pic: Did Somebody Say Defense Game?

[JohnFogarty]

This makes me glad we chose 6CIM drive.

[cbale2000]

Originally Posted by Chris is me

I don't see this as having much higher turning scrub than a six wheel drive. In theory, this system would behave like a tread drive and this would turn even without drop. I guess we shall see!

Our wheels are set at a 32 foot arc, which allows the drive to act, more or less, like a 6 or 8 wheel drive at any given time. What we've found over the years, however, is that during a pushing match with a typical 6WD robot, the forces of the two robots can actually push 6WD robots onto their back set of wheels and lift their front and middle ones up (even just a little), thus reducing their traction and making them effectively 2WD robots. Having extra wheels on an arc helps ensure constant contact with the floor during all conditions.

Originally Posted by Garrett.d.w

...If I were holding the joysticks in this case :

That pretty much sums up what I'm expecting.

Originally Posted by Duncan Macdonald

Is this a similar design to what your team ran in 2008? If so, what reliability changes were made?
2008 robot
Context (Still one of the classiest decisions in FIRST history)

2008 was an interesting case, we had a situation where we had a custom gearbox, that had a 3rd stage consisting of an 8 tooth gear that undercut a 50+ tooth cast iron gear, which was custom made (with a 3 week lead time to get more) and we had forgotten spares (and we were in Canada). This years robot, by comparison, uses standard VEXPro 3 CIM Ball Shifters, with parts we can get easily, and if necessary pick up from The Robot Space (one of the new VEXPro partners), less than an hour away.

The drive system itself is also much closer to our 2007 bot due to the use of gears to drive the wheels, rather than chain, and a very similar gearbox configuration to the drive we had that year. With the exception of a bearing failure in the finals of West Michigan (which we went on to win anyways), there was virtually no reliability issues with the 2007 drive system.

Originally Posted by Animal Control

Yes. Can you sent a video with it running

Soon, I'm hoping we have it driving next week.

Originally Posted by magnets

Adding surface area in contact with the ground (up to a point) increases traction. It doesn't matter if it's through wider wheels, or more wheels. If friction worked just the way the coefficient of friction says it will, then neither width nor number of wheels will affect traction at all. You could have three 0.1" thick wheels, and have the same amount traction, but friction doesn't follow the super simple columbic prediction, especially on carpet.

Exactly, our wheels this year are also wider than we've used before (1.5in wide this year, compared to 1in past years), so we're hoping they will provide us with a bit more traction.

Originally Posted by wilsonmw04

How long are you going to have in a pushing match with a 6 cim drive before you start popping breakers?

We had no issues with the individual 40A breakers on our 2007 robot (the predecessor to this design), now, whether or not the 2 additional MiniCIMs cause the main breaker to pop is another question. We're using such a low low-gear that we should loose traction before stalling the motors though (at least, this has been the case on past machines).


Apologies for the wall of text, just figured I'd answer all the questions in one go.

[Christopher149]

Their 2007 'bot for reference.

[BBray_T1296]

Originally Posted by wilsonmw04

How long are you going to have in a pushing match with a 6 cim drive before you start popping breakers?

well, you should be fine operating at 39amps per motor for a while
And if you are worried about the 234 amps on the main breaker, allow me to show you the current graph as per the manufacturer



As you can see, you can draw 200% (240 amps) for 10 seconds minimum, as per the specifications

EDIT: link fixed?

[wilsonmw04]

Originally Posted by BBray_T1296

well, you should be fine operating at 39amps per motor for a while
And if you are worried about the 234 amps on the main breaker, allow me to show you the current graph as per the manufacturer



As you can see, you can draw 200% (240 amps) for 10 seconds minimum, as per the specifications

link is broken, please try again. I'm worried about the snap fuses. I've seen what a resetting snap fuse does to a robots drive train. It isn't pretty.

[nathannfm]

Any reason you chose to assemble the 2 gearboxes identically instead of mirror images (which would have made the drive symmetrical)?

[BBray_T1296]

Originally Posted by wilsonmw04

link is broken, please try again. I'm worried about the snap fuses. I've seen what a resetting snap fuse does to a robots drive train. It isn't pretty.

Really? I can see it just fine.
Anyways, that pic is a screenshot from this pdf, page 34 you will find our switch.

So long as you do stay within the 40amps per motor, you should not need to worry too much about the main