pic: FRC 4532 Drive Base Frame



Here’s our 2012 robot drivetrain! 4 Wheel Drive, with plenty of clearance for the barrier!

I predict a lot of difficultly turning. Make sure you load that up to 140-150lbs and try driving and turning on carpet before you run out of time to make changes.

This +[all of it].

How big are those wheels?

The wheels are 8" AndyMark Pneumatic ones!

We did all the math! It might be a little slow turning, but at 150lbs it should turn fine!

You really should do what the others have suggested. Load it up and try it. The MATH is not going to predict what the turning will be like. Experience has shown MANY teams that turning a 4 wheel long chassis bot is like trying to ride a wild horse. They tend to jump around a LOT especially with grippy tires.
Bruce

This word is what will bite you in the butt.

It is imperative that you test this drive base at full weight and get some 8" omni wheels on order as a contingency.

Math is all well and good, but make sure you load some weights from a weight room on that to bring it up to full weight and actually drive it around. Reality is what you’re interested in, and it’ll give you and your drivers a good idea of what you’re gonna be dealing with.

What a beautifully elegant drivetrain. Gotta love the simplicity of dropping the unnecessary extra 2 or 4 wheels that most teams typically use. Plus this robot is going to do quite the sexy shimmy everytime it turns. Could you ask for anymore?

You’re on a great path…keep it up!

I’m going to echo all the posts above, and share our horror story. We built something very similar many years ago. We tested it on tile and smooth concrete surfaces, and it turned like a dream. We didn’t have any carpet, and didn’t think it would matter much. When we got to our first regional and took it out on to the field for practice, it skipped, shook, shimmied and bounced every time we tried to move. We couldn’t control it at all. We had to pull two wheels off and replaced them with castors to even get some control. It wasn’t pretty.

If you want to go with those 4 wheels, don’t go with a long configuration, go wide. It will work a whole lot better. Otherwise, look at putting omnis on instead.

Welcome to FIRST and welcome to CD!

Good luck!

Steve

I’m telling you, this drivetrain is money! We’re using AM Toughboxes with an external sprocket reduction of somekind, (I don’t know, I’m a software guy!) to give us a final speed of 6.2xx fps. Should be enough torque to overcome the carpet scrub, right? We don’t need to be fast this year, absolute precision is key!

The toque not the problem. The front wheels will try to grab the carpet as you turn resulting in a very jerky motion. I built a float like thing for school and the thing could only move forward and back because the wheels simply would not turn with a small person on it.

And I’m (we’re) telling you, a ten year veteran of FRC mechanical systems, that this 4WD drivetrain might have some serious issues and that you need to test it out before you assume that it will work. We are all trying to help you out here.

The jumping, jittering, unstable turning is VERY characteristic of this sort of drive train; and, as SteveGPage said, it is NOT precise at all, but instead is nearly un-drivable.

I agree! It looks like you’ve opted against the AM Kit base and have instead gone with sheet metal frame construction? If so, it looks very simple, elegant, and robust!

As others have said above though, you may have trouble turning because of the amount of “Scrub” that a 4wd in long configuration will produce. You could either add 2 center wheels (dropped 1/8" lower than the outside wheels) to shorten the wheel base, or you could change out the front or back 2 wheels for non-traction wheels like Omnis or Slippery wheels.

I’ll be keeping my eye on 4532 for some updates over the rest of the build season. Looks like an impressive rookie already! What regional(s) will you be attending?

Thanks for your positive comments!

Yes, we have a very generous sheet metal shop down the road from us, and we’re near a Bosch tubing distributor as well! Our frame is basically free this year!

Are you trolling and actually going to use 8-inch “Mechanums”?

I assume this by your username.

-Clinton-

Unfortunately, my team outvoted me on this. There is a catch to being a software guy!

I was wondering the same thing, this would actually make sense.

On the other hand, your frame looks nice and solid.

Does it drive yet? If so, weight it up and turn it on carpet (and videotape it). If it doesn’t, your main concern should be getting it there. It looks easy enough to switch in omnis if you decide you need them. Either way, I’d suggest you stop extolling the hypothetical performance without recording the actual one. That’s plenty to do itself, good luck!

I have to say, congrats to you as a rookie team for being able to design your own drive base. It’s also good to see how enthusiastic about it. It’s definitely an achievement!

However, I do need to echo some of the sentiments posted here. You really need to test this drive configuration on carpet, and never assume it’s going to work perfectly. On my team’s rookie year, we did not have carpet to test our drivetrain on that was identical to the field’s. We got to competition, and we found, after several matches of frustration, that our drivetrain was not outputting enough torque to move on the carpet, and we were tripping our breaker. Our second year robot had a 4 wheel drivetrain, and while I don’t remember it being impossible to steer, I do remember it having a bit of trouble trying to turn under high speed.

So just as others have suggested, really try to test this in real world conditions, and don’t assume anything. Believe me, 20 minutes of testing now can save you a day of frustration and frantic work during competition.