# Why omni wheels on a thrower

Hello forum members,

I Have seen a lot of teams using Omni wheels as flywheels recently. I never tested it myself, because I just assumed it would allow for more play and less accuracy than a high traction tire. What effects (good and bad) have teams seen when using Omni wheels? Does it allow for less friction or more consistency?

Omni wheels have more traction than high traction wheels so people use them to ensure the most energy is transferred to the ball as possible. The consistency would be interesting thing to test because none of the really accurate/consistent flywheels I have seen use omni wheels.

Has anyone used omni wheels for single flywheel and if so, what was the resul .

A nearby team has used omni wheels for a single flywheel. He can get 3/4 court shots pretty accurately and has a video up on YouTube. It has a bunch of footage of shooting. We built this in late July, so it’s probably different now.

The only problem I have with omni wheels is that they’re only 4" in diameter, but I’ve heard that it’s pretty decent as there is no rubber that slips off.

What wheels are consistent? (that u have seen so far)

I have seen teams be consistent with a combo shooter that is a Omni-wheel on top of a traction wheel (it is a fly wheel shooter with two side but each side has two wheels) and my team has a pretty consistent shooter with a stacked shooter design using 5in traction wheels

i think teams have been doing that for momentum. because the balls don’t actually make contact with the traction wheel

You’ll notice that usually they are used in conjunction with other wheels. I think its purely to increase the rotational inertia of the flywheels, as you point out.

But also, doesn’t having a larger wheel increase the tangential velocity of the wheel at the same rate of rotation since the edge is farther away from the axis of rotation? For example, the edge of a 5" wheel has to travel a lot faster than the edge of a 4" wheel to do a single rotation in the same amount of time.

From what I’ve heard, one of the problems with using a traction wheel, particularly 5", is that the plastic tire will start to flex at high speeds, which is the reason 8059A has zipties on their flywheel. Has anyone else experienced this?

we did notice that happening, so we added rubber bands to help keep it all in place, however we removed the rubber bands, and although the tires to visibly flex at high speed we have not noticed it affecting our shooting

They use the 4 inch omni wheels to eliminate slippage of the rubber at high speeds. since the balls don’t contact the 4" traction wheel, they don’t need to secure it. 5" wheels have had problems on single wheel flywheels because of the more drastic speeds needed to fire the balls.

If by “they”, you mean 8059A, I don’t think they use 4" omni-wheels. I do agree that omniwheels have better traction and don’t have the flexing issue, but it’s also a trade-off because you’ll need more power to keep them spinning at a high enough rate to obtain the necessary tangential velocity. It’s anyone’s guess as to what the optimal configuration is (double or single, omni or traction, what angle to shoot at, etc.), but there are certainly trade-offs to almost every significant design choice.

I meant any team using a similar design. and yes you need a higher gear ratio but remember the wheels weigh less, so its less strain on the motors to speed it up and keep it rotating.

It sounds like the 5in wheels would have a shorter cool down time (the time in-between shots) because there is more momentum and a lower gear ratio, however I believe you are correct that start up takes more time and has more motor strain.

but smaller wheels can re accelerate much faster. so its a difficult trade off. i think one advantage of smaller wheels that large wheels can never make up for is that the entire robot weighs less. this can go a long way in lifting. So if there isn’t a significant difference in shooting abilities i would side with smaller wheels. also there is more space to build a lifting mechanism on the robot.

This is true, but remember, if you are looking for consistence, more rotational velocity is normally required. A heavier wheel also puts less strain on the motors because the wheel doesn’t lose a lot of speed after every shot. when you use a light wheel, the speed after every shot is slower, and you force the motor to pull more amps. You also have a better chance of tripping a breaker.

Because a heavier wheel doesn’t lose as much speed after every shot, you also don’t have to rely on having a really good PID to get your speed up to the optimal range every time, and can often throw at a faster rate. This is why baseball pitchers use big heavy tires to pitch the balls.

just my 2 cents.

One of our middle school teams just tested a prototype using omni wheels last night https://www.facebook.com/vexteamvirus and after shooting a couple balls, we found lots of orange “ball bits” on the practice field. So, high speed omni’s run the risk of destroying game elements and getting the robot DQ’ed.

Honestly most robots are going to spew at least some bits of foam, simply because all the flywheels have some sort of thing that can scrape the wheel. The omni wheel has the roller edges to scrape, the 4" traction wheel has the little shapes/ridges to scrape, the 5" traction wheel has the bumps on it to scrape, etc.

in my experience, the only time the omnis have make significant score marks on the balls was when there was a lot of slippage. If the ball was compressed the wheels didn’t “scrape” the ball.

On some of the flywheels I have seen, the wheels have attracted a yellow hue from the balls rubbing against the flywheels. It seems after each scrimmage the field is covered in little specks of coloured plastic…