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Unread 30-04-2008, 10:23
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How much torque can the Dewalt Trannies take?

Has anyone driven the stock dewalt transmission components to failure, and if so, what did it take?

We're planning an offseason project that will interface three cims into the input of a single Dewalt. I know 2 cims has been done through a single Dewalt, but I think I'm probably riding the hairy edge of failure adding the third.

Anyone with some info on what I should expect to fail first? Standard input per the NBD whitepaper.
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Unread 30-04-2008, 10:24
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Re: How much torque can the Dewalt Trannies take?

You should check out the robonauts drivetrain from last year. I believe they routed 4 CIMs and 2 FPs through 1 dewalt.
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Unread 30-04-2008, 11:22
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Re: How much torque can the Dewalt Trannies take?

Quote:
Originally Posted by Brandon Holley View Post
You should check out the robonauts drivetrain from last year. I believe they routed 4 CIMs and 2 FPs through 1 dewalt.
They did have back-ups, including a multi-DeWalt version. I do not believe they had to use them though.
Others teams have managed to "liquify" (their words) the insides of a DeWalt with many fewer motors running through them.
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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, 12:37
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Re: How much torque can the Dewalt Trannies take?

1323 wants to use the dewalts. Can anyone shed some light on the pros and cons and how fast they went with one cim. Thanks
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Unread 30-04-2008, 16:18
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Re: How much torque can the Dewalt Trannies take?

To the best of my knowledge Rush was twisting their driveshafts, not their trannies, but I could be wrong! Hope he can add some input as well. Rush was one of the faster heavy teams out there this year.

It was very educational watching battery voltages throughout the matches on the IFI screens - for instance during the 4 minute practice matches chicken's voltage was running down in the 6's and 7's, but they may have been using old batteries. Many other teams were dropping down that low as well at the end of 4 minutes. This year was a hard one on batteries - but that's for another topic.

RC - before someone beats you over the head with it, I suggest you do some searches on the forum. There's a white paper on dewalts to get the ratios and then it's a very easy excercise to use JVN's design calculator to figure out how fast you'll be moving.
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Unread 30-04-2008, 16:25
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Re: How much torque can the Dewalt Trannies take?

I also believe that Rush was breaking drive shafts. I don't believe that the dewalt themselves were giving them trouble. Another great thing about the dewalt is that it is so cheap it is easy to have spares, but I think that the transmission itself is very strong. We are going to try 2 cims into 1 dewalt driving high traction treaded wheels this summer and report back on any problems.
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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
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Unread 30-04-2008, 17:25
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Re: How much torque can the Dewalt Trannies take?

Can you post some pics of the two cim dewalt gearbox?
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Unread 30-04-2008, 18:14
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Re: How much torque can the Dewalt Trannies take?

I would like to see pictures of the transmission as well. Pictures of Rush's would be great too.
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Unread 30-04-2008, 22:57
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Re: How much torque can the Dewalt Trannies take?

OOO *rubs hands together* my favorite subject!!!
Dewalts can hande A TON of abuse, they are designed to be used in 12 v cordless drills, used by professionals and craftsmen world wide, designed to take abuses and stress beyond the capabilities of one robot.
Team 418 has been using dewalt transmissions for 4 years now, and never had the transmission itself fail. we initially followed the NBD paper to the letter, but recently have taken to doing some things of our own including:
- change from reaming the carrier to machining a plate to fit on the planetary pins
- the carrier plate allows us to save time by not having to sand down the gearbox housing to a certain depth, just trim the CIM shaft down!

These things are bulletproof as long as they are thoughtfully put together (use the right screws, lock tight etc.) and we an recommend them to any other team looking for a cheap and easy multi speed transmission.

2 speed shifting is smooth, but 3 speeds gets a little tricky... but we have never actually seen a need for the 3rd speed (12:1, 4:1, 3:1 not much difference)

mounting them could not be much easier, a securely tightened shaft collar clamped around the gearbox holds the entire assembly very well.

118's V6 with the dewalt was a very powerful and innovative system that took full advantage of the compact and strong multi speed transmission that the dewalt offered. im not sure what part of their drive train broke during LSR finals that year though, rumor has it that it was the V6 though. Pavan, care to fill us in?

as a last testament to the robustness of the dewalt, our team has used the same model dewalt drills for about 5-6 years now and never had anything go bad besides the battery, and these things are still working great!
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Unread 30-04-2008, 23:08
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Re: How much torque can the Dewalt Trannies take?

Heres a question. If money did not matter as well as time, would you go with a Dewalt gearbox or a Andymark gearbox? Is there anything that would make the Dewalt better then say a Andymark supershifter?
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Unread 30-04-2008, 23:10
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Re: How much torque can the Dewalt Trannies take?

Quote:
Originally Posted by Lowfategg View Post
Heres a question. If money did not matter as well as time, would you go with a Dewalt gearbox or a Andymark gearbox? Is there anything that would make the Dewalt better then say a Andymark supershifter?
Depends on the application. 3-speed or 2? 3-speed, Dewalt. 2-speed, AndyMark.

I'd go with AndyMark if I was in a time crunch. Very little assembly, if any.
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