pic: Drivetrain Prototype

Hey Art,

You might be interested in the discussion going on here:

(mixing Victor and Jag controllers for 2 CIMs on one toughbox)


There are also another, less obvious benefit of having your CIMs in your drive. It will help keep your CG lower. 10lbs of CIM motors is a pretty decent amount of weight that you want to keep as low as possible.

Op, my only suggestion to you is to use the Toughboxes in the KOP. Not knocking the P80s at all but why spend money when you don’t have to? Also, a word of caution, a wide stance bot like this will be susceptible to tipping if your CG is too high. In a game where you have to have a large arm lifting a heavy object (2008, 2005) I would be cautious about using a wide stance bot like this without outriggers (see 118 in 2005 or 33 in 2008 for a good example).

On the “wide stance tipping” comment I’ll back that up, all the way up until the point where the arm is required to reach right to left of the robot. Then wide stance would probably be the better option. (In my opinion)

I’ll echo what Akash said. If you aren’t going to flange the metal, don’t put holes in it. You need that strength. (If you don’t know what flanges are, I’ll be more than happy to explain.

Also, your bars going all the way across. You really only need them to be 1/8" wall. I would put three on top, two one bottom. Or even two on two, and two on bottom. I would also only take them across the center of the chassis and then use stand-offs to support the outer cover, done right you will be plenty strong enough.

My $0.02

Looks good, but here’s a suggestion: Your front-to-back wheelbase dimension looks pretty short. Looks to be quite unstable in terms of tipping forward or backward. For any wide format chassis, this is always an issue, and the wheel centers usually need to be pushed as far apart as the frame design allows. Most FRC games require the robot CG to be high enough that tipping can be a problem if the wheelbase gets too short. Perhaps you are trying to shorten this distance to enhance turning. That is a factor, but is usually not as important as staying upright.

Now that I think about it, you’re right. this years robot had many issues with 35 chain, but the 25 chain never failed.

but still, if you take the time to tension the sprockets properly, timing belt is another option

There is no question that 35 chain is more forgiving than 25. It allows for much more carelessness in design and misalignment albeit at a huge weight penalty. I would look at the systems in question on your design and try to identify the cause of the failure as it is not from the chain itself but rather the implementation.

Using a drivetrain with less than 4 CIMs in FRC is something that should be approached carefully (I’m trying to get as close to saying “never” as possible without saying it). If you don’t shift, I would only use it in the extremely rare case that your drivetrain is only used for a short while in a match, like 125’s robot this year which cannot function on the ground basically. Traction limited driving with 1 CIM is a painfully slow speed, acceleration will take a hit, and you basically just lag behind. Using KOP wheels to lower traction in order to rectify this makes you lose in pushing. Adding a shifter can help then, but you’re still getting up to 7-8fps rather slowly and with a high current draw. 4 motors can give you a nice 6.5 fps or so with a good balance of current draw, acceleration, and traction-limited-ness. Your drivetrain is the absolute most important mechanical system on the robot. Before you shortchange it, make sure you fully understand the tradeoffs and do the math.

My team has used drivetrains that use only two CIMs for as long as I can remember (exception 2004 when we used four gearboxes) and we know that being torque limited is a major problem. In general our only problem was overheating. In the past we dealt with this by making heatsinks for the CIMs so as to prevent them from over heating. In my opinion how you choose to distribute you CIMs really dependes on the challenge.

I blame frame warping. Boston was no issue for the drive-train, Atlanta was a totally different story. But the complexity of the chain runs probably helped
(double sprocket on tough-box to double sprocket on bearing blocks to wheel to wheel [times 2]) + (double sprocket on tough-box to wheel to wheel [times 2])
{we had a double sided drive-train and needed to get power to both sides.}