Is there a page that lists specs (either diameter or circumference) for these omni wheels?
https://www.vexrobotics.com/228-2536.html states these are “200mm” wheels but my roboteers have no idea what that number refers to, and I don’t want them to take my word for it.
I would assume diameter, but I don’t know 100%, so don’t take my word for it.
In EDR it’s diameter and I don’t think there would be a difference between the two. You could try estimating it by counting the holes in the picture and lining it up with another part with known length
On the page you linked, scroll to the bottom and choose ‘Kit Contents’. You will see the wheels described as 200mm Travel, which is the circumference.
All of the standard and omni-directional wheels in VEX IQ are designed with nominal metric circumferences (160 mm, 200 mm, 250 mm) to simplify autonomous path-planning math for younger elementary-age students. We named the wheels “Travel” instead of “Circumference”, as younger VEX IQ students may not have learned the the term circumference yet.
The standard VEX IQ wheels are 200 mm circumference, which also works out quite well to being almost exactly 5x VEX pitch / 2.5 inch diameter.
 The compliant “balloon” tires used in some HEXBUG VEX Robotics kits have nominal VEX IQ pitch-based diameters instead of nominal metric circumference, due to a different design requirement. Since balloon tires likely would be inconsistent in autonomous (if used on VIQC robot drivetrains), we instead designed all of the balloon tires to diameters that were 0.5x multiples of VEX pitch. This would allow us to mix and match tires of different sizes on the same model, while keeping the model level and parallel to the ground (think of how some tractors / construction vehicles have different size front and rear wheels).
That being said, the compliance of the larger balloon tires could make great intakes on VIQC robots, depending on the game object / challenge.
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