What Is the Best Wheel to Use

We are questioning what kind of wheels we need, we mostly think the tank wheels but we don’t have much experience with any of the wheels so we could use the help.

Use full omni. Some people are using traction and omni combos, but I’ve found that it doesn’t really help pushing, just makes you rotate around your traction wheels when somebody pushes you rather than go directly sideways.

Great, but would the tractor wheels help with steering?

It depends on your goals. Do you intend to climb? Then you will want to select wheels and build your chassis such that you don’t bottom out while climbing.

Do you have space to build a gear train, or do you need maximum acceleration? Smaller wheels can accelerate marginally faster, as they have less rotational inertia (i.e. it’s easier to get them spinning), but have a lower top speed for the same gear ratio. A gear train can overcome that limitation, but it takes space and build time. Similarly, do you need to push other bots? Smaller wheels can give you more torque (a key factor in pushing power) at the expense of top speed without building a gear train.

As for omni-wheels vs. solid wheels, using only a single pair of solid wheels gives you control over your robot’s center of rotation. A pair of solid wheels on the front and a pair of omniwheels on the back is usually preferred for robots that have manipulators on the front, as it moves the center of rotation closer to the end effector.

As for some of your terminology, I’m not entirely sure what you mean by tank wheels or tractor wheels.

4 in traction?

The VEX 4" traction wheels have less traction than the 4" omnis. They are pretty bad. If you are using 4" wheels I would recommend doing a 6 wheel drive with the rollers in the center omnis screwed in. This provides immense sideways traction. The rest of the wheels can be omnis

Do they? Or is that only on certain surfaces? The tiles are relatively mushy, which enables omnis to catch well with the edges of the rollers. But do they grip lexan better, for example.

@callen it’s something of a distinction without a difference, as coefficients of friction are interface specific. It’s entirely possible for one wheel to be slippier on one surface compared to another wheel yet grippier on a different surface compared to the same other wheel. And as people have observed, things get weird when one surface is compressible. So if we’re just talking about field tiles, we can say one wheel or another is grippier. All bets are off when we don’t hold at least one side of the friction interface as a constant, though.

They do from my experience and what seems to be the general consensus of the community. I would venture to guess it’s just because the 4" traction wheels are really poorly made.

I think the only way to solve the dilemma between which configuration and wheels are better is to introduce the all-powerful, best type of drive. I present to you, the
** * ## T A N K T R E A D S W E R V E D R I V E * **
tank tread swerve.jpg

Don’t copy my robot like that

Hey VexU meta right there

Our team decided to use a combination of omni and tract wheel. Which pair should be in the back and which pair should be in the front. Was this ultimately a good decision?

@Worst Robot Our team’s drive uses a combination of omni and traction wheels. 2 omnis in the front and 2 middle traction wheels and 2 back tractions wheels. This is a 4 393 motor base, with the front and the back wheels driven and a chain assembly between the middle wheels and the front wheels. Idk if this is the most effective base for parking, but it gets on the platform and holds its own really well.

I think the best would be a combination of 4" omni and 4" traction with the traction in the middle and the omnis in the front and back.

I agree with this. The traction wheels will give a lot of stability with holding their ground on the platforms and the omnis on the corners will easily slide to minimize friction while turning.

“Rollers screwed in…” Please elaborate. I’m sure I just don’t understand the wheel and rollers, but I don’t understand what this means. I didn’t realize these could be modified.

He probably means this:

Thanks! Tricky…

We used the locked omnis in with out first robot this season, we ended up calling them bling wheels…

Rahul