Can we fill our wheels with water?

We were having a debate tonight on whether or not it is legal to fill pneumatic wheels with water. It would be a good way to add some weight to our robot (yes, I know :rolleyes:), but the catch is that it may violate R9. Do you all, especially current/former robot inspectors, believe “water wheels” to be legal?

No. Please Don’t. It isn’t worth the risk of soaking other robots or the field.

One of the QA answers said Slime (or leak sealant) was not allowed so I would presume water is probably out as well.

You may want to consider using radon gas to fill your pneumatic wheels, it’s about 8x heavier than air. :rolleyes:

Maybe just try to fill the tires with a little bit of concrete. Seems like a good idea to me. (Note the sarcasm I do not endorse concrete in tires nor water).

Try tungsten hexafluoride. It’s 11 times denser than air. Though please don’t use it with water together. It’ll release hydrofluoric acid which is bad.

Oh, and it’s toxic and corrosive. That might be a minus.

If you want to get real heavy I’d recommend pure lead wheels. They’re about 12,000 times heavier than air.

Downsides: it’s highly toxic and recognized as a carcinogen in CA.
Upsides: Basically everything else


It sounds like you might benefit from wheels made of quark-gluon plasma, which is over 30,000,000,000,000,000,000 times heavier than air. It would allow your robot to be an entire 1.5x10^-12 cubic centimeters big!

Disclaimer: If Radio is near wheels, might have comms issues.


So? That’s a small price to pay for the incredible benefits that come with having lead filled wheels.

In all seriousness though, probably not a great idea to fill your wheels with water. I can just imagine what would happen if you punctured a tire…

Why risk the heavy metal poisoning?

I recommend solid tungsten, it will be very easy to machine to fit inside the tire, and won’t be melted by the flames of the 10th defense.

Back on track:

There are far better alternatives to add robot weight, rather than filling pneumatic wheels with water. Instead of “useless” ballast, add “useful” ballast, strengthen that arm with some steel, change Aluminium hex out with steel hex etc.

What if you pulled the valve stems (the inside part, filled the tubes full of steel ball bearings, and then put the valve step cap back on. Would that work?

Just fill your wheels with depleted uranium - I mean, that’s what they use in the back of 747s as ballast.

To actually answer your question- In Ultimate Ascent a team in my area came to an event with the wheels on their frisbee shooter filled with water. The inspectors did not allow them to use those wheels due to the risk of the wheels leaking or spectacularly breaking and throwing water everywhere.

While I am not an inspector, I would imagine that this would not be allowed again this year. The defenses cause enough trauma to robots that the risk of the wheels breaking open is too high.

Your best bet would be to ask a Q&A question for an official judgement.

Realize it is not uncommon to fill off road equipment tires with water so this is as far fetched as is sounds. There is no rule specifically against this so it comes down to a judgement call to decide if it is properly contained. IE not likely to spill on the field. Same class as marbles, sand, BBs, and so on. Do keep in mind that this is coming from a team that never puts a robot on the field without a container full of lead & sulfuric acid.

As for as slime goes. We ran it in our Frisbee shooter flywheel to give it mass & balance. Got a controls award for the accuracy of the shooter at one regional. Good thing nobody ask Q&A is it was legal that year. :]

For the record, I was against this idea from the start. On a related note, 3 years ago we weighed down our robot by filling tube socks with metal bb’s and attaching them to the frame. I still can’t believe none of them ever tore.

Adding water plus an anti-freeze agent to heavy-equipment (and light-equipment too) tires makes perfect sense. I used a small farm tractor with water-ballasted wheels for many years when I was young.

However, zipping around an FRC field is a different matter.

If you want more mass, I recommend attaching solid weights at spots on the robot that move the robot’s center of gravity to a better place, in addition to adding mass.

I also recommend testing to find out whether adding mass helps more than it hurts.

Bottom line: Use the right tool for the right job. Your FRC bot isn’t a slow moving tractor or earthmover. Water is very unlikely to be the right tool for this job.

As long as they don’t go to a CA regional, it’s safe, right?

While tractors do this all the time, please do not put any fluids that could leak onto the field into your tires. There are easier and better ways to add weight to your robot. Plus, you will want that compressibility as you ram into defense and bounce around.