Re: 8" Pnumatic Wheels @ Andymark soldout
 

Those sneaky 4 inch wheels between your tires make me wonder whats going on over there :D

Re: 8" Pnumatic Wheels @ Andymark soldout
 

First, I may say I am a student, not an engineer or professional whatever. I do not have lots of years of industry experience, but physics was my favorite class.
I actually don't have any dislike for the pneumatic tires, and we considered the pros and cons of them plenty. But I'm not bummed that we can't get them, and that was just the easy way to rule them out for our team.

For the sake it, here:
Ease of use: Solid tires are easier to use for two reasons. Dropped center designs are very straightforward with solid wheels, and I have heard that sometimes you need a greater drop with pneumatic ones. I do not have experience with this, nor does anyone on my team, so we would rather not take a chance at having to fuss around with that. The other reason is managing the air pressure of the wheels. This could be related to reason #1.

Shock absorption: Seems to be the greatest benefit of pneumatic wheels. That said, I don't see how the impact of crossing defenses is going to be any more violent than the full court ramming that robots survived in 2014. Therefore I believe that the electrical and mechanical parts of the robot should handle it just fine.

Traction: We are planning on using 2" wide VexPro traction wheels, which I expect to have comparable traction to the pneumatic ones. I would like to see some proper testing of this if anyone could point me to it.

Summary: It is fair to argue that pneumatic tires could be better. If you have them and are planning on using them, it will probably work out well for you. But if you can't get them, don't worry, I don't think it will leave you with a disadvantage on the field, so it is not worth the time and money to go running around trying to find them.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

2014's collisions were bumper-to-bumper impacts. The bumpers allow the kinetic energy to exchange a little bit slower than instantaneously, reducing the impulse experienced by the robot. In addition, the bumpers were usually mounted to the main frame of the robot, which can direct forces throughout the robot in a uniform way.

When crossing defenses, it is your wheels that take the brunt of that force. A pneumatic tire acts like the bumpers do and reduces the impulse delivered to the robot, namely the axle. A hard wheel will shunt the full impacting force all at once into a shear impulse against the axle and its bearings, which could shatter bearings, or shear the whole wheel off.

In our testing, we build a chain driven west coast drive using VexPro versablocks, and due to the specific configuration could only get 2 bolts to hold it clamped to the frame tube. We put VexPro traction wheels on it and sent it at the defenses. After just a few crossings at decent speeds the chains had all fallen off. The impacts of the wheels colliding with namely the Rock Wall had moved each versablock more than 1/8" closer to the center until the chains got too loose. Obviously this was a problem specific to our configuration but I would not expect such a thing to have happened with pneumatic wheels.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

I am confused about the concern about the "shortage." I certainly understand that Vex and AndyMark are the "go-to" retailers for a lot of FRC items, but there are a lot of other folks who sell things such as pneumatic tires... Before responding here, I simply did a search on Google and found four or five different places to purchase such tires.... I glanced at one and it seemed to have all the other hardware needed for them...

Besides, even if there were a world-wide shortage of them, there are other options... Tank treads have been discussed on CD and are certainly viable. And, yes, there are options besides the Rhinos from AndyMark... Even so, could you play with a hard rubber tire (such as 8" traction tires from AndyMark)? Sure.... Okay, the hard rubber would not compress quite as well as pneumatic tires and not "bounce" over some of the surfaces as cleanly, but they could be used to cross all the hazards just fine - though I wouldn't want to go quite as quickly as I would with the pneumatic tires....

If worst came to worst, create a robot with a little different focus... A robot, for instance, operating with mecanum, could go under the low bar; open the portcullis, sally port and drawbridge; and navigate the cheval de frise. Of course, you might have to construct a manipulator or two... A mecanum robot could be fast, agile and have a perfectly good shooter... It could also climb just fine.... So, you could have a short robot with a mecanum drive system that primarily cycles between your secret passage, under the low bar and shoots at the high goal. As secondary functions, focus on opening the more difficult defenses and make sure you can climb. If needed, you could also cycle to the neutral zone to pick up boulders.

Do I think mecanum wheels are ideal? No. In fact, they would be one of my least -preferred wheel options for this game. However, with a little creativity, you could have a very competitive robot with them - or quite a few different drive systems. Heck, it might even force you to find a niche in the game where nobody else really fits and gives your alliances a competitive edge....

I've only been in FRC for five years, so I certainly don't know "everything." However, one thing (of many) I have learned is that you can't afford to get too attached to any one idea. Sometimes, they just don't work out - supply, lack of engineering expertise, too much weight, not enough space, etc.. Sometimes, you just need to take a different course. It's part of the game.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

Just putting in my two cents, our team found them in stock from Amazon.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

I also ordered some 200x50 tires and the tube from Amazon without issue out of curiosity.

I also stopped by the local Tractor Supply and grabbed a 10" knobby tube tire from them: 4.10/3.50-4 which is a tubeless tire. I also grabbed the same size tube.

That 10" tire has just under a 4" opening in the center. 3" PVC couplings have just over a 4" external diameter. I wasn't able to press one into the tire stock even with some petroleum jelly to help. I was able to put the tube around the stock coupling. I put it on my MaxNC lathe, used a dial indicator to check the run out, and then turned it down ever so slightly on the external sides of my centering 3 jaw chuck (minding the internal taper of that coupling). Finished it with some light sanding. It can be made to fit now into the center of that tire and tube around it (minding the air fitting will need an opening). You can put a tube in a tubeless tire. Need a lip on it and something in the middle. Not sure frankly if this tubeless tire really needs that tube in it as it is pretty rigid on it's own and for such a light vehicle as this that might be enough.

Total weight of the tire and tube is: 2.4lbs
Total weight of the turned down coupling is: 0.43lbs
Wouldn't be surprised if the whole thing comes in at 4-5lbs per tire with a hub.

I don't much plan on building this out any further but I had a hard time finding a 10" spoked tire that someone could use for a donor rim. Will try the same trick with the 200x50 tire when it gets here. All the AndyMark tires I had are otherwise occupied.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

Now that's what I call "Drive it like you stole it"!

Re: 8" Pnumatic Wheels @ Andymark soldout
 

The student driving that has a promising career in Hollywood as a stunt driver. Fast and Furious 9 or 10?

Re: 8" Pnumatic Wheels @ Andymark soldout
 

We are trying the HF 8"wheels, we removed the steel hub and used the 4 screw holes to make our 3D printed hub concentric. Probably we will be machining the hubs with some better plastic.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

For what it's worth, the AndyMark 8" pneumatic hubs are back in stock now. We ordered them and then bought the wheels and tubes off Amazon. That should allow us to handle our business with minimal fuss. (Just make sure you buy tubes with right-angle connectors, per AndyMark.)

Re: 8" Pnumatic Wheels @ Andymark soldout
 

ALERT!
The AndyMark 8" hub assembly for the pneumatic wheels appears to be in stock! :yikes:

Re: 8" Pnumatic Wheels @ Andymark soldout
 

We just spent the last week building custom hubs and a drivetrain with these same wheels. Watch out for the bearings. They don't seem... adequate. We're looking for other options still.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

Yes, we removed the steel hub and the original bearings, they can't handle the range of RPM that we use in FRC... Thanks for the hint, anyway!

Re: 8" Pnumatic Wheels @ Andymark soldout
 

These look to be similar to the wheels at Harbor Freight, but at the Canadian Equivalent Princess Auto, for teams that are interested. http://www.princessauto.com/en/detai...ly/A-p8442410e. The unfortunate thing is they don't come with a bolt circle to adapt a hub, and like the Harbor Freight wheels, the tire (2.8 x 2.5-4, whatever that means) does not appear to be compatible with the AndyMark hubs (200x50), but I would love to confirm.

Re: 8" Pnumatic Wheels @ Andymark soldout
 

Would you mind me asking what you replaced them with? Does anything from AM fit these?