custom wheels
 

I noticed that a lot of teams are using custom wheels this year. Is there any advantages? What about costs? And what is needed when designing a wheel?

Re: custom wheels
 

We almost made our own wheels this year, unfortunately we had to return our 3D printer before we could finish them. Some advantages would be that you can make the wheels any size you would like as long as they remain within the constraints of the 3D printer. You can also change the structure of the wheel potentially saving weight.

When designing a wheel you would need a CAD software compatible with your 3D printer as well as some tread to attach to the wheel once they have finished printing. If I have some time later tonight I will upload an image of our CADed wheels.

Cost wise, you have a pretty large start-up fee. A 3D printer can cost you more then an entire team's budget for one year.

Re: custom wheels
 

Custom wheels are usually made in two ways: 3D printing or CNC machining. The 3D printing method tends to be the easier method. I've heard they can be really strong if made right, so you probably want to experiment before the season if you chose this method. From what I've heard, CNC'd wheels tends to be resource consuming, but you come out with a strong, light wheel.

Re: custom wheels
 

COLSONS FTW!

Re: custom wheels
 

Find a sponsor with a CNC mill (thanks GEMS!).

Shamelessly borrow AM's 6" performance wheel CAD design (the old one without the big hole in it for the zip-tied tread) minus a few features.

Buy 5.75" aluminum wheel blanks for about $9.50 each.

Turn your sponsor loose.

Finish up the tread grooves and rivet holes yourself.

Save lots of money.

Re: custom wheels
 

This is really inefficient.

Sure, you save money, but at the expense of sponsor's time.

I'm sure that sponsors time could be better spent on other robot parts.

We run COTS wheels now, after machining aluminum solid wheels for years.

Re: custom wheels
 

I'm sure you know nothing about our program or our sponsor. :)

I'm sure they are happy to save us money doing a part they can setup once and make repeatedly and relatively quickly, giving them more time to handle their very busy workload on all that fun stuff that *actually makes them money*.

I'm sure they are also happy that they saved 3193 money as well making the same wheels.

I'm sure we had another local CNC sponsor who is more flexible in making a variety of parts for us.

I'm sure COTS wheels weren't something we wanted to use on the competition robot this year.

Re: custom wheels
 

I'm sure you know exactly how to save your sponsors time and money and maybe I'll get to hear that someday....


Regardless, I agree with Adam that making your own wheels can be a resource hog for a lot of teams. Sometimes, it is feasible for a team to machine their own wheels, but even if I had the time/materials, I'd still think twice about doing it unless theres a significant advantage.

Some significant advantages can include the method of tred attachment, the way you attache sprockets for chain/belt, the exact diameter of the wheel and the width of the wheel. I dont think weight savings would be too big a motivation for making custom wheels. It really just depends on your teams resources. There are a lot of good wheels that are cots parts so i wouldn't worry too much about custom ones.

Re: custom wheels
 

Saving money is a significant advantage in my books.

Re: custom wheels
 

Versa traction wheels are cheap.

Re: custom wheels
 

Read Travis' list again.

A lot of people in this thread are assuming that what works for their team works for every team.

Re: custom wheels
 

I realize what works for one team doesn't work for every team. That said, for the majority of teams the time to make custom wheels is not worth it(as Chinmay perfectly stated).

Your point was that custom wheels have a significant advantage price wise. I was just pointing out that there are COTS wheels that are just as cheap.

Re: custom wheels
 

He has legitimate reasons for machining his own wheels. Power to him. I'd hardly call it a "list"


I'm trying to provide a set of reasons why teams may want to machine wheels. I don't think cost for the teams I've worked with would be a good reason because its nearly impossible to save cost on custom wheels.

Edit: Also I don't think I mention saving money as not a legitimate reason...

Re: custom wheels
 

If anything, what I'm seeing here is that, like everything on your robot, the efficiency and "worthwhileness" of custom wheels is something that is completely relative to your team. If you have all kinds of machining sponsors or a 3D printer, it might be worth it for your team. If you don't, not a big deal. It's how you want to allocate your resources (like anything in FIRST).

On another note, one of the benefits can be an integrated pulley, such as 3928 had on this year's robot. I can't tell you how nice that looked for a team that was struggling to use belts for the first time on our drive train this year.

Re: custom wheels
 

we build our own omni and mecanum wheels, we have CNC's, we find that they are a lot stronger and are lighter also. plus it is nice being able to tell a judge that you created your wheels

Re: custom wheels
 

Actually we used the white wheels from the KoP but we used duct tape to change it's atributes (it looses a lot of traction but gains speed). The thing I'm trying to say is that you don't need a 3D Printer or CNC to make your custom wheels you can modify any type of wheel. It's a lot cheaper but you have the risk that it may fail so, you need to check if it functions as you want.

Re: custom wheels
 

A 3d printer sound like a pretty expensive way of making wheels. How much did yours cost?

Re: custom wheels
 

The RepRap types of printers can start around $2K, depending on material source. $3K-$4K would get you a similar printer that's been modified/built by a company. Not sure what some of the top-of-the-line desktop models run.

Material typically runs about $15/lb. Might sound like a lot, but that's a lot of material for a lot of parts.

Re: custom wheels
 

Its sounds like you need a STL or a high end additive printer to get the strength necessary for wheels. Are 3d printers material runs about 30$ a pound and it isn't very good(Bits from Bytes). Are they lighter than the equivalent milled from aluminium?

Re: custom wheels
 

The one our school is looking at costs about $20k, I'm still crossing my fingers!

Re: custom wheels
 

If you don't have an STL file, you're not getting a printed wheel. You may mean SLS, a type of 3D printer.

But strength is a matter of material, and to some extent manufacturing method. I would say that a RepRap could produce a wheel that is strong enough for FRC, if the proper parameters were used in terms of fill amount and layers at the outside. RepRap-type printers' technical name is FDM (Fused Deposition Modeling), BTW.

Lighter? YES. Take a block of PLA or ABS. Now take a block of aluminum the same size. The plastic should be lighter (unless you're Wile E. Coyote).

You may have a printer type that uses a cartridge, or a powder (SLS draws on powder with a laser). That's much more expensive, in and of itself. If your material isn't very good, it may be expired--or you might need to look into changing your source.

Re: custom wheels
 

SLS my bad. Wouldn't you be able to use less material to make a aluminium wheel than a 3d printed one potentially making it lighter?

Re: custom wheels
 

It's possible... but unlikely.

Let's say that you have 2 wheels. They're identical in form, but because one is plastic and one is aluminum, they will have different weights due to densities. Aluminum is 0.1 lb/cubic inch; ABS is 0.04 lb/cubic inch. Let's say that both wheels have about 6 cubic inches (that would be a solid 4" wheel, 1" wide, with half its material removed somehow). 0.6 lb for aluminum, 0.24 lb for plastic.

Now, ABS's strength is about half that of aluminum, give or take a bit. So, you beef up the ABS wheel a bit--say you add back 3 cubic inches (which, for a wheel, is probably all you need). Still only at 0.36 lb. Adding back the entire material gives 0.48 lb, still less than the aluminum--I've been assuming that the aluminum wheel is strong enough this whole time.

BUT! 3D printing allows you to build stuff hollow, or with support structure inside--and much of the stress is carried in the outside of whatever you're working with. So you could actually build a pretty strong wheel out of ABS, without simply adding material willy-nilly, and be pretty light into the bargain.

Re: custom wheels
 

What are COT wheels? My school has a makerbot would that be suitable?

Re: custom wheels
 

COTS parts are bought and unmodified items. COTS wheels are any wheels that you buy, so colsons, AM wheels, and Vex wheels all fall into this category.

Re: custom wheels
 

COTS = Commercial Off The Shelf

Re: custom wheels
 

COTS wheels are Commercial Off The Shelf wheels. Translation: Buy them from a vendor, who may also be the manufacturer.

A Makerbot might be suitable for printing wheels. You'd have to get more specific on size and material, though--some of the smaller Makerbots might have trouble with, say, a 6" wheel.

Re: custom wheels
 

Thanks, Since were in Canada the plastic costs a quite a bit more especially with shipping.

Re: custom wheels
 

This is what we did this year, friend of mine made these up in CAD, he even included extra aluminum on the opposite side of the valve stem for counterbalance (we used the same rims on our shooter) Our sponsor machine shop turned out 8 of them. The spinners were actually the idea of our machinist. He had too much fun making them. :p
https://www.dropbox.com/s/14cvrmahmo...314_170616.mp4

Re: custom wheels
 

Actually a RepRap printer that would be able to make a pretty decent wheel is around $500- $1000 depending on where you buy the parts and on which model you buy. That is also an un-assembled version (I'm assuming that a robotics team would be able to put it together).

Re: custom wheels
 

118 has cool custom wheels. They 3D print the hubs, but then mold the tread themselves. They originally 3D printed the tread, then made the appropriate mold based off that.

Re: custom wheels
 

Almost. We actually mold our two piece hubs out of polyurethane plastic. The hub is designed to clamp our custom treads, which are molded from a concoction of polyurethane rubbers. A positive of each element is grown on the 3D printer and we make the molds by pouring silicon over the grown part. We can then make unlimited silicon molds from a single grown part.

Re: custom wheels
 

Last summer our team did some drive train development and on our robot this year we used a west coast drive with 4" Colson wheels:
http://www.robotmarketplace.com/products/BPDWC09.html

These were mounted on aluminum hex hubs:
http://wcproducts.net/wcp-00053/

We were absolutely thrilled with them. They have some big advantages:
- Being COTS components, they can be pre-purchased. Other than a quick sanity check to be sure you aren't making a huge mistake, the cost in build season time is essentially zero.
- They are very durable, and have very high traction.

Now, the costs:
- Each wheel costs a total of $20.99, so a set of six costs $125.94
- Each wheel weighs a total of .634 lb, so a set of six weighs 3.81 lb

With a baseline established, you have a basis for improvement.

Our team purchased a Makerbot Replicator just before the build season started, and used it to make things like hex shaft spacers, gearbox covers, and camera brackets. So far, strictly non-structural parts. We have been inspired by other teams to begin experimenting with making structural parts. We have started by looking at wheels, mostly because making your own wheels is cool, and that's what the off season is about, having fun and playing with cool things. We think it would be cool to have our team logo, or at least lettering, on the face of our wheels. So, we are playing a bit.

We started with this wheel.

Pretty cool looking, but nowhere to put a logo or lettering. Also, it could easily be just CNC machined. It doesn't take advantage of the nifty abilities of 3D printers.

Next, we did this one:

Can't machine this with a CNC machine. The spoke size and rim dimensions can be modified to make the wheel stronger, if testing shows that more strength is needed. But, the spokes are vulnerable and there still isn't anywhere to add a logo.

This is the latest wheel (printed last night):

Internally, this one has the same spokes as the previous wheel. On the inside and outside, there is a fairing surface that protects the spokes, adds some stiffness (and weight), and provides a surface on which to put a logo.

So let's do some comparisons to our baseline.
- Each wheel takes somewhere around 6 to 7 hours to print. This means that if they printed around the clock, a set of 6 wheels could be ready to go on the bot on Monday, after kickoff.
- Traction and durability are as yet untested, but based on the experiences of others, we should be able to make the hubs durable enough, provided that we do proper testing during the summer. Traction and durability of the treads will be on par with all the other wheels out there that require strip treads to be added.
- Cost: This can be looked at one of two ways. You can either include the cost of the machine and the plastic, or not. Because we already have purchased the machine and plastic, and the price of the plastic on the BOM is very low, I consider these parts to be free to the team. A 10 foot piece of 1" wide tread is going for $24 at AM right now, so we'll take $25 as the cost for all six wheels.
- Weight: The last wheel hub shown weighs .21 lb. Tread weighs .11 lb per foot (which is about the length needed for a 4" wheel), so take the weight of one wheel as .35 lb, and 2.1 lb for a set of 6.

So, those are the potential advantages and costs, from our teams perspective. One benefit not listed is that the team gets the experience of designing, testing, and building something cool. That's not worth nothing, even if it doesn't go on the robot.

What is needed to do the design?
- A 3D CAD package capable of generating stl files. Also helpful is some FEA capability, to help you make design decisions about geometry tradeoffs. Experienced design engineers can get very close to good designs by eyeballing things and using their judgement, but high school students don't have the experience yet. This is where working with your mentors will save you time.
- The initiative and enthusiasm to pursue the project.
- Access to a 3D printer, to build prototypes.
- Time and equipment to test the prototype wheels. We plan to torque test our wheels to failure, to see what their weak points are. We'll also torture test them on a robot to see if they will hold up to real world wear and tear. You want to break them to find their weak points now, not during competition.
- The willingness to take the results of all your hard work and publish it for the rest of the FIRST community to benefit from. Lawyering the rules aside, for you to fabricate something from a design you have developed before kickoff day, you have to publish the design for anyone else to use.

Re: custom wheels
 

Can't have a pulley come loose if its part of the wheel :p

We had zero issues with our drive modules and the belt running to the traction wheel, We managed to get them setup for a single CNC operation, and then slice off on the lathe. Very quick operations, worthwhile overall.

Re: custom wheels
 

Won't argue on cost, but I would suggest that the ability to put it together might run into some issues. I've built a couple RepRaps (actually, somewhat modified versions) and if I hadn't had a fully-functional one to reference, I don't think I could have done it. Mechanically, probably. Electrically, bring your own reference documentation.

Then I had the pleasure of showing a bunch of other teams how to build these printers. It took all day to get the mechanical part down; the electrical was being started.

I actually went in and rewrote the entire assembly instructions--CAD included--to make them easier to understand. (Couldn't do anything about the electrical, though.)


Now, that wheel comparison shown is pretty solid. Saving a pound and a hundred bucks, and possibly some time, could be huge in this competition. I do encourage that testing you're planning to do--break it, rebuild it, break it again, work all the bugs out, then build one without the fairing on one side for the judges to see.

Re: custom wheels
 

This year we designed some Custom 4" wheels that were made up of:
Two Custom Designed Rims That Were then Machined By Our Sponsor Chevron.
The Overall Idea was to be able to switch out The Fabric Quickly for when they would wear out. But it ended up that the thread we used didn't wear off that much!
We got a Roll Of Yellow Polyurethane and Got it Cut To Fit Our Rims which was a great thing!

Lots of People Would Come over to the pit and ask about our Wheel and look at it, so I decided to share some of the information here.

Images of the Rims: