Tiny wheel

[asid61]

So I've seen teams use 4" wheels usually, and in some cases 3.25" wheels, but what stops teams from using wheels as small as 2" or 2.5"? Just out of curiosity.

I would think tread wear and not being able to sit closer to the ground due to 2x1 geometry would be the main reasons. However, I feel like you could reduce gearbox weight a little bit by using smaller reduction ratios.

[JohnFogarty]

Not being an expert in physics here, but if you go any smaller in wheel size I'm betting the wheels wouldn't support the weight of the robot.

I've never even seen FTC teams use smaller than 4" wheels really.

[orangemoore]

Originally Posted by JohnFogarty

I've never even seen FTC teams use smaller than 4" wheels really.

Do you mean 3 inches?

[cadandcookies]

Originally Posted by JohnFogarty

Not being an expert in physics here, but if you go any smaller in wheel size I'm betting the wheels wouldn't support the weight of the robot.

I've never even seen FTC teams use smaller than 4" wheels really.

I think that if you ran a solid aluminum cylinder you could probably support a robot. Heck, I'm willing to bet that it is physically possible to make a robot with 2" wheels. I believe 118 even used <2" omni wheels this year for their actuated system.

I think there are a couple of factors at play. One is definitely packaging-- standard FRC bolt patterns and interfaces don't necessarily fit on a 2" wheel. Then there's making sure you have enough ground clearance (most teams seem to have a clearance >1", more with games that have actual field obstacles), which means you are probably going to have to do a custom frame (good luck using the AM14U for this, or "normal" 1x2 tube). Ultimately there are a lot of interesting design challenges that might go into it (I might designing something with <2" wheels this summer to get a feel for this, actually).

The other is a lack of COTS parts-- the majority of teams don't spend the time or resources to machine their own frames, much less their own wheels. For them, there's little reason to move away from cheap and commonly available kit frame and wheel options.

There's also frankly not been a game that demanded "microwheels," or even really encouraged going outside of COTS components for wheels in recent years.

There's also a tradeoff for effort to design a custom solution versus the (relatively small) amount of weight saved.

[asid61]

Okay, I can see load being a problem. Colsons from Robot Shop, 2" diameter are rated at 75lbs. Could be okay depending on robot weight and how many spares you have. 2.5" wheels are rated for 140lbs, which is perfect.
Ground clearance this year was almost nonexistent, but yeah, in past years there's usually some kind of obstacle.

[Mike Marandola]

Kika Mana uses pretty small wheels for their swerve. I'm not sure exactly how small though.

[R.C.]

Originally Posted by Mike Marandola

Kika Mana uses pretty small wheels for their swerve. I'm not sure exactly how small though.

3.25" VersaWheel Dt's

[Mike Marandola]

Originally Posted by R.C.

3.25" VersaWheel Dt's

Ah, the tread pattern was worn off. They aren't too small then.

[Tyler2517]

Were designing a swerve with 2-3 inch wheels right now. It so much easier to get the gearing right. The drive Base is a bit larger, almost on par with west coast. You can definitely support a robot with a aluminum wheel that small. Obstacles could be a problem.

[fox46]

Just be sure that you bring spares if you are running wheels that small.

All your tread wear will be focussed to a smaller surface area of tread so a 2" wheel's tread will burn off twice as fast as a 4" wheel's and three times faster than a 6" wheel. After seeing photos of some post-competition racing slicks I would shy away from anything smaller than 4" and even then I would be worried.

[fox46]

You could of course mitigate the wear by going wider but then you're increasing size again.

[Rob Stehlik]

Originally Posted by fox46

Just be sure that you bring spares if you are running wheels that small.

All your tread wear will be focussed to a smaller surface area of tread so a 2" wheel's tread will burn off twice as fast as a 4" wheel's and three times faster than a 6" wheel. After seeing photos of some post-competition racing slicks I would shy away from anything smaller than 4" and even then I would be worried.

Agreed. Rapid tread wear is the main drawback with small wheels. We burned through three sets of 4" wheels last year, and I got tired of changing them (not trivial in a dead axle design).

[Joe Ross]

Originally Posted by Mike Marandola

Ah, the tread pattern was worn off. They aren't too small then.

They told me that they grind the tread off, purposefully.

[asid61]

Originally Posted by Joe Ross

They told me that they grind the tread off, purposefully.

Yeah, I heard that too.
Tread wear. With WCD it shouldn't be as bad to swap out wheels.

[Joey Milia]

The smallest wheels I've seen used were used on 973's swerve drive in 2012.

192 ran wheels just under 3.5in this year and will most likely be going with 3in for the offseason and next year. 3in is probably as small as we'd go for use on a WCD, might go smaller with a swerve drive though. Small wheels make a huge difference when trying to make the drive gearboxes small and light.