Re: Wheels: Metal or Plastic?
 

[off topic]

A big up and coming thing right now are bioplastics like PLA (polylactic acid), which are made from corn as opposed to being petroleum based.

I've tried to introduce these types of earth-friendly plastics into a bunch of the projects I've been apart of.

PLA

Bioplastic

[/off topic]

-Brando

Re: Wheels: Metal or Plastic?
 

Thanks a lot for posting this. This method is really cool and something I'd like to try and duplicate this year.

One question: Are the side plates held on with a press fit in the last iteration, or are they eventually welded?

Re: Wheels: Metal or Plastic?
 

While they are a slight press to assemble the final hold is a series of fillet welds along the lightening pattern of holes. The lightening holes expose the edge of the tube to facilitate this.

This years modifications included adding hex drive hubs to some of the wheels.

Also the miss-alignment of the lightening patterns on both sides is to provide tool clearance to get a ratchet inside the wheel to add a lock nut if the threading in the Al side plates is stripped.

Re: Wheels: Metal or Plastic?
 

Aerospace companies and defense contracts would not hesitate to machine from billet.

There is a Packbot wheel sitting on my desk, it's machined from solid plastic in a very process that requires multiple ops.

Re: Wheels: Metal or Plastic?
 

Oh, great. Instead of making things out of fuel, make them out of food? Yeah, that's a big help. Now instead of just making a luxury like energy more expensive, now everyone ends up having to pay more in order to do something absolutely vital like eating. :P

I'm [mostly] joking, of course. Renewable resources are almost always better than fossil ones, and disruption to the food economy from corn-based ethanol production has pretty much been worked out by now.

Re: Wheels: Metal or Plastic?
 

True, some parts are machined from billet when they have to be. Though those are two industries known for spending quite a bit of money.

Re: Wheels: Metal or Plastic?
 

Considering the amount of land devoted to the production of corn, the solution is arguably not-that-much better. Now, if they could reduce the ammount of corn-based blah in our food supply, replace it with natural stuff (such as cane-derived sucrose instead of high fructose corn syrup), and remembered the revolutionary practice of crop rotation, we could have better tasting, more diverse food and whatever corn isn't sold as corn could be used just for a select few applications such as the production of bioplastics and ethanol.

On the topic of wheels, small wheels for light duty applications can be easily made from layered disks of strong corrugated cardboard (shoeboxes made of corrugated cardboard are often made out of 'strong' material [the edges and corners don't crush easily]). If properly laminated and reinforced**** & covered with roughtop or wedge top, this design could be somewhat competative with other wheels, particularly those around or below 4 inches in diameter.

**** Honestly, lamination and reinforcement is probably the what will doom every attempt to implement this, but I could be wrong. Integrating lexan, nylon, fabric, carbon fiber, etc. into the design could help.

To give anyone who looks into this a tip, look into tripple layered corrugated cardboardike the kind used to ship large items such as pianos (some where I heard about a cardboard boat that was rather successfull and made out of the stuff. The people who ran the team owned a piano shop.

EDIT: I should probably have mentione that direct attatchment to the axle is a bad idea for these wheels, the bore would probably get destroyed. Using some sort of hub to distributre the stress around the wheel should be a much better solution.

Re: Wheels: Metal or Plastic?
 

Peter, how do you hold your sprockets and bearings in place on those wheels?
Thanks
Bruce

Re: Wheels: Metal or Plastic?
 

This decision depends on the game but personally, I will always go with alumnium for wheels over plastic, especially with terrain obstacles. This is for a variety of reasons but mostly becuase our drivers beat up our robots and we find alumnium just holds up better. Not saying that ABS or UHMW won't hold up becuase I've personally used both and seen other teams use them perfectly. Generally, we'd rather not take a chance on failure in our drivetrains and like to over engineer them. We've had only 2 drivetrain in match faliures in 3 yrs. 2008 nothing went wrong (in fact that dt would still be in tact with the original chain installed 01/08 had we not dissasembled it.), 2009 we lost a chain once, and in 2010 we had one of our tracks break but it was due to manufacturer defect. As far as the material on the wheels, we like the wedgetop, but have tried gum rubber and roughtop. Wedgetop while not the higest friction of them all is easier to get on the wheels then the gum rubber and the friction diffrence between roughtop and wedgetop is pretty much negligible from the data I've seen.

-Drew D.

Re: Wheels: Metal or Plastic?
 

We used a press fit and then designed our wheel spacers to ride against the inner race as a back up. It was really basic but easy to assemble.

Re: Wheels: Metal or Plastic?
 

Don,
Our history with IFI alum. wheels and AM plaxtion wheels sounds pretty similar to yours. Aside from all the discussion about materials and homemade wheels, to your original question, I would have to say after using plaction this year, we prefer them. They took an incredible pounding with the way we often came off the bump, and held up to shocks that I think would have bent an IFI wheel. The slight compliance of the plastic makes the bearing press-fit a breeze, no tweeking the hole size. The split assembly means you can easily widen the wheel to any width you want, not limited to stock widths. If you cut your own treads from bulk belt like we do, that is nice. Clamping a slightly over-width tread between the wheel halves really locks it in. No tedious assembly of the wheel, and it doesn't fall to pieces when you remove the screws. Yes, it may be slightly harder to rivet through the thick rim (although plastic is easier to drill), but 1/2" long rivets carefully located between spokes workes just fine.

So let's see.....lighter, cheaper, stronger, variable width, easy bearing fits, no assembly. Plaction.

Re: Wheels: Metal or Plastic?
 

Where do you get your bulk belting and how do you cut it to width?
Bruce

Re: Wheels: Metal or Plastic?
 

Mcmaster search "incline conveyor belting"
and tread down on a horizontal bandsaw works great for us

Re: Wheels: Metal or Plastic?
 

Bingo Aren.

This stuff http://www.mcmaster.com/#incline-conveyor-belts/=9gagfi cut on a bandsaw with a wood blade

Re: Wheels: Metal or Plastic?
 

We typically cut our tread on a table saw, but have used bandsaws and even a foot-actuated sheet metal shear in the past (with mixed results).
I believe Pink (233) cuts its tread on a waterjet.