What is best for lowering the middle wheel?

I’m just wondering, what have other teams found to work best for lowering the middle wheel in relation to the other wheels in a 6WD system?

1/8" does it for us. It makes our robot rock back and forth about a degree. I can live with that. One thing we had a problem with last year though… when we welded our chassis, it curved upwards, so our middle wheel was more like 1/4" lower. When you’re welding your chassis (if its welded) make sure to evenly weld it, dont do one side and flip it over to do the other, or your frame will banana like our 2005 bot :stuck_out_tongue:

having a flexible frame helps keep all the tires on the ground somewhat.
so if you have a SOLID frame id go with 1/8 but bolted frames/more flexible frames id do 1/4

It really depends quite a bit on the type of tire treads you use. The softer and grippier (sp) your tires are, the more you need to lower the center wheel. We have found that with gum rubber Brecoflex belts, 1/8" was not enough.


A couple other things to consider is the amount your bot will sink into the carpet. Also the flex in the frame if it sags end to end. Last year I designed in a 1/4" but then got the bannana welding effect and it ended up being more like 1/2". Which actually turned out to be the magic number. I would say 1/4" is on the short side and a 1/2" max. Extra teeter is not a bad thing, but no teeter is a very bad thing.

I had this same question about our 6wd setup last year. I found that the offset distance varied, based on a couple factors. What tread you were using, how much “scrub” you wanted, how much “teeter” you could handle. In the end, it came down to the drivers feel for the robot. We used a series of 1/16" shims to fine tune the handling. We would go drive around until a battery died, then go back and add or remove a shim. When we found what worked best, we made a permanent shim and never touched it again.

Once it’s built, play around with a couple different shim heights. You’ll be amazed at the significant drivability changes, with such a small height different. Oh, and make sure this is done on a similar carpet to the playing field. Otherwise, all bets are off. :slight_smile:


Well according to the rules, you aren’t allowed to score from any position than your starting one. If they’re going to strictly enforce this, you are going to get penalties if you’re going to rock on your middle wheel. Good luck with getting away with that though.

EDIT: Starting position meaning vertically, not the position of the bot on the field.

can you post where you found this rule?

this would also cancel out turrets etc. seems wierd

I cannot understand what you’re trying to say.

If you’re saying that everything has to remain vertical–it does. Unless you do an absolutely terrible job of putting together your robot, and things are sliding up and down and back and forth, even if you rock maybe ~5* or something, everything on your robot still remains vertical with respect to the base of the robot. This is all that matters, as it would be illegal to climb the ramp if what you say is true.

And at any rate, I think you’ve entirely misinterpreted rule G17, as seen below.

<G17> ROBOT Orientation - ROBOTs must maintain their vertical orientation with respect to their starting
position throughout the match. ROBOTs may not intentionally tip over onto one of their initially vertical
sides and operate with this side parallel to the ground. If a ROBOT is accidentally or intentionally tipped
over onto its side, it cannot score any balls in any goals from this orientation.

It makes no mention of rocking back and forth, only falling over.

Oh. Thanks for clearing that up. I hadn’t read the rules in a while, but I remember that one, and I thought that you couldn’t shift from your initail vertical position at all, even if it was just a little.