pic: Team 100 Drivetrain In Progress

There’s really not enough here to bother calling this a teaser, so I won’t. Just a quick shot of our competition bot drivetrain last weekend…

We’re loving the VersaBlocks and Vex Pro belts in our drivetrain, and in a few other places as well. It’s a miracle how quickly a drivetrain goes together and how slick it looks with those guys.

Here’s to hoping this bad boy is shooting this weekend! T minus 13 days and counting…

So many CIMS! Looks good!

Slick. I like the black top rivets. Are you going to have to cut that middle shaft to fit it inside the frame perimeter?

I spy omni wheels…

Those CIMs are awfully close together.

Yep. We did it a few days after that picture was taken, just hack sawed the shafts off. And we’re huge fans of the black rivets too.

Yep. We like the ease of turning that they buy us, and their anti-defense qualities. It’s a ton easier to T-bone pin a robot with all traction than with omnis. We’d rather slide out of the way and keep driving than have us locked up by defense for 30 seconds.

True dat.

Have you actually tested this and found it to be true with your current wheel setup? I do not see how this would turn any better than a drop center with all traction wheels. Your traction wheelbase touching the ground is the same in both cases.

Also, I can see how the omni wheels will help you avoid T-bone situations if you are being contacted between the center traction wheels and the end of the robot with omni wheels, but you will be just as T-boneable from the section of your robot between the center wheel and the end of the side with traction wheels.

Why did you decide to include the middle wheel? Having just four wheels with one end omni and the other traction would let you turn better and make you almost impossible to T-bone.

-Mihir Iyer

It turns out that our drivetrain this year is actually really similar to our 2011 drive. That year, we had 6 4" AM performance wheels with roughtop, and found that even with drop center, the robot had a bit of difficulty turning on carpet. Even though the CG was firmly to the back off dropped center, the front wheels still scrubbed while turning. While experimenting before CalGames of that year, we found switching two wheels to omnis really improved turning performance, as they reduced the amount of lateral friction even in wheels which were nominally not contacting the ground. We turned a ton better with 4 traction 2 omni than we did with 6 traction.

One dirty secret about 6wds is that despite the drop center, all 6 wheels still contact the ground, just to varying degrees. Depending on your total mass, wheel type, and center of gravity, you’ll just put different amounts of force on each wheel, and engage the carpet at that wheel more or less. Unless you have some totally crazy center drop, your other wheels will still contact the carpet to some degree. The center drop just keeps you from really digging in the farthest out wheels at the same time, which would percent you from turning.

In any case, the WCD VersaChassis makes it super easy to switch out wheels. We can literally switch between any combination of omnis/versa wheel/versa wheel DT/rough top in about ten minutes. If we figure out that we don’t like the omnis, we won’t use them. We could also go all omnis is we wanted to. The setup seen in that photo is our best guess for the best wheel configuration for this game, given our teams past experiences, and from observing other teams drivetrains. I think we’ll play around with the wheel configuration after seeing how the robot handles on carpet and interacts with defense.

Hopefully I’ve answered your questions to satisfaction. I love talking about this stuff, so if you’d like to hear more, I’d be more than happy to oblige.