noble and skimming through (or just buying) The Machinery’s Handbook. There’s tons of great stuff in both of those.

I hope this helps.

-Bill
 


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