Help with Omni wheels?
 

Our team is considering using some omni wheels this year, but we haven't used them in a few years, so we don't know what's up.

Does anybody know what the best, most effective onmi wheel is out there?

Re: Omni wheels?
 

AndyMark has a lot of different omni-wheel options, from aluminum omni wheels, to the "coolie-dualies", to the molded plastic wheels.

But if you want even smaller diameter omni wheels than is offered by Andymark, check out the "transwheels" at omniwheel.com.

Re: Omni wheels?
 

Thanks, those help me get a visual!

A question though...I saw a team last year that had these really sweet looking omni wheels in which the little wheels were at an angle, which made the forward moving more smooth they said. Does anyone know where I can get those?

Re: Omni wheels?
 

be careful what you chose, a few years back, my team had rubber omni wheels, worked great on a hrad surface, but on carpet, the bot wouldn't move....

Re: Omni wheels?
 

Might be mecanums. If so, AndyMark has 'em.

Re: Omni wheels?
 

I believe the wheels you are talking about are mecanum wheels. These too are available at andymark.biz.

Re: Omni wheels?
 

does anyone feel that there will be a big benefit this year to using an omni wheel? I haven't decided yet whether it will be more crucial to have a strong pushing system rather than a quick maneuverable one.

Re: Omni wheels?
 

Our team has quite an interest in omni wheels for this year's game. They decided to look at omni wheels from airtrax. The movie that pops up on the home page are the ones we really like. Check those out too.

Re: Omni wheels?
 

Judging by their scale, they look 14" to 18" in diameter. :ahh:

Re: Omni wheels?
 

our team used mechanum last year. we found they were more effective than omni.

Re: Omni wheels?
 

I agree with her...
Mecanum Wheels is more efficient than other omni wheels...
I always wanted to use this type of wheel in my team but i never used because don't have these wheels in Brasil... so we have to import and it's not simple here...

Good Luck teams

Re: Omni wheels?
 

unless airtrax makes custom wheels those look way to big and heavy for our robots. The technology is amazing though.

Re: Omni wheels?
 

I would suggest to buy metal omniwheels instead of the plastic ones. Our first year with omniwheels we bought the plastic ones, and they broke to pieces during the course of a regional.

Re: Omni wheels?
 

Not only are they stronger, but if you bend them up during rough play, they can easily be bent back and used again.

Re: Omni wheels?
 

We have used AM plastic wheel for the last two years. In 4 regionals, 2 IRI's, 1 championship, and hundreds of hours of demonstrations we have never had a single failure.

Re: Omni wheels?
 

Although mecanum wheel provide excellent mobility and a relatively fast movement speed, the system to make them work weighs too much. Each wheel weighs about 2.5 pounds + 2.5" CIM Motor + transmission = alot of weight simply to make the robot move

Re: Omni wheels?
 

our team was considering using omni wheels, but it would be hard to herd/move the balls out of the way. Of course, I guess the reason to use omni wheels is so you can juts go around quickly :D

Re: Omni wheels?
 

Yes, that first year, I thought that it was a good idea to put a 10% fiberglass fill into the black polycarbonate. While that made the tensile strength higher, it was lower rated on the Izod impact rating. The fiberglass mad the material brittle, and when teams hit the side of the 1 point ramp in 2006, the wheels broke. The result of these breaks were improving these wheels and creating the aluminum omni wheels.

So... last year we had black polycarbonate with no fiberglass filler, and that resulted in zero complaints about breakages.

If I had to pick which omni wheel to use on a FRC robot, I would choose the 6" aluminum omni wheel, and use an Omni Spacer to make them a dualie omni wheel. That is a sweet setup. The polycarbonate wheels are nice, and can handle 2 bearings, but the aluminum wheels take up less space (they are thinner) and they are repairable. The only negative about the aluminum omni wheels is that they only have the ability to have 1 bearing mounted to them, that is unless you add on an extra hub.

Andy B.

Re: Omni wheels?
 

Last year we used the plastic polycarbonate omni wheels and we are a very happy customer. Zero problems. In fact we are ordering more for this year tomorrow.

Re: Omni wheels?
 

In 2006 I helped create an omni drivetrain for team 859 using the poly AndyMark omniwheels, only to have the roller mounts (around the circumference of the wheel) shatter several times on the ramp. Other teams had better luck with small caster-style wheels such as from omniwheels.com or mechanum (angled roller) wheels.
At least without ramps this year's game should be easier on omniwheels. :]

Re: Omni wheels?
 

We used the AM plastic omniwheels last year with absolutely no problems.
We will have to replace the rollers because in the course of 2 regionals and the championships, we wore them down...

this year we are going to a new idea.. using two of the poly wheels staggered to produce a wider wheel.

Please take a look a the attached jpg ... we are direct driving the omniwheels with Dewalt transmissions...

This is a holonomic robot....

Re: Omni wheels?
 

what are the benefits of direct driving the omni wheels instead of using two normal wheels and two omni in the front?

Re: Omni wheels?
 

In my years of robotics i havent found an advantage to driving omniwheels other that more power.

Re: Omni wheels?
 

When you say they are more affective, is that just for versitility in moving the robot (more or less why they are designed this way) or are they also affective for top speed?

Re: Omni wheels?
 

I have only seen one advantage of powering omni wheels, to climb things like in the 04 game.

here is a picture of my old hs bot from the 04 game with my omni wheels in the front so we could turn easily and climb the steps without a problem. it was really fun to watch actually.

Re: Help with Omni wheels?
 

Our team has been thinking about using an omni drive but we have a question. How do you figure out how fest an omni drive will go. Our team knows how to calculate the speed if all the wheels are strait, but how do you account for the omni wheel slipping?

Thanks

Re: Omni wheels?
 

That is going to be one really fast robot! :ahh:

Re: Help with Omni wheels?
 

i have never used omni wheels but my team is thinking about it. What is the difference between metal and plastic wheels on the carpet? Does one work better than another?

Re: Help with Omni wheels?
 

Quick answer: metal wheels are not allowed. All the omni wheels in this competition have plastic rollers. So the main difference would be weight, I think.

Re: Omni wheels?
 

I agree dual 6" aluminum omniwheels are sweet. In '06 my team spent a lot of effort building our own, so it was nice to have the option of buying them from AndyMark last year.

Our '07 chassis used single 6" aluminum AM omniwheels on the corners of a 6WD kitbot, and kit AM wheels in the middle with one CIM per side -- not a defense-oriented drivetrain, but nice for maneuvering. To get around the single bearing limitation Andy mentioned above, we mounted the inboard bearings in the sprockets that drove each omniwheel. This required boring out the center hole in the sprocket to 1.125", which is a relatively easy lathe operation in a standard 3-jaw chuck if the tooth count is a multiple of three.

Re: Help with Omni wheels?
 

Our team used two omniwheels in the front and two driven traction wheels in the back. The only problem with it was we could not get the omnis to stop turning when we wanted them to. This resulted in the front of the robot continuing to spin after we expected it to. Also, although they were very manuverable, another disadvantage that it was nearly impossible to go straight.

Re: Help with Omni wheels?
 

thanks for the help that will definately help our plans

Re: Omni wheels?
 

WE shattered a junky plastic one all over the field tw years back... and another one demonstrating post-season. The ones currently on the robot aren't very "omni" as most of the small wheels are locked in place by what I assume is a crushing force of the omniwheel plastic colapsing.


That said, last year we used these: http://andymark.biz/am-0097.html
with excellent results, and we will use them again in the future...

Re: Help with Omni wheels?
 

I wouldn't say mecanum wheels are better than omni wheels, they are quite different and transfer power differently to the movement of the bot, but I wouldn't call them better, I find the biggest thing about having a strafing bot, is to make sure your driving practices, and uses all the advantages the wheels give you (too often do I see a bot with mecanums or omnis being driving like a 4wd bot, I dislike it lol)

for the record omni and mecanums have slightly different pros and cons about them and depending on how you want to drive it or how skilled your driver is at controlling them, ethier one could seem "better" than the other for your team, I personally perfer omns over mecanums!

Re: Help with Omni wheels?
 

Driving Straight is definitely possible with omnis. Arc turning with two back omni can cause your back two omni wheels to fishtail moderately making the robot more difficult to drive. FRC#494 in 2006 used omnis in the corners instead of two omnis on the back side to help control fishtailing. Read the full report on page 160 of the 2006 FIRST Robotics Book.

Re: Help with Omni wheels?
 

It sounds like you might have the center of gravity of your robot too far forward for easy controllability. Putting it closer to the traction wheels would help things a lot.

When I joined the TechnoKats as a mentor, my first real programming challenge was to compensate in software for exactly this situation. The code detected the rear wheels' rotation (Banner optical sensors pointing at alternating reflective/nonreflective sections of hub) and adjusted the relative power to the left and right side motors in order to keep the wheel speeds consistent for perfectly straight travel.