Chief Delphi

Chief Delphi (http://www.chiefdelphi.com/forums/index.php)
-   Motors (http://www.chiefdelphi.com/forums/forumdisplay.php?f=52)
-   -   How much torque can the Dewalt Trannies take? (http://www.chiefdelphi.com/forums/showthread.php?t=67388)

Lowfategg 30-04-2008 23:15

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by EricH (Post 744646)
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.

Lets say we were only looking at the Dewalt as a two speed since the person before me said its hard to get 3rd gear to work.

Lil' Lavery 30-04-2008 23:47

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by Lowfategg (Post 744648)
Lets say we were only looking at the Dewalt as a two speed since the person before me said its hard to get 3rd gear to work.

DeWalts are a planetary transmission, and as a result have all the advantages and disadvantages of it. The biggest advantage is the much smaller size of the transmission. This is especially important in less than "traditional" drive designs where transmissions might not have as much space. Non-coaxial swerve systems often are forced to have the motors and any reductions (transmissions) rotate with the swerve modules. If a team were to opt for a multi-speed, non-coaxial swerve system, DeWalts would definitely be the way to go. Of course there's plenty of other scenarios where DeWalts would be advantageous for their size as well, that's just one extreme case.

Lowfategg 01-05-2008 01:01

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by Lil' Lavery (Post 744656)
DeWalts are a planetary transmission, and as a result have all the advantages and disadvantages of it. The biggest advantage is the much smaller size of the transmission. This is especially important in less than "traditional" drive designs where transmissions might not have as much space. Non-coaxial swerve systems often are forced to have the motors and any reductions (transmissions) rotate with the swerve modules. If a team were to opt for a multi-speed, non-coaxial swerve system, DeWalts would definitely be the way to go. Of course there's plenty of other scenarios where DeWalts would be advantageous for their size as well, that's just one extreme case.

Being that I am new to FRC being from FTC I don't really know the advantages and disadvantages of a planetary transmission (since my FRC team did not play with them). From what I can see I love the idea of them and they seem like they would be very good. But from what your saying the Dewalts are good because of there size.

Lil' Lavery 01-05-2008 01:26

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by Lowfategg (Post 744668)
Being that I am new to FRC being from FTC I don't really know the advantages and disadvantages of a planetary transmission (since my FRC team did not play with them). From what I can see I love the idea of them and they seem like they would be very good. But from what your saying the Dewalts are good because of there size.

In short, planetary gearboxes are a much more compact method of getting reductions than standard spur gears, but are far less efficient.
For instance compare the banebots transmission to the AndyMark toughboxes.
http://banebots.com/pc/P80A-nnnn-000...80A-43-0005-R2
http://andymark.biz/am-0145.html
While the banebot's transmissions had other issues in reliability that caused them to be unpopular, the differences in dimensions for gearboxes with essentially the same reduction are apparent. This is magnified even further when comparing a shifting transmission such as the AndyMarks to a DeWalt.
http://en.wikipedia.org/wiki/Spur_gear#Spur_gears
http://en.wikipedia.org/wiki/Planetary_transmission

Lowfategg 01-05-2008 01:47

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by Lil' Lavery (Post 744671)
In short, planetary gearboxes are a much more compact method of getting reductions than standard spur gears, but are far less efficient.

Ok thank you. Thats what I thought when I looked at planetary gearboxes.

Nikhil Bajaj 01-05-2008 01:56

Re: How much torque can the Dewalt Trannies take?
 
To the teams that usually use these transmissions, do you typically use servos or pneumatics to shift? I can see advantages/disadvantages to both...

MrHance 01-05-2008 03:54

Re: How much torque can the Dewalt Trannies take?
 
Haven read the thread up until now, and being one of the mentors from team # 647 that wrote the white pape for NBD. It is in my opion that the Dewalts are the way to go for many reasons. Just a few: 1) compact, 2) durable, 3) versital, 4) No need for pnumatics and if I took the time to think up a few more from Afghanistan, I'd put them in. The drawback is that they consume battery power because you use some many motors. The shifting issue can be addressed with proper program for the shifting of the tansmission. For the most part we use the shifting only on the drive system. When we use them for other applications, we selected the gear ration that we need and left them there. No Problems. You have to be very precise on you application and setup when using the Dewalts with any motor combination. Do not be afraid to experiment with them. Only your team can decide the best way to apply them in every setup that you do. Not everyone will come up with the same solution. Have a Nice Day!:)

IKE 01-05-2008 08:44

Re: How much torque can the Dewalt Trannies take?
 
This is a good problem to do the math on. When you go with a lower overall ratio and therefore more speed, the back drive torque into the transmission actually goes up. Where this applies to this year's game is that the ratios that people were using to get the really high speeds allow for more backdrive torque into the transmissions. We had a dual CIM Single Dewalt design that we were intending to use. This design had a reduction before the Dewalt as part of the 2to1 interface. We decided against it when we ran the stress calcs on the output shaft of the Dewalt. With the speeds we wanted the stress on that component would require a pretty exotic material (approximately 200ksi). While I am sure they are using an extremely strong alloy for that shaft, the factor of safety was just too low (1.2 top depending on exact alloy). One thing for teams to remember is that sometimes the forces coming back into the driveline (especially when a defender hits you at 10 fps) can be way higher than the forces going out. Again this was for our specific design. We ended up going with the old school AM shifter and with some small modifications. They were bullet proof in this design.

If there is a big request for it I will dig those calculations up and put together a paper otherwise I recommend that people run the exercise for themselves.

All that being said, I think the Dewalts are an excellent choice for typical FIRST games. We used them in 05, 06, 07, and 08 in various applications. We have had problems, but that was due to us thinking that we knew better than the NBD paper. Should you use DeWalt's follow that paper to a T and respect every detail. The biggest problem we had is that when we didn't follow the paper, we didn't get immediate failures, we got the kind that only show up after say 8 or 9 hard matches. This leads to a very stressful Saturday.:mad:

R.C. 02-05-2008 11:25

Re: How much torque can the Dewalt Trannies take?
 
I would love to see those calculations, thanks

Tristan Lall 02-05-2008 12:47

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by IKE (Post 744709)
This design had a reduction before the Dewalt as part of the 2to1 interface. We decided against it when we ran the stress calcs on the output shaft of the Dewalt. With the speeds we wanted the stress on that component would require a pretty exotic material (approximately 200ksi). While I am sure they are using an extremely strong alloy for that shaft, the factor of safety was just too low (1.2 top depending on exact alloy). One thing for teams to remember is that sometimes the forces coming back into the driveline (especially when a defender hits you at 10 fps) can be way higher than the forces going out. Again this was for our specific design.

In 2006, 188 had some similar issues with custom DeWalt outputs. Basically, we were breaking the output shaft after several matches worth of hard running. Although solidly mounted, the steel shafts we substituted for the stock ones were not heat-treated, and failed in torsion.

We actually used a different strategy to mount the whole thing. We eliminated all of the DeWalt plastic housing, removed the clutch selector and its stop, and removed the cosmetic cover on the shifter. Then we made a new adapter for the planet carrier out of acetal, with holes to match the pins on the planet carrier (instead of removing the pins). A turned plywood plug capped off the back of the transmission, and set the clearances for the planetary stage. We then tapped the existing holes on the cast aluminum housing for #6-32 UNC threaded rod, and used four tie rods to pull the entire assembly tight against an aluminum plate (part of a 2:1 gearbox with a pair of CIM motors attached, and options for other kit motors as well). We also removed much of the grease from the DeWalts, in a bid to boost efficiency somewhat (when you're looking at something like 70%, you do what you can...).

Apart from the output shaft issue (which would likely have been solved if we'd substituted hardened steel), and some manufacturing errors in the CIM gearbox, the design seemed solid. The DeWalts themselves showed no signs of wear. On the other hand, there was never any need for the top gear (in our configuration); it was set for around 16/12/4 ft/s (if I remember correctly), and truth be told, with that particular robot and without very careful deceleration, use of top gear would land the robot on its back. Servo-actuated shifting was sluggish compared to the pneumatic dog shifting on Woburn's 2004 two-speed, but because that robot spent most of its time in low gear, it didn't become an issue. We shifted it under full power in testing, without any problems.

sdcantrell56 02-05-2008 13:30

Re: How much torque can the Dewalt Trannies take?
 
Could you post up pictures of that transmission (188). That post is very informative and it is starting to confirm my belief that if at all possible we should try to use a custom dog shifting transmission, especially if cost is relatively close (within $100 per transmission).

ajlapp 02-05-2008 20:13

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. :)

fimmel 02-05-2008 21:06

Re: How much torque can the Dewalt Trannies take?
 
team 885 had a few issues with them this year, it was simply error, TAKE THE BACKDRIVE PINS OUT if your going to use it in a drive train. they managed to grind the insides on thursday. (this is what i have heard from some of their mentors)


...forest

roboticWanderor 02-05-2008 23:25

Re: How much torque can the Dewalt Trannies take?
 
Quote:

Originally Posted by ajlapp (Post 745270)
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.

WOW that is a lot of work there guys! great job, cant say i haven't fantasized about the dual cim dewalt transmissions a few times myself. i have probably mentioned this before, but the carrier adapter plate provides a much much better solution compared to EDMing that stage. Like you said, i would also recommend putting the further gear reduction After the dewalt to make sure you don't run into those torque problems anymore.

Aren_Hill 03-05-2008 00:23

Re: How much torque can the Dewalt Trannies take?
 
i can attest after last years bot with 1 cim dewalts are practically bulletproof if you follow every part of the NBD whitepaper.

And this year we a fp motor run through one to pull back our shooter, and the antibackdrive pins really came in handy, that setup was installed once and left, our shooter never broke.


All times are GMT -5. The time now is 07:40.

Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi