double or triple roller small omni wheels

double or triple roller small omni wheels

For those convinced by Rick Tyler’s arguments that smaller wheels are desireable because

  • they accelerate faster
  • stay out of the way of manipulators
  • lower CG

The single roller omni wheels are undesireable because

  • they are bumpy (bump from roller to roller)
  • don’t grip well
  • and sink below roller level into the foam with heavy robots.

Price can be 50% more than current small omni if necessary, but less than 2x.

I have always used the larger omni’s but I am interested in the smaller ones. Teams should be aware that you will have to gear these wheels in a manner in which you factor in the new 2.5" diameter.


The product folks at VEX have a list of “wanted products.” A little birdie in Texas tells me that the 2.75" deluxe omnis are somewhere on the list, but not at the top. So, I guess that’s good news and bad news! (I’ve been asking for them for a year.) Just so you all know – the product planners in Greenville do listen to what you ask for.

we have noticed as well
if your robot is too heavy
the rollers would actually be useless because (if used as holonomic) the plastic in between the rollers would SCRAPE against the ground

I would go with the larger because due to the size of the roller, the surface area that touches the ground on the larger ones is still more than the surface area of the doubled up smaller ones.

I would go with smaller omnis with something lighter that needs to sit/slide on the ground. For example, this year, some teams had omnis on their claws that allowed their claw to slide easily on the surface.

sorry for the thread revival
but WOW lego has really stepped it up!

btw does the new small omni have anything to do with this? :wink:
leak the photos already! :wink:

First - It’s perfectly fine to revive an old thread (in fact I can’t imagine why it wouldn’t preferred over starting a new one) so long as the revival adds new information.

Never apologize for being smart enough and polite enough to do 10 seconds of research and then adding to a existing discussion instead of spamming out a yet another 100% redundant post or thread on a topic.

Properly reviving a thread is a sign of intelligence in my book. It is evidence that the poster, be they 6 or 60, realizes that there is more to the world than what they have experienced personally in their short life. Science and wise societies build on previous results instead of ignoring them.

Second, boy-o-boy do those ever look bumpy; but they are snap-together LEGO pieces, so I guess that is the current state of the art in LEGO.

PS: Anyone want to start a pool on how long it will be before someone is nice enough to excitedly let us know (again) that the Mythbusters show once featured building a Vex robot? It’s been a while. I think we are overdue. :wink:

a total “gordonized” idea here,
but what if you TWIST an axle 45 degrees and stack two small omni wheels THAT way??? :wink:

Doesn’t even have to be 45 degrees, if you want. You could barely twist the axle at all to get it so the wheels take over for each other, and you could cut them like “jgraber” did, too so they take up about the same amount of space as one non-cut small omni wheel, as well as better performance/look.


love the shaved down omni’s :wink:
my mentor will strangle me alive 10 times if i did that :smiley:
btw, was that drive setup as “good” as the 4" omnis?
or “better” than the original ones?

from experience i have tried 3:1 (gear up) holo on small omnis (single layered ;))
but the weight was just too much and we scrapped it within 5 minutes of testing
because we knew that no matter how hard we tweak it, we cannot get it to preform as well as the 4" or even normal 2.75" tank drive

I would assume that they would be slightly less performance, due to the super small rollers, but I wouldn’t know for sure, we’ll have to get info from jgraber… :rolleyes: Although one thing he didn’t try was twisting the axle, so you may want to do some tests yourself. :wink:


The original small omnis have a single small roller, so they become ineffective as the weight of the robot presses the rollers into the foam so that the non-roller surfaces rub the foam. They work better on hard surfaces.
Shaving down the sides and stacking two with offset rollers is an attempt to make it work better by removing the non-roller surfaces. The flatbot double catapult was very light. Performance was so-so, speed seemed slower than direct drive 4" tank drive.
As usual, my brainstorms exceed my Craftsmanship, and my budget-pain-point for doing it better the next time.

Likely tradeoffs between the nice 4" Omni and imaginary smaller ones:

  • 4" have more traction and footprint per wheel, imporant for heavy bots
  • 4" omni have more rotational inertia, so they react more slowly
  • 4" omni are bulkier, taking more frame space, blocking intake space in frame
  • 4" omni won’t fit under the ladder for RoundUp.

Real small Omni may have different tradeoffs, depending on how they are built.
It would be nice if their axle hole were offset from the rollers, so you could stack them to get more roller offset.

SLOWER than 4" direct you say?
in the pic it is also geared up 3:1
did you change the ratio later on?

I’m assuming he means because of the weight of his robot, gearing up to 1:3 wasn’t able to preform as well as it could with a lighter robot. With a holonomic drive, you also lose some power, so a 1:3 (Geared up for greater speed.) heavy holonomic robot with the 2.75" omni wheels, may end up being slower than a 1:1 tank drive somewhat-light robot.


This is a great point. There have been very successful robots with 1:3 drives and 2.75" wheels, but they weren’t holonomic, and they were very light weight. I’m thinking of 418 and 575 in 2009 – both of which used six motors and weighed less than eight pounds. Weight is the enemy of VEX robots. (Mostly :slight_smile: )

Yes, I remember 575 in 2009. I believe, at the world championship one of our teams played a match with them and I remember watching in awe at their robot zipping around the field, winning the match against two other robots as ours sat barely moving, with a battery failure. :o


agree with jordan, we were AMAZED when we first saw it
(and attempted to copy the speed without the proper knowledge of double supported axles at that time :()
but 575 gave a deep impression on how important speed is
least we managed to do something similar in clean sweep
(3:1 4" tank drive :))
we had to lighten the robot a lot to make the top speed