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Unread 02-05-2008, 20:13
ajlapp ajlapp is offline
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AKA: Anthony Lapp
None #0118 (Team RUSH and Robonauts)
 
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Re: How much torque can the Dewalt Trannies take?

As stated in another post Team RUSH is working on a short whitepaper about the engineering development we went through this season with our Dewalt trannies.

First off let me say that prior to this season we had zero Dewalt failures. They are truly robust and easy to implement.

That said, I'll give you a short run down of what we saw in general.

The format we used was two cims into a dewalt via about a 2.2:1 reduction....this then directly drove a 6" wheel with a custom shaft. Previous version had a final drive via another chain and sprocket...this increased the torque directly inside the transmission about 3 times..

We made this custom shaft from 1045 key stock available from mcmaster. Our original failure was to twist the double d off the shaft directly inside the dewalt.

We switched to a 4140 shaft...same result. We then made another shaft that threaded onto the dewalt shaft and was cross pinned. We managed to break a few pins, but the shaft strength issue was solved.

The dewalt then started dropping pins and gears from the inside of the planet set.

After much analysis and some dissection of various dewalt trannies we found the toughest variant sold in the 18v line. I don't recall all the suttle variations, but there are a few.

We then modified the second stage to hold larger pins. We also bored the planets to match.

The final failure was to actually spin the transmission carrier inside the yellow dewalt housing. Another fastener and pin solved this problem.

We also chopped the max pwm output of the system to staop the driver from being able to deliver max torque into the system while stalled or turning. This helped a lot, but cost us some speed on the back stretch.

Final verdict...the system works well now, but the edm process used to bulk up the trannies gets away from the ease of use. Another section of chain, a final drive stage or some other means of soaking up the torque spikes could make this system perfect.

p.s. 118 does put 6 motors through one dewalt, but they have tons of chains all zapping some of the torque way before it ever gets back to the dewalt; and they never go in reverse.
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Anthony Lapp
FIRST Engineering Mentor
Owner/Operator 221 Robotic Systems
221 Robotics Systems - Quality Hardware, Made in the USA
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anthony@221robotics.com
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Team 1 --> 94 --> 68 --> 221 --> 857 --> 27 --> 118
Design Engineer/Fabricator and 17 year vet
Team Rush (FRC27) and Robonauts (FRC118)

Last edited by ajlapp : 02-05-2008 at 20:17.