DeWalt Transmission Problem

[Kilroy0846]

Our team recently purchased two brand new DeWalt transmissions and interfaced them with the KOP globe motors. One Drives a belt and the other drives a chain with idlers at the bottom. They are both attached to arm fixtures, one with minimal weight and the other with a substantial ammount of weight. The transmissions work great lifting our the armatures, however when letting them down they tend to jump. The transmission attached to the lighter weight jumps almost un-noticeably. The larger one however will not turn when the torque is set to one and jumps once then breaks the torque when set to 21. We have tried surgical tubing to relieve the weight from the transmission, however when it gets towards the top and the tubing slacks we have the same problem.

Has any other team experienced this problem? How did you solve It?

[ajlapp]

That sounds like back-drive pins. Try removing them and see if your situation improves.

The NBD paper discusses the feature. I seem to recall having this issue in 2005 with our arm. The back-drive pins caused problems while lowering the assembly due to excessive loading.

[Kilroy0846]

If we remove these are we going to loose the ability to hold the arm in position after lifting it?

[ajlapp]

Yes, removing the pins will allow the transmission to easily back-drive. But that isn't necessarily a bad thing.

A common practice is to counter-balance your arm, then use a pot or encoder as a feedback signal. Software can then understand the arm/joint location and use the motor to keep the structure located in space.

There are many examples of this on chief....a tag search for "arm" should give many examples of how teams have previously built arm-like systems.

This RUSH Bot from 2005.....you can see the gas springs on the lower joint that help counter-balance the weight of the arm system.
http://www.chiefdelphi.com/media/photos/20302

Chiefdelphi from 2000 using gas springs as counter-balance and dampers.
http://www.chiefdelphi.com/media/photos/12954

[Josh Murphy]

Is the motor itself jumping inside or is it the chain/belt? We did have this problem about a week ago and we are using the globes to move some pretty light material. We were trying to save weight and didn't put the black rings on them that control the torque. They would not move what we wanted them to when we put load on them so I put the black rings back on and set the torque on the arrow, not on any numbers and we have been fine since.