AM Coolie-Dualies VS Alum. Omnis?

[lynca]

I'm looking for similar advice. I used the coolie dualies last year with great success. The coolie dualies were designed after the Molded plastic wheels. Many of the teams I see using the molded plastic wheels use two of the molded plastic wheels offset so a roller is always coming in contact.

The coolie dualies replace the concept of two offset molded plastic wheel for half the weight and price.

I have not used the plastic molded wheels, so I am also interested in team's experiences with the molded plastic omnis as well as the Alum. Omni.

[Greg Needel]

I have used both the aluminum omnis and the plastic ones, I recommend the plastic ones over the coolie dualies or aluminum just because of bearings. The molded omnis hold 2 bearings in for full support while both of the other kind require you to put a bearing in the attached sprocket. Just for ease of use the molded ones save you the trouble of finding flanged R6 or R8 Bearings.

[lynca]

Thanks for the heads up on the dual bearings for the plastic molded. The Aluminum wheels state they can handle one bearing but I would imagine that is too much stress on the bearing. Last year with the coolie dualies, we used pillow blocks and directly mounted the coolies to the shaft.

[lynca]

I found a picture from the 2006 FIRST Book, page 88, FRC#123

[Greg Needel]

Originally Posted by lynca

I found a picture from the 2006 FIRST Book, page 88, FRC#123
]

That was a common problem on the first rev of the wheels due to over tightening of the screws that held the sections together, which caused cracking of the plastic. Since then the plastic has been and the torque specs of the bolts was reduced. I didn't hear of anyone breaking them in the 2007 season.


As for the bearing issue, Each wheel needs to have 2 bearings to support it, otherwise your wheel becomes an cantilevered load on your axle creating a moment with the possibility to bend your shaft or the wheel in the worst case. And best case is that your wheel will wobble.

[Barry Bonzack]

What about how bumpy the rides were in previous years with different designs? Have any teams attempted over 13 fps on the molder plastic and alumninum wheels or the coolie dualies?

[lynca]

I think the failures to the Plastic Omni were for one year only According to Andy Baker,

Originally Posted by Andy Baker

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.

From this Thread
http://www.chiefdelphi.com/forums/sh...t=plastic+omni