Bike tires allowed?

We want to use 4 20" bicycle tires as our drivetrain. We couldn’t find much on wheels in the rules, so I am asking to make sure it is legal.

This is a picture of one of our wheels.

https://docs.google.com/open?id=0BxQuvG_kRGSbYzIyNTJjMjAtNGNkNy00ODUwLWFmMzUtOTFlOWE5NmNkZWQ1
^sorry it is a link to gdocs, my schools proxy is mean and doesn’t allow access to standard image sharing sites.

P.S. We want to put an empty water bottle on the robot to be a stationary block to stop basketballs. Is it allowed to put a plastic water bottle on the robot? =)

There are no rules prohibiting either. (If you really want to be certain, ask Q&A… but I think they’d tell you the same thing I just did.)

Just make sure that your drivetrain is geared for enough torque if you’re using that big of a wheel. A bigger wheel means that you’ll be moving faster for a given rotational speed, but it also means that you’ll possibly stall out your drivetrain and pop a breaker if you get into a shoving match.

I can’t find anything against them in the rules either, but I wouldn’t advice the use of pneumatic wheels simply because of the weight restrictions. Weight is always an obstacle, and pneumatic wheels weigh a lot. I did a quick Google search for 20" bicycle wheels, and found a “incredibly lightweight” bike that weighs 19.6 kilograms (about 44 lbs). True, that weight included the frame, but since you were planning on having 4 wheels (not 2) I would guess that the wheels alone would weigh at least 30 pounds–never mind the rest of your drive train! Also, I would be concerned about the strength of the tires–from match to match your robot goes under a lot of stress, and you don’t want to get a flat tire.

Hope this answers your question.

Keep in mind that while a larger wheel will potentially give you a higher top speed, a smaller wheel will will give you faster acceleration. As this years field is divided in half, I doubt that even the top speed of 8 inch wheels will be helpful. However massive bicycle wheels would shred through the bump =)

That’s actually a rather heavy bike for that size of wheel. The high-performance racing bikes don’t weigh any 44 lbs; my mountain bike, which isn’t high-performance, is much closer to the 20-30 lb range. It’s got larger wheels than that, too.

I’d be VERY surprised if 4 standard bike wheels came in over 10 lbs; I’d figure more in the 4-8 lb range.

With 20" tires, make sure you can get your bumpers securely fastened to your frame below the 10" limit. And getting smacked by a full weight short robot at the 5" level might hurt more than you think. Especially if you are both going full speed. I’m pretty sure I know who would “win” that collision.

coming from a cycling background, I will say this:

4 20" wheels could weigh that much if the lowest quality components were chosen. as in the junk found on the wannabe type junk At walmart.

if you went with better grade BMX comonents, the wheels would be lighter and stronger, as BMX wheels are meant to take a beating. stunt riders slam them into curbs all the time…

(its hard to see, but the rim is in 2 pieces… one split is held together with the rim sticker)

I would not reccomend using recumbent/folding bike wheels (skinnier rims), as they are light but not meant to take abuse. I have actually shattered aluminum road rims (700C, not 20" granted) on square curbs before:

http://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/45519_1542272726126_1514190571_31375058_3838731_n.jpg
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-ash2/40955_1542272886130_1514190571_31375059_392090_n.jpg

(as you might be able to see, the frame and fork were also damaged)

I was going about 15-20mph when I took a corner too hard… I weigh about 275lb.

IMHO, a robot getting slammed into the curb would not be that much different force wise.

Thundrio,
There is no restriction on wheel size. However, what will play into you decision is the need to have bumpers in the critical 2" to 10" above the flat floor. If that restriction meets with you design goals, the larger wheel may traverse the barrier.

My 700x23C (27in skinny racing-style rim) wheel with steel spokes weighs about 1kg. I assume a 20in one built much more robustly would weigh about the same, so weight shouldn’t be an issue.

That said, I’ve seen one team run bicycle wheels and they didn’t perform well. Things to consider
-Spokes are pretty delicate, and might get rammed by an opponent. Fixing spokes is a huge time-consuming pain.
-It’ll be really hard to turn in a 4WD configuration, unless you’re doing 2WD + caster.
-The torque problem - make sure you gear your motors waaaay down so they aren’t tripping breakers when you accelerate or get into a pushing match.

Another thing to take into consideration when considering using bicycle tires is their limmited contact with the ground. If you get into a shoving match with another robot, you will not only have to deal with the lack of torque caused by the large wheels, but the lack of traction between the ground and the wheel. We considered using bicycle tires for an offseason project, but the idea was scrapped due to problems with unpredictable fine control with the large wheels. This may come into play on the bonus bridges.

“… the idea was scrapped due to problems with unpredictable fine control with the large wheels.”

“The torque problem - make sure you gear your motors waaaay down so they aren’t tripping breakers when you accelerate or get into a pushing match.”

“Keep in mind that while a larger wheel will potentially give you a higher top speed, a smaller wheel will will give you faster acceleration.”

“Just make sure that your drivetrain is geared for enough torque if you’re using that big of a wheel.”

All true statements if you’re trying to drive the wheel from the center. Otherwise, not so much. Just sayin’.

Might have to break a few paradigm’s to make this omlette! Keep working it!

The contact patch can vary greatly depending on the exact tire and the air pressure vs load.

Contact patch is only part of the traction equation, the normal force is a lot of it and as you increase the contact patch you lower the PSI of the normal force.