Molding/Casting Custom Compliant and Solid Wheels

Technical
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#1

Ever since I started FRC, the question of whether we can manufacture our own wheels has always been in my mind. After seeing that many Turkish teams use duct tape wrapped pipes as intake and shooter wheels, I started to wonder more about the answer to this question. By making the wheels as cost-effective as possible, I aim to ensure that most Turkish teams have a better build and competition season.

Do you think it is possible to produce compliant and solid wheels ready to compete with a small workshop? If there are those who have done it before, what are the rubber suggestions, and if there are those who do, are the 3d printed hubs durable enough or should I turn to other options? I’m looking forward to anyone’s thoughts on this topic.

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#2

Foam sheets actually make nice intake rollers… Look for EVA foam or things like foam floor tiles. We used about 6 discs - 3DP spacer - 6 discs - etc. Two 1/16" wires were run the long way through holes in the 3DP spacers and stabbed through the foam discs to give them some drive torque transmission ability.

#3

Possible? Yes. Teams have done it. For US based teams it’s less economically optimal. But that may may change.

I know 118 did custom wheels at some point too but I don’t have that thread.

#4

I aim to create an ecosystem that not only works with this season’s game piece, but can be used every season. So I believe it would be more beneficial if I could make wheels similar to Vex and Andymark’s wheels.

#5

Unless I find very cheap material, I don’t think my productions could be cheaper than the Vex and Andymark ones, but given the high customs and shipping charges Turkish teams pay, it may be worth a try.

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#6

https://lcamtuf.coredump.cx/gcnc/

If it’s a path you wanna go down - this may be of some interest to you.

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#7

We’ve made swerve drive wheels with this smooth-on.com/products/reoflex-60/

The students always enjoy the casting process, but probably not worth it if you can use something COTS.

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#8

It is 100% possible. 3005 has done this for a number of seasons for FRC and FTC. The other Switchback battlebots team members and I also made our own custom molded wheels for last season.

In both of those cases we 3d printed open-topped molds, put in a hub/core, and poured liquid resin around the core. The cores could be 3d printed (Markforged Onyx is great for this) or made from metal.

The Smooth-On VytaFlex line of products is our go-to. The number after the name of the product is the durometer (e.g. VytaFlex 60 is ~60A durometer). I have no idea what the availability is for that outside of the US but you can probably find at least an equivalent product in your area.

The VytaFlex is a urethane compound and it only goes up to about 60A so if you need something harder you have to go with a different line and they’re typically harder to work with (tighter temperature requirements, need vacuum degassing, longer cure times, curing at elevated temperatures, etc. etc. all depends on what you get).

For that reason we typically have only molded intake wheels and stuff for the mechanisms and not drivetrain wheels.

That being said, last year 3005 ran a custom swerve module with custom wheels with 3d printed tread. I can’t exactly say I recommend it (buying a wheel is a far better use of resources if you can make it happen), but it’s possible. I think we ended up with 82A durometer which was super good for our drivetrain.

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#9

Do you have any photo of the finished product? Also, isn’t 60a durometer soft for a drive wheel and what material did you use for the hub?

#10

Linking in some past experiments.
TLDR: custom manufactured tread/overmolding wasn’t worth it. Custom wheel itself seems to be reasonable and we have done it for several years since. There is a heck of a lot that goes into roughtop laminate… All are not even close to being created equal.

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#11

I saw your teams swerve modules and i am amazed with them. I also got a photo at champs :smiley: . Thanks for all the advise, I will look for a similar product in my area to test it. Also, majority of the Turkish teams are using Andymark HiGrip wheels from the kit of parts to do the tough work, i should first focus on the soft wheels.

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#12

If you have 3D printing capability, you can also try printing things like small compliant wheel in TPU filament. TPU (thermoplastic polyurethane) is flexible enough that this may be an option that will work and you might be able to find a domestic source for it in Turkey.

#13

I already tried 3d printing intake wheels with regular TPU filament. However, they did not work. Their surface was not grippy enough to hold the game piece. I believe that overall durometer of the wheel is low but the surface is hard so that it is not grippy. Maybe it was because of the design of the wheel but i couldn’t get any good result.

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#14

1114 used to use a simlar product (Brush-On™ Series, Brushable Polyurethane Rubber | Smooth-On, Inc.) to make intake rollers from 2011 to 2014. We’d paint this on some lightweight vacuum pipe and suddenly you had a surprisingly effective roller.

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#15

To be fair this is extremely game-specific. The cargo this year is one of, if not the, most slippery game piece(s) we’ve ever had. There are plenty of gamepieces that printed TPU works fine on. I wouldn’t rule this out for future gamepieces.

#16

We used a reuseable 3dp outer mold with a 3dp inner hub. The top cup of the inner hub is cut away after castings. I couldn’t find any pictures of the process quickly. A small vacuum pot is helpful to get fine detail, but not entirely necessary. We could never get the cast material to adhere to either AL or onyx hubs. You need deep grooves to keep the tread on. I probably could get better pictures next time I’m at the build space.

The durometer seemed about right for a swerve wheel. I think we would replace once per regional.

wheel hub example

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#17

I totally agree with you but since I am trying to replicate the flex wheels, tpu seems like not a good option.

#18

Yeah, I hadn’t tried TPU for anything that needed a grip. Would sanding the grip surface help? That might break up the hard “shell” of the printed material and give it more of the grip you’d expect from polyurethane. Just a thought, as this is also something I haven’t tried myself.

#19

In 2020 we experimented with printing compliant wheels out of TPU. They held up surprisingly well and were decently reliable.
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We tried a number of different geometries, thicknesses, surface finishes, etc.

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Eventually we settled on this wheel, which had an HDPE insert to help preserve the hex bore.

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(I don’t have a picture of the assembled wheel with the insert, I’ll have to get one next time I’m in the shop)

As far as I remember, it never made it into an official robot, but we used them for prototyping in the past few seasons. The bottom line for us is printing the wheels is more trouble than it’s worth when we can buy them for relatively cheap (still more expensive than they would be in the US, but manageable if we’re already ordering a large shipment). But it was a fun project and a good proof of concept.

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#20

I’m curious how a wheel with a texture similar to the technique used here would work out. Obviously smaller loops, but I wonder how that would affect the grip of the wheel (and what the durability would look like too).