Wheels: Metal or Plastic?

[thefro526]

We've used both metal and plastic wheels in some of our previous drivetrains and I haven't really noticed a functional advantage from either material.

Back in 2006 and 2007 we used the IFI High Traction wheels (Now sold under the VEX Pro brand) because they were one of the only COTS High Traction wheels at the time.

Since then we've used AM Kit Wheels and Plaction Wheels and all of them have held up fine. We'll probably continue to use Plaction Wheels in the future because of their low cost and durability.

I guess if we were making our own wheels we'd probably go with some sort of Aluminum though, just because we have more experience with it than plastics.

[JamesCH95]

Originally Posted by Chris is me

Making a wheel out of composites (carbon fiber) just seems excessive and difficult. It's just a wheel, no need to go overboard. Especially considering how the material fails when you drill into it for tread attachment and stuff.

I know that CF construction SEEMS difficult, but when you explore your options, gain a little experience working with composites, and perhaps settle on a design that isn't 100% carbon fiber you might realize that it's not so bad to work with.

[AdamHeard]

We won't be leaving aluminum anytime soon; Our wheels are very light, and the runtime on the CNC is pretty short.

[Chris is me]

Originally Posted by JamesCH95

I know that CF construction SEEMS difficult, but when you explore your options, gain a little experience working with composites, and perhaps settle on a design that isn't 100% carbon fiber you might realize that it's not so bad to work with.

Shaker has used pultruded fiberglass for two years; we know it works. It just seems simpler to buy wheels or to make them out of aluminium than to figure out a way to make them out of composite materials. We'll be happy to hook those AL wheels into a fiberglass frame, though.

[Lil' Lavery]

Originally Posted by Chris is me

Machining it from solid seems time consuming; I wonder how long it would take to make some with outer "plates" and AL tube though. I think 1625 does something like that.

That's not all that dissimilar to what the IFI traction wheels are.
And it's even more similar to how 612 used (still does?) make their wheels. Except they use(d) PVC rather than aluminum. They gave the wheels great reviews the first time they used them (2007, iirc) and I know they've used the concept again. I do remember a drive failure they had in the semi-finals at VCU in 2007, and it might have been a wheel, but I'm not sure.

I'm interested in a different take on composite wheels. Not wheels made from a "composite material" (carbon fiber, etc), but rather a wheel made from multiple materials. In order to reduce weight, many teams use less material in locations that experience less stress. I'm curious about using a different material in those locations could possibly lead to even greater weight reductions. Or course, this requires more machining and some system to attach the two materials, but it's an area that I don't think has really been explored yet.

[AdamHeard]

Originally Posted by Chris is me

Machining it from solid seems time consuming; I wonder how long it would take to make some with outer "plates" and AL tube though. I think 1625 does something like that.

It's been a while since I checked with the guys fabricating them, but with a CNC running at decent speeds the runtime for our wheels is less than 10 minutes, for sure.

[JamesCH95]

Originally Posted by Lil' Lavery

I'm interested in a different take on composite wheels. Not wheels made from a "composite material" (carbon fiber, etc), but rather a wheel made from multiple materials. In order to reduce weight, many teams use less material in locations that experience less stress. I'm curious about using a different material in those locations could possibly lead to even greater weight reductions. Or course, this requires more machining and some system to attach the two materials, but it's an area that I don't think has really been explored yet.

One could take some tubing, machine a rim profile into it, then use radially oriented bolts to connect it to a spider (hub and spokes) made of a different material. This eliminates the (IMHO) silly practice of milling a huge chunk of billet into a wheel, which is just not practical in the real world.

[Greg McKaskle]

When racing teams want to save weight on wheels, they go with magnesium or "mag wheels" -- similar to the cRIO housing.

Greg McKaskle

[Gdeaver]

Plaction wheels have worked well for us. However, more important than the hub is the material that touches the playing surface. The conveyor belting works but, we are looking into better materials. Has anyone tried other tread material that they like better than the conveyor belting?

[DonRotolo]

Originally Posted by Chris is me

It's just a wheel, no need to go overboard.

If I'm buying wheels, AM Plaction wheels are great. The right price point, they worked well this year, tread changing was easy enough, and light enough.

My original question was intended in the context of "buying" wheels, not fabricating them. They ARE just wheels.

Originally Posted by Lil' Lavery

I'm curious about using a different material in those locations could possibly lead to even greater weight reductions.

Or, for those concerned about the impact resistance of Carbon Fiber, how about some metal reinforcements in critical spots? If we were inclined to make wheels, this is the direction we'd be heading. A clear focus on the required capabilities of each part of the wheel, and then choosing the best material to meet those requirements, and finally figuring out how to join them together...

[AdamHeard]

Originally Posted by JamesCH95

One could take some tubing, machine a rim profile into it, then use radially oriented bolts to connect it to a spider (hub and spokes) made of a different material. This eliminates the (IMHO) silly practice of milling a huge chunk of billet into a wheel, which is just not practical in the real world.

Really?

There are many industries where machining a wheel from billet is *exactly* what they would do, hands down, everytime (it'd certainly be cheaper and faster than carbon fiber, which those same industries would also not hesitate to do).

For most mass production purposes, they might not be cost effective (really depends on the size, and the value to the user the wheels provide), but they easily could be.

Also, they're clearly cost effective for AndyMark, priced at a point verrrrry tempting for teams.

[JamesCH95]

Originally Posted by AdamHeard

Really?

There are many industries where machining a wheel from billet is *exactly* what they would do, hands down, everytime (it'd certainly be cheaper and faster than carbon fiber, which those same industries would also not hesitate to do).

For most mass production purposes, they might not be cost effective (really depends on the size, and the value to the user the wheels provide), but they easily could be.

Also, they're clearly cost effective for AndyMark, priced at a point verrrrry tempting for teams.

Can you please be specific about what those "many industries" are?

And AndyMark, an excellent company, supplies wheels almost exclusively to FRC (as far as I know they are not an OEM supplier to any manufacturer), and at $26/whack the performance wheels are far from cheap. The Skyway wheels (injection molded I believe) are less than half the cost with integral tread. If you were picking wheels for anything other than a 1-off robot you would definitely pick the skyway wheels over the "performance" wheels because they would be much more cost-effective.

Machining from solid chunks of metal is very costly because there is a large amount of wasted material and a lot of time is spent removing that material. These are both bad for your bottom line, and bad for your carbon footprint.

How many machines made in the real world use wheels machine from machined billet? Cars (including race cars), bicycles, airplanes, roller blades, skateboards, office chairs, commerical robots (i.e. packbot) etc. all seem to use wheels not machined from solid chunks of billet. Sure, you can buy car wheels machined from solid billet, but they're more expensive (by a factor of 2 or more) and heavier than forged wheels.

Machining wheels, or any part of reasonable size for that matter, from a solid material is typically found in 1-off, prototype, or development scenarios. I can't imagine these types of machines accounting for anything other than a very small fraction of any market.

[artdutra04]

Originally Posted by JamesCH95

Can you please be specific about what those "many industries" are?

And AndyMark, an excellent company, supplies wheels almost exclusively to FRC (as far as I know they are not an OEM supplier to any manufacturer), and at $26/whack the performance wheels are far from cheap. The Skyway wheels (injection molded I believe) are less than half the cost with integral tread. If you were picking wheels for anything other than a 1-off robot you would definitely pick the skyway wheels over the "performance" wheels because they would be much more cost-effective.

Machining from solid chunks of metal is very costly because there is a large amount of wasted material and a lot of time is spent removing that material. These are both bad for your bottom line, and bad for your carbon footprint.

How many machines made in the real world use wheels machine from machined billet? Cars (including race cars), bicycles, airplanes, roller blades, skateboards, office chairs, commerical robots (i.e. packbot) etc. all seem to use wheels not machined from solid chunks of billet. Sure, you can buy car wheels machined from solid billet, but they're more expensive (by a factor of 2 or more) and heavier than forged wheels.

Machining wheels, or any part of reasonable size for that matter, from a solid material is typically found in 1-off, prototype, or development scenarios. I can't imagine these types of machines accounting for anything other than a very small fraction of any market.

You'd be surprised at the amount of production-run items that are fabricated in machine shops on milling machines.

Go to any local machine shop, and chances are 99% of the parts there aren't onesies and twosies for prototyping, but rather part of a 50, 100, 500, 1000, or 10000 part production run. Why?

Injection molding is cheap, but it's not a universal solution. It's good for cheap, low-tolerance stuff. But there are a lot of components out there that require high-precision, high-tolerance components in order to function properly. For these parts, they are often fabricated in machine shops. But because these products are often industrial-to-commercial/industrial or industrial-to-military parts, you won't see them in Walmart anytime soon. But these products do exist, and they do keep machine shops humming.

But precision isn't the only reason that machine shops remain in business; often times injection molding or sandcasting is much more expensive than milling out of billet stock if you're talking about low-volume or intermittent product runs. Injection molding has a lot of tooling and setup costs, and doesn't become cheaper than milling until you're made quite a bit of parts.

And even then, a sizable chunk of business I've seen at a local machine shop was taking forged/sandcasted parts, and then milling critical features into it, like facing off flange surfaces, drilling and tapping mounting holes, etc.

Besides, there isn't that much of a waste from machining out of billet stock; the chips get recycled. That, and (without seeing numbers) I'd rate machining stock out of aluminum much higher than plastic injection molding on the environmental/CO2 scale. The former is infinitely recyclable and does not need petroleum as a basic ingredient, whereas the latter can only be "downcycled" a few times and needs petroleum-based hydrocarbons as a basic ingredient.


P.S. This post was typed up on a MacBook Pro computer, which has its entire frame/case milled from a billet of 7075 aluminum.

[Peter Matteson]

Originally Posted by Chris is me

Machining it from solid seems time consuming; I wonder how long it would take to make some with outer "plates" and AL tube though. I think 1625 does something like that.

Originally Posted by JamesCH95

One could take some tubing, machine a rim profile into it, then use radially oriented bolts to connect it to a spider (hub and spokes) made of a different material. This eliminates the (IMHO) silly practice of milling a huge chunk of billet into a wheel, which is just not practical in the real world.

177 has been do this since 2007 I have even posted several pictures on the forum showing how the design evolved.

We use 4" OD 1/8" wall 6061 tubing for the rim and 3/16" 6061 plate for the sides.

We actually put the rim profile in the pocketed side plates by having them extent past the tube, which makes assembly easier and reduces machining and rim weight.

I hope this saves anyone looking at doing this a few design iterations.

The evolution of how the wheels assembled:
http://www.chiefdelphi.com/media/photos/31102

View of the outside of the prototypes:
http://www.chiefdelphi.com/media/photos/31103

Wheel assembled with a lexan plate showing how it goes together:
http://www.chiefdelphi.com/media/photos/31105

Inside view of a wheel plate:
http://www.chiefdelphi.com/media/photos/31104

[JamesCH95]

I'm not saying that machining doesn't have it's place, I am also not saying that injection molding is end-all, be-all solution. Many parts do have some machine work done to them, but milling something out a solid piece of billet is generally inefficient.

The wheels Peter Matteson shows are a good example of a wheel with much less machine time invested, and much less wasted material than machining from solid billet.