Wheel size considerations

What are teams thinking of in terms of wheel size and style? Larger (e.g. 12 inch) wheels have a shorter wheel base due to the need to have their centers closer together, but allow for lower kicking mechanisms while still having enough clearance to go over the bump-- specifically due to the smaller wheel base.

If you want a lower kicking mechanism with a smaller wheel, you can use brackets like those in the KoP to mount your wheels lower than your frame. Though a shorter wheelbase isn’t always a bad thing.

Generally the larger the weels, the higher the Center of Gravity. So if you get more clearance for the bump, you also increase the odds your robot will fall over on the bump.

It’s an interesting conundrum.

Larger wheels in a 4WD configuration do help with ramp climbing, specifically due to their increased ground clearance, but they may also cause issues with your COG because they’re raising your drivetrain up so much.

Personally, We’re leading towards using 6" wheels in an 8WD because it allows us to build a much lower base in addition to having excellent maneuverability. Also, due to the wheel placement and geometry of the frame, the 8WD should have no problems with climbing the bump.

I’d Imagine with proper wheel configuration one could use as small as 4" wheels and still be able to climb the ramp successfully.

I think there are a few prevailing drivetrain ideas, one being a four wheel where one wheel “falls” over the bump, then the high frame prevents the robot from high centering before the second wheel negotiates the ramp, and the more than four wheel approach that lowers the CoG in exchange for putting more of the robot in the air at any one time. I’m suspecting this debate will rage on into the competition season; is the decreased turning (or decreased traction) worth the increased stability of high 4 wheel drive?

I expect the bumps were designed so that they all work out pretty much the same…and we’ll see all kinds of neat robots as a result!

For what its worth we have designed an 8wd frame using 5" wheels with no chance of bottoming out. Getting creative with the frame helps a lot

My team is discussing 4WD… 8" wheels and with the 29" wheelbase that we want, I just went through the calculations, and our robot will make a MAX 24.443 degree angle with the playing surface…
that is ALOT less that I had originally thought!

I dont think huge wheels would make any better improvement on this…

so what you are saying is you can do this within 1 / 1000 of an inch ?

Yeah, that’s where we’re leaning to.

What do you mean, exactly…?:confused:

We, team 1261, have a couple of ideas in the mills. They are both 10WD, but not all 10 wheels can necessarily touch the ground at the same time. They are primarily to insure that we clear the bump.

Although now that I think about it…one of the 10WD designs has a potentially crippling flaw…

do what? climb the ramp?
no, I do not plan on designing that little tolerance…
this is just a theoretical angle based on exact numbers.

there are too many variables to call it that close. As it stands right now, our bot has about 1 and 1/2 inches of clearance over the top of the bump…

sorry about that… I was just being a wise guy.

If you specify something to to that many decimals that implies your working precision. When you go to college and start your lab work you have to learn to be careful with them newfangled calculators and things or you will hear about it from your prof.

In this exercise I’d say “near bout couple of dozen degrees, give or take a smidgen”.

my calculator goes to like 15 digits :expressionless:
and it also gives simplified radical answers… like if I do (sin 75) it gives me (√6 + √2)∕4 lol…my calculus teacher made me disable that function

I do plan on having precision, just not that much lol…
Im hoping we can get our fame up and designed before the end of next thursday…
then we can accomodate everyone elses mechanisms, and we can get it built…last year, we didnt have a working frame till week 5 :rolleyes: