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Unread 30-04-2008, 11:36
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Re: How much torque can the Dewalt Trannies take?

From talking to 118 they said they never had an actual problem with the gears in their dewalt transmissions, but they had problems shifting them with all the power.

We are planning on prototyping a transmission this summer with 2 cims into 1 dewalt which I think shouldn't be a problem at all.

One thing that 118 said is that all of the cutting on the dewalt housings and things like that needs to be very precise for them to work right.
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Unread 30-04-2008, 12:19
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Re: How much torque can the Dewalt Trannies take?

Perhaps Dennis from Team 27 could shed some light.
I think they found the limit this year, as Team 27 Team Rush was replacing Dewalt trannys after a few matches due to a catastrophic failure of some part in the system.
Maybe Den could figure out what type of load and torque they were seeing and let everyone know what the the limit is.

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Unread 30-04-2008, 16:26
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Re: How much torque can the Dewalt Trannies take?

I'm not necessarily the best person on this subject but as far as I know we don't have any real numbers on the limit of the dewalts. Though the failures appeared to have similar simptoms, we managed to cause a different failure almost every time. This was running two cims through the dewalts on a 6 traction wheel drive (6 inch andymarks) with the center wheels dropped.

edit: originally we did break a few drive shafts but then we managed to chase the failures into the transmissions themselves
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Last edited by Josh Fox : 30-04-2008 at 16:28. Reason: further input and spelling, grammar and such
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Unread 30-04-2008, 17:01
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Re: How much torque can the Dewalt Trannies take?

Robodox also used 2 CIMs driving 1 Dewalt in a setup very similar to RUSH.

We used a 3:1 belted reduction from each CIM to the input of the Dewalt. The output of the Dewalt directly (via a coupler) drove the center wheel of a 6WD 1/8" center drop drive train.

(RUSH used a slightly lower geared reduction before the Dewalt.)

Some observations:

The Dewalts are planetary transmissions. As such, they have a considerably lower efficiency than a gearbox using only spur gears. (They also take up less space for the same reduction.)

You've got to make sure you hold the actual transmission really well. The original housing from the Dewalt drill is best for this. We found that our major point of failure was the actual transmission spinning inside the housing (we didn't use the entire drill casing - our mistake!) We found this out in testing and never had a problem in an actual match.

Shifting is not always smooth - especially using a single servo to hit all three gears. It is possible to fail to shift - leaving you in neutral unless you quickly shift back to your original gear. Shifting is easiest when under power with a light load. Shifting the Dewalts was our major problem this year. At one point, we thought we had broken a tooth on one of the gears in the Dewalt, but after taking it apart, we couldn't find our what was wrong. Our best guess was that it wasn't shifting completely for some reason. RUSH quickly figured out that they were better off just keeping them in a single gear for the 2008 game.

We have made an alteration to the setup in the NBD paper. In NBD, the planet gears that mate with the gear on the drill motor are removed along with their supporting pins. Then the sun gear is reamed out to be fit onto a shaft. Instead of making this alteration, it is very possible to use the 4 pins that hold the planet gears to drive the sun gear by making a simple coupler. No machining of the Dewalt! This setup worked well for us the past two years and is especially useful when mating two motors to the Dewalt. (Any problems observed with our robots were from other sources.)

In the end, the difficulty in mounting the completed gearbox and the reduced efficiency as well as the costs required for additional hardware (belts, pulleys, bearings, etc.) have turned us away from the Dewalt for the near future.

Andy, the check will be sent soon.

-Mr. Van
Coach, Robodox
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