Using two CIMs in the Banebots Transmission

[JamesBrown]

Originally Posted by MikeJ675

My thoughts on that was that for not much extra cost(about $90), you can get much greater reliability by just getting two more gearboxes.

With a relatively untested gearbox, I'd be hesitant to put two cim's through a single one. Two separate gear boxes per side will reduce the strain on the gears in each gearbox and provide at least some power on each side even if a gearbox fails.

Any weight difference between the adapter weight and the gearboxes could probably be made up with less chain use.

While the gear box is untested in FIRST is is my understanding that they are quite popular in battle bots and other competitions.

Our team however invested in some AM 2 speeds and I think we will be using them again.

[Greg Perkins]

Originally Posted by JamesBrown

While the gear box is untested in FIRST is is my understanding that they are quite popular in battle bots and other competitions.

Our team however invested in some AM 2 speeds and I think we will be using them again.

They are used in Battlebots, in the 12 and 30lb competitions locally. The Banebots gearboxes have performed phenominally in battlebots, but I'd be hesitant to put that much through an essentially over-engineered drill transmission. Buy 2 more and run 2 on each side, factor of saftey will be good.

[sanddrag]

Okay, so say you've got 5" wheels perfect size to direct drive. 6 of them, 3 per side. What do you do? Buy the double motor kit, direct drive the centers with a single planetary and run chains out to the corners is the most logical thing. But only if "it'll hold." I mean, 4 planetaries with 6 wheels? It's not clean. So, will they hold up with two CIMs in there? Joe Johnson have any input?

[Justin M.]

Hmmm...after some thought I think I just might get two more gearboxes, with a total of 4. The robot design would be for 4WD, so now that I think it would make more sense to have each wheel be powered by it's own independent gearbox/chain geardown. It'll wind up costing us almost double, but worth it. Double the strength and reliability, with the same current requirements as a doubled gearbox.

Back to Autodesk....

[lynca]

The kit sprockets (28 tooth and 16 tooth), give a reduction of 1.75:1 , in addition to the 12:1 , which is around 21:1 ,

5280 no load rpm ---> 251 rpm with the reduction ,. this still seems kind of fast with the standard kit size wheels, are you using other sprockets not provided in the kit ?

[dtengineering]

Originally Posted by lynca

The kit sprockets (28 tooth and 16 tooth), give a reduction of 1.75:1 , in addition to the 12:1 , which is around 21:1 ,

5280 no load rpm ---> 251 rpm with the reduction ,. this still seems kind of fast with the standard kit size wheels, are you using other sprockets not provided in the kit ?

251 rpm is 4.2 revs per second. With a 6" dia. wheel the circumference is 18.8 inches, giving a theoretical top speed of 6.6 feet per second. (Or 2m/s aka 7.2km/h) With smaller wheels, you'll be slower.

Depending on your team's strategy you might like the pushing power that offers or you might want to move faster. I'm looking at the opportunity for direct drive from the tranny output shaft and a bit more speed.

Someone earlier posted about how best to drive a 6wd chassis with four gearboxes. I'd say direct drive to two axles and chains or belts linking all three axles.

Jason

[Justin M.]

As of now the gearboxes will be run on each independent chain geardown, on each wheel. I haven't decided what size sprockets to run yet; this is going to be one of those things we'll swap out later in testing. I assume I'll start with the stock sizes given in the KOP, then adjust accordingly. Right now our main concern is getting the bot modeled in CAD with the 4 gearboxes so we can get to work on our chassis....sprocket sizes and geardown can be adjusted later, we have tons of extra sprockets lying around.

[Joe Johnson]

Originally Posted by Justin M.

Hmmm...after some thought I think I just might get two more gearboxes, with a total of 4. The robot design would be for 4WD, so now that I think it would make more sense to have each wheel be powered by it's own independent gearbox/chain geardown. It'll wind up costing us almost double, but worth it. Double the strength and reliability, with the same current requirements as a doubled gearbox.

Back to Autodesk....

This is an age old design choice. In general, I come down on the chain between the wheels camp rather than independently driving each wheel. It boils down to this: When you are pushing against another robot, your front wheels tend to lift and your back wheels tend to get more weight on them. This means that your front wheels are likely slipping and your back wheels are doing most of the pushing. In the independently driven wheels case, only your back motors are doing any useful pushing. This is not why you wanted 4 motor drive! So... whether you buy 2 planetary gearboxes or buy the adaptor to drive 1 planetary gearbox with 2 CIMs, I highly recommend that you consider having chain link all your wheels (and by the way the right number of drive wheels is 6 -- FYI).

Joe J.

P.S. It is my considered opinion that the Banebot 56mm gearbox is sufficiently over designed for 1 CIM motor that it can easily accept the load of 2 CIMs. In fact, I think it be converted to accept 2 CIMs AND a Fisher Price in case you are in the Team 25 Camp (a.k.a. The 3-Motors-Per-Side-Minimum Camp)

[Justin M.]

Originally Posted by Joe Johnson

This is an age old design choice. In general, I come down on the chain between the wheels camp rather than independently driving each wheel. It boils down to this: When you are pushing against another robot, your front wheels tend to lift and your back wheels tend to get more weight on them. This means that your front wheels are likely slipping and your back wheels are doing most of the pushing. In the independently driven wheels case, only your back motors are doing any useful pushing. This is not why you wanted 4 motor drive! So... whether you buy 2 planetary gearboxes or buy the adaptor to drive 1 planetary gearbox with 2 CIMs, I highly recommend that you consider having chain link all your wheels (and by the way the right number of drive wheels is 6 -- FYI).

Joe J.

P.S. It is my considered opinion that the Banebot 56mm gearbox is sufficiently over designed for 1 CIM motor that it can easily accept the load of 2 CIMs. In fact, I think it be converted to accept 2 CIMs AND a Fisher Price in case you are in the Team 25 Camp (a.k.a. The 3-Motors-Per-Side-Minimum Camp)

Thanks for the tip. I was considering doing that to distrubute pushing power among all the wheels. Just run a chain from the output shaft to the wheels, then attach an additional sprocket to the opposite side of the wheel, and run a chain connecting the two wheels together with the same size sprockets.

[Billfred]

Originally Posted by Justin M.

Can you attach two sprockets to the AndyMark wheels in the kit?

I haven't tried it with these exact wheels, but last year 1293 ran two sprockets off of an IFI wheel in their 6WD setup. You've got to put a little space between the two sprockets through your choice of method (either bolt them on both sides or put a spacer on the bolt holding them on), but it's entirely possible.

[Justin M.]

Originally Posted by Billfred

I haven't tried it with these exact wheels, but last year 1293 ran two sprockets off of an IFI wheel in their 6WD setup. You've got to put a little space between the two sprockets through your choice of method (either bolt them on both sides or put a spacer on the bolt holding them on), but it's entirely possible.

I answered my own question shortly after typing it...

The AndyMark wheels have holes in a circular face pattern for a sprocket. You have to tap the threads into the hub yourself, which makes it 100% possible, you just need to use >.5" long bolts on each side for a tight fitting of the sprockets.

[zander_108]

Originally Posted by Tri_Lam

uhhh what are cim's ~_~

cims are the 2 suplied black motors that the kit comes, but there is a difference between them and the even larger "mini-bike" motor that has the belt pully and tensioners on it.

[Tri_Lam]

thx heh i just called them black motors

[zander_108]

ha, its ok, dont sweat it