Hi everyone! Trying to do some planning and research before the season starts, and I’m trying to see how much the typical drop is on the center wheels, assuming something like colson wheels. I’ve done some searching on the forum, but I haven’t been able to get an actual measurement, just everyone saying that you need to drop the center. I was curious just how much you have to drop it to turn while minimizing rocking.
And on a somewhat related note, do 8 wheel setups need a similar drop? With what I assume would be the center 4 wheels? Thanks
Typically, most teams have a center drop of 1/8" for a 6WD WCD. If you’re using versablocks, the center hole is offset 1/16", so just flip the middle one. In some games like stronghold, you should increase this center drop.
You’d definitely want to increase the center drop if you have pneumatic or other soft tires with some give.
The center drop for 8 wheels is usually the same as for 6.
The reason for the center drop is that if your wheelbase is as long or longer than your track width, you will not be able to turn because the “scrub” forces that keep you from turning are as large or larger than the drive forces trying to make you turn. Putting the extra wheels lets you drive on a wide wheelbase, while providing the front-to-back stability so your robot doesn’t fall on its back when you accelerate or its face when you stop.
With 6 wheels, you can stabilize your position for shooting in steady state by placing your center of gravity somewhat behind or ahead of the center axle.
If an 1/8th inch is two much rock and you need a more level robot a lot of teams have gotten away with 1/16th inch drop. The problem with this is you change your wheels (or treads) constantly all season. We have had problems in years past with 1/16in drop wearing down and causing us to turn very slowly. I’d stick with 1/8th unless it’s really a problem!
I will need to go back through and reread that thread. There was a lot of good discussion if I remember right.
Typical ranges are from 1/16th inch to as much a 1/4". Most settle in around 1/8th to 3/16ths (3 mm to 5 mm).
If your chassis and wheels are stiff, you can go with the smaller drop. If your chassis is a little flexible, then more. If your chassis is very flexible, you made need to put omnis on some of the corners to get it to turn nicely.
This is less of a big deal with the higher power drives.
