I wanted to get all your opinion’s on whether it is better to have a four or six wheel drive for getting over the bump.
If there isn’t a clear winner (most likely), what are the pros and cons of each drive system.
I had a 4 motor, 6 wheel drive, with a 1:1 ratio on my heavy scissor lift. It went over the bump amazingly with less than an inch of clearance.
A four wheel drive is simpler but needs more clearance.
A six wheel drive hardly needs any clearance but the bot as a whole needs to be well balanced because the robot will rotate more as it traverses the bump.
A four wheel drive has more traction on the bump.
A six wheel drive has more traction on the ground.
4-wheel on Pillow Blocks is the best way to traverse the bump this year. You can’t get stuck, balance doesn’t matter and it’s easy to build. Mecanum and Omnis both work. I think we’ve done… 8 chassis this year. I really like Pillow Blocked 2:1 Mecanum, personally, but you have to give that a running start at the bump because you loose acceleration. 1.6:1 is fine, and the much safer option.
Too bad an X-Drive has issues. It would be so much better. But every one we built was either too slow, or burned out after a couple times crossing the bump after we geared it up. Maybe next year.
We’re going with 4 wheels mainly due to access with mecanum drive.
High traction and mobility caught our eye initially. It adds a bit more control in the driver period, but it also adds flexibility to autonomous. After prototyping, we found out it went over the bump like it doesn’t exist, so we had no reason to resort to a 6 wheel drive. We also got over the programming barrier pretty early into the season, so that wasn’t a handicap.
True, it’s an elevated drive, but due to our chain bar, our center of gravity isn’t as high as scissor lifts or linkage systems anyways. We never worried about tipping from the side because our drive train is wide and gravity’s centered. We never worried from tipping from the front because our lift would be there to right us. With poor driver control, we could tip from the back, but our chainbar also has the ability to right ourselves and continue playing. We added a rollguard to prevent tipping from the back, but we still need to test it.
Actually the traction is the same on the ground as the 4" traction wheels are slightly smaller than omnis. But you can put a large hs sprocket in for the high traction wheel. The gear makes it slightly bigger than the omnis causing better turning I believe.
We have four wheels with the chain wrapped so there’s an open space between them. Each wheel is mounted on its own bracket so we can literally un-bolt the bump from the field and slide it under the bot between the two wheels with no contact.
We used to have 6, and we noticed that they didn’t get over the bump as quickly as four.
This video pretty much sums up why I went with 4 wheels.
The main problem with a four wheel drive is being able to be pushed sideways during a match.
I agree in a match it has it’s downfalls, but I think the pros over-weigh the cons. Even if you are being pushed sideways, you can turn and push against them, or let them push you into a solid object and wait for the pinning count to start 
(first option is best). This drive train gets over the bump like a pro. We can get over in less than a 1.5 sec. It also straddles and un-straddles the bump very well. The 6-Wheel drive just takes way to long.
4-Wheel drive all the way.
Or you could just use the antigravity motors and call it a day
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there are ways around this:
mechanem wheels (I think I spelled that wrong)
I have been replacing the front wheels of my robot with regular 4" inch wheel since round-up and while changes the center of rotation (think driving a shopping cart backwards), it can have unforeseen advantages…
We tried this in Gateway, and it has some major disadvantages. When a team tries to push you sideways, it turns your wheels forwards and backwards. This means that if you try to drive straight as you are being pushed, it may stall your motors. And it’s “mecanum wheels.” 
Hooray for Google spell check (search).
In terms of 4 wheel vs 6 wheel: 4 wheel can get over the bump quicker if it is sufficiently raised. 6 wheel can be closer to the ground and be resistant to being pushed sideways while keeping the center of rotation at the center of the robot. It depends on what you value more; in VexU I’m planning on having one of each.
4 wheel is better, especially if you cut your c channels so you don’t have to use pillow blocks. Without pillow blocks it is low to the ground and basically can’t hit the bump due to the cuts in the c channels.
I don’t see anything wrong with using pillow blocks, really. My bot uses them on the drive and we haven’t had any problems thus far, 4 wheels or 6 wheels
Not wanting to cut metal is a big reason I went with 6 wheels. Our club is very limited on money and parts so cutting a section of an aluminum c channel. Was out of the question
After many challenges with either the motor breakers or cortex breakers tripping, we finally solved the issue by lightening up our back end by using aluminum and moving our towers and lift forward one notch. Machines now run like crazy without tripping out. We have four 393’s with an 18 to 18 chain drive. The chain actually rides over the bump and assists in getting over it. We put high speed gears in the 393’s. We also tried going with a 18 to 12 sprocket but had problems with tripping out once again. The machine did however fly for the short time before motors starting tripping. Went back to 18 to 18 on the sprockets. This machine scored a 70 in driver control skills prior to weight change. We think we can hit an 80. Only two events left to do so.
Our team has tried both designs and we’ve agreed that for our purposes a 6 wheel drive is better. Getting pushed sideways while stashing has been a big concern for us, and so we’d rather take a hit in the time it takes driving over the bump than in stashing efficiency during competitions.
That being said, a four wheel drive would work much better for driver/programming skills, when the robot isn’t contested at all.
At least, this is my logic. We haven’t tried mecanums this year, so who knows