AM Pneumatic Wheel Diameter?
 

I know, I'm surprised I'm asking this question too. Nevertheless, I need the diameter of a stock AM pneumatic wheel. Preferably inflated to 35psi or so. See, we only had the 6, and they're all in the bag with the robot....

Warning: Anyone who tells me it's 8" and links the AM spec page or CAD file risks being laughed out of the thread. That 8" diameter figure on the spec page is a transparent lie meant to cloud the minds of simple draftmens that think 2x4's really are.

Context: We're looking at swapping in either 6" or 8" IFI or performance wheels to get rid of the hilarious bounciness of our foolish 6-wheel pneumatic drivetrain. (Yes, we tried lowering the pressure in the outside tires and a few other things besides.) We need to know how much extra height we're going to get over the current wheels, as that starts pushing bumpers and things towards limits.

Re: AM Pneumatic Wheel Diameter?
 

We measured ours at 7 5/8" not supporting any weight... quite a disappointment.

Re: AM Pneumatic Wheel Diameter?
 

Ours are something like 7 3/8" when inflated to listed max pressure.

Re: AM Pneumatic Wheel Diameter?
 

Colsons are the answer to all problems

Re: AM Pneumatic Wheel Diameter?
 

The tires are actually 200mmx50mm and that should be at max size so you can figure closer to 7.5"

We had the same problem and swapped ours with 6" KOP wheels and are more than happy with the results. They have great traction, especially on the bridge, and are also showing amazing wear on our practice robot with many hours of use on them.

Re: AM Pneumatic Wheel Diameter?
 

+1. I wish there was a like button.

Re: AM Pneumatic Wheel Diameter?
 

See, I might believe you if I had the 4 extra pounds a Colson setup was gonna cost me, AM's 375 bearing hubs were back in stock, and my team had a load of time on our hands for the machining to turn a Colson wheel into something driveable. That, and I'd need to know the actual OD of those Colson wheels to know how they'd impact our height issues.

Sadly, I have none of these things. Nor have you provided me any useful information. So I fail to grasp the utility of your suggestion.

Next!

See, I knew that, but 200/25.4 = 7.874. Clearly there is a magic fudge factor involved here that no-one has told me about. It's like 2x4s all over again. I still remember the screams...

Re: AM Pneumatic Wheel Diameter?
 

Do you know how to search for information on the internet? Maybe a quick look at colsons website would reveal wheels in sizes from 1.625" to 8" diameter and widths from 7/8" to 2".

Searching just a pinch further would reveal a hub that will do exactly what you seem to need without requiring any machining. http://wcproducts.net/wcp-00052/

Even a pinch more searching....granted not much more would reveal that the weight difference between pneumatic wheels and colsons would be very close to negligible as well.

Re: AM Pneumatic Wheel Diameter?
 

Is there a need for the sarcastic response? Sorry for singling you out, but yeah, seriously people what's with all the rude behavior on here lately, we are better than this. And I agree with Kevin, you didn't provide us with any useful information; I don't see how the "colson's are the answer to all problems" added anything to this.

I apologize for the frustrated response.

Re: AM Pneumatic Wheel Diameter?
 

The answer was, I think, given: 7 5/8" from one team, 7 3/8" from another. If you allow for differing measuring methods, it sounds like 7 1/2" is a reasonable estimate.

I remember a similar issue with McMaster pneumatic wheels on 330's 2006 robot (6WD drop center, 6" wheels). It was fixed by replacing only one pair of wheels (the front pair, which was the least weight-bearing of the pairs) with the KOP wheels for that year, 6" Skyways (I want to say the tread was ground down first). For this situation, I'd say go with a 6" and gear and space it up and down appropriately. For some reason, I seem to recall that solid wheels get closer to nominal size than pneumatic ones.

Re: AM Pneumatic Wheel Diameter?
 

We measured the ones we ordered from AM to be 7.75", inflated to 35psi, iirc.

This is a lot of variance in the diameter of these wheels. It's a shame that these aren't more consistent because these wheels would be very good for this game, especially traversing the barrier.

Re: AM Pneumatic Wheel Diameter?
 

I will refer you to my original post, in which I am searching for hard data, because AM's website lists an inaccurate diameter for 8" diameter wheels. I assumed the implication that I'm not trusting websites at the moment was obvious. I do apologize and will state things more plainly next time for you.

Also, my google-fu indicates an 8"x1.5" sprocket & bearing ready Colson weighs in at 28 oz. Based on AM's weight specs (which I trust a bit more than the size) a sprocket & bearing ready AM pneumatic weighs in at 18 oz. So alright, it only costs me 3.75 lbs. This still doesn't help me.
EDIT: On the other hand, you're coming to Lone Star... So bring me a bag of six 8" Colsons ready to go and prove me wrong. I dare ya. ;)


EricH,
Some of my compatriots have suggested similar solutions, which is why I'm hunting up data on wheel sizes. Another mentor swears he measured them at 7.75", I measured one at Bayou at 7.5". To my horror, we're probably both right. At any rate, we're down to considering opportunity costs of our different options. We're running in a kit frame, so if I could just swap in 8" wheels on the front, life would be bliss. Or 8" wheels on front and back. I readily admit I like the grip those pneumatics have on carpet and bridge, and if they were actually 200mm, I'd go ahead with no worries. But if they're 7.5", then I'm obviously hosed. I'd much rather swap all the wheels and get back to a known solution than swap a pair, curse my luck, swap another pair....

Yes, 6" wheels with appropriate gearing and spacing could work, but that's even more time than a drop-in 8" replacement. Plus, our CG it biased somewhat back normally, but shifts more forward with the wedge down, and will shift radically forward if we ever get a robot on top of us.

All in all, I'm gunshy facing our second and last regional. I know we can get a standard 6WD running right. I don't have enough info on the actual size of our pneumatics to make me confident in a half-way approach. Yes, not knowing the actual size of the wheels on your robot is silly, but it was a really long regional, and it didn't matter outside this context.