Holonomic wheel spacing [POLL]

I’ve been working on a project. Actually several, as usual. This one involves 3D printing a robot. Dono if it’ll work (also don’t see why it wouldn’t), but that doesn’t matter because this is a design question, or poll actually.

I have two designs:

Design A, 4" wheels - 15.3" Center to Center

Design B, 2.75" wheels - 16.7" Center to Center

My question is pretty simple, based only on the spacing / size of the wheels, which design do you think would be a better generic VEX robotics platform?

Any elaboration / opinions would be appreciated, thanks!

I think that for the purpose of spacing, the smaller wheels are better for drive with the high speed motors, but for a generic design, the larger wheels are probably better because almost all teams have them already, and they would work with the regular motors better.

That’s a really good point as the smaller wheels demand both having the smaller omni wheels and using the turbo kit.

But the wheels are larger and spaced fairly inwards, in this particular design.

I’d love to see which of these design tradeoffs win out.

I’m assuming that as a generic Vex robotics platform it would be used as a part of a robot, thus needing space for the other sub systems of the robot. In this case I think that the smaller wheeled robot would be better, as it allows more space for other systems in the middle of the robot.
I also think that the 3rd option in the poll has merit. As neither drive makes full use of the 18" limit(s).
In addition I agree with what Inspector Gadget has to say about the large Omni wheels.

Personally I would prefer the 4" wheels, mostly because they are a lot thinner than the 2.75" and a lot easier to fit onto a drive train. Another plus is the use of torque motors instead of having to switch out gears. It’s almost as fast as the 2.75" on high speed.

Objectively, the smaller wheels have less moment of inertia, meaning faster acceleration…

I have found that 2.75" wheels on a heavy robot (my robot was 30lb) are really bad because the 2.75" wheels do not roll as well as 4" wheels. When in a x drive configuration this is even worse.
Unless this 3d printed robot will be light, i recommend 4" omni’s.

Although I feel like if this drive is going to reflect vrc robots the wheelbase is too small in both designs.

I can confirm. This year with the robots being bigger and heavier, the smaller wheels sink into the tiles more and don’t turn as well as the larger 4" wheels. If you have a relatively light robot, the 2.75" wheels will be fine.

I just had state and I saw quite a few small-base robots tip over, which means a bigger base is good for stability. However, at the same time, our robot was nearly 17.5" long, and we had trouble getting into between the wall and the skyrise base to get more skyrise sections.

Assuming you can stay centered with the weight overall and you can get high speed gearing working, the bigger wheels are more optimal. Good acceleration, but poor top speed.

Can the reduced size opening hinder the game play? The needs of the rest of the robot can dictate the base choice too.

However, smaller wheels give more placement options and control.

I can’t show one of our guys from this year yet. Maybe next week. (80Y) They use the new third option - the medium size omnis!

Small wheel example in the X drive 81M Mystique in Sack Attack. (Yes it turned very nicely) This was option B in your other thread.



An oldie but goodie - team 81 Gambit in Round Up. Big wheels and a snorkel in your design A.


Which was inspired by KTOR back in the day. (Minus the hair)


I was in KTOR’s pit through most of the Round Up World Championship, it’s entirely possible that I was just right of this camera’s view when that photo of Andrew Adaman was taken.

I’ve never used the 2.75" wheels, do they really have issues?

I’m not a big fan. They are pretty wide and the X drives I’ve seen using them seem to have problems. We tried a comparison of 4" high speed vs 2.74 turbo on a tank drive competition robot and the 4" setup far out-performed the small wheel setup. The 3.25" omnis are really incredible though; really thin, smooth and able to put different inserts in saves a ton of time putting lock bars.

There are two types of 2.75" wheels

These work fine. Top speed is the issue here:

These are junk and sink into the mats:

The 3.25" ones work well so far this year too. Only one issue with an omni falling off one but that can happen on any of them. The team that did it are heavy drivers.

And the 4" ones…