4 inch Wheel of Doom


This is one of our new 4 wheels that we are testing out for the upcoming season. It uses the AndyMark sprocket bolt pattern. The material used for this wheel is HDPE and we are going to make a 7068 aluminum copy of this. The software used for this wheel is Solidworks and MasterCAM. SO what do you guys think?


added pics!

Why are you considering making it out of 7068? That would be rather expensive. Is there some reason 6061 won’t suffice?

7068 is a waste of money. I’d hate to even think about how much it’d cost for 4+" round, or 4+" plate even.

Last year a company in madera went from using aluminum to titanium. So they gave us 20 6ft. of 2x2 and 1x2 aluminum and all the rod stock they had. That inlcuded 3030, 6061, 2024 and 7068. So we are using it since itz free. No other reason guys. :yikes:

what is your tractive surface plan? Lots of other custom wheels have a lip on the rim for adding lateral support to rough top. What are your plans?

If that was the case, personally I’d sell almost all of the 7068 and use that money to buy 6061 (or 5052*).

  • For sheet metal applications.

It may be free in terms of what you are paying, but it does still count against your BOM budget. I don’t know if your team usually comes close to spending that much on the robot each year or not (my team hasn’t been very close yet) but it is something to keep in mind.

We are usually under the BOM budget, btw Art that is a good idea.

Out of curiosity, why would you even go with aluminum if you have that much material on the wheel? Aluminum is much stronger than teams give it credit for, especially when used in circles for a wheel-type application. You could easily take out about half that material and still be plenty strong.

Really, right now i have in the middle a quarter of an inch and on each side a 1/8 face extra on each side, how much more do you wanna lose??

Looking through CD media, there’s a few examples. For example, one team’s wheel that I saw had an enormous amount of material taken out of it. I’m sure you could PM the creator and find out how the wheel performed.

[jk] Don’t set your sight on a new wheel design just yet rc, as Bill said. Knowing Dave, the robot this year won’t even require wheels :wink: [/jk]

I could honestly see stairs (or at least ramps) coming back into play. It’s been far too long with a smooth, uneventful flat playing surface.

Lightbulb, pnuematic casters.

The designer of those wheels decided to leave the community and cut off all contact; I doubt he’d reply.

Why wouldn’t you just stick with HDPE for the wheels. The weight savings is pretty huge and hdpe or UHMW is more than strong enough for the task.

Sdcantrell, I was not sure if UHMW was strong enough for the application. What other materials are strong enough for the application and lighter than aluminum? Plastics?? (McMaster Carr #'s Help)

Thanks everyone.:smiley:

You have to stop and separate the material strength and the shape/design of the wheel. You could make wheel designs where probably even glass is strong enough, and you can make wheel designs where only extremely strong steels and titaniums would be strong enough.

It’s not a simple matter of saying, okay, we have a wheel designed, lets just make it out of 7068. That may work in this case, but is extreme overkill. In the workforce, if you immediately jumped to a more expensive material (compare the cost of 6061 vs 7068) , you’d probably be out of a job really quick.

I think, rather than trying to pick a material to suit this specific wheel design. Lets start over with an entirely new wheel design. First, pick the material, as it’s much easier to design around a known material rather than designing a part and going “oh, I guess material XYXY” would be strong enough (and if it is, it might not be the most efficient way).

So, lets make a wheel. A real efficient design, not much heavier than it needs to be, not much more expensive than it needs to be, not more difficult to make than it needs to be (much leaves room for safety).

Okay, so in this new wheel design lets imagine the kind of stresses put on the wheel. First, you have the weight of the robot pushing from the point of contact to the hub. Second, you have the torque being transferred from the hub to the outer surface of the wheel. Finally, let’s just lump in all the random forces that will happen in a match; wheel getting hit from the side, robot being twisted which would twist the wheel as well, and so on.

Now, in an ideal world you’d have an engineer on your team would know how to reasonably approximate these forces, and use a method of testing the wheel design to make sure it can withstand them (plus a safety factor). Now, you can do what I did in high school and just run Cosmos on it; but when you get older you’ll realize that yeah, I got cosmos to run and give me an answer and a nice purdy graph, but in the end I had No Idea what I was doing really, and have no idea if those answers were reliable. Now that I’ve had classes that have covered some of those concepts, it really shows me how ignorant I was.

^If you have one of those engineers, go ask for his help now, and maybe stop reading the rest of this post.

So, assuming you don’t we have to go assumptions; luckily there is a huge sample size of wheels that have been tested through a season for you to look at (as most robots have been wheeled pretty much since FIRST started). Look at some of the more efficient designs people have used and try to analyze what they did. Was the shape efficient at transferring the robots weight from hub to floor? Was it efficient at transferring the torque? What is it efficient at surviving the rigors of a competition?

The best example I can think of is 254/968 the past two years. For 2008, they weren’t any fancy material, just plain 'ol 6061 and they worked.

Sooooooooooooooooooo… Now that you understand what the wheel has to survive, and what has/hasn’t worked and how efficient it was/wasn’t; Make us an improved wheel.

You’ve obviously proven you have the Solidworks Skills (which can be quite difficult for some people), now lets get those design skills developed real well. You’ve got potential, but you’ve got to stop and think about how you can realize it.

Adam, I understand where you’re coming from. First of all the wheel was designed around 6063, because that is what we had laying around. The safety factor was about 16 with all the proper forces included (an engineer helped with all that). Then a random sponsor donated some really cool material, 7068. So we decided to make it out of that, we were going to take out more material. But a couple of fellow members from other teams asked the question “Why not plastic?” So we as a team figured that plastic would be a lot lighter but none of us really have ever worked with plastics. Also when using plastic, you need to add material. Adding or subtracting material is not the issue here. I have looked up some specs on plastic but wanted some people or teams opinion on what type of plastic they used and how it worked out for them.

Thanks Adam for the concern