AM lists the diameter in the title of the product as 8", but says the nominal diameter is 7.65". However in the CAD it is actually 8".
Which one is it? Is the 7.65" when compressed?
It’s strange that the CAD wheels are 8" because they are actually 200 mm (~7.8") wheels. I measured one of ours today and it was about 7.7".
Could it be an 8" wheel at maximum pressure? I doubt it would expand that much, but that’s my only guess
To anyone considering using pneumatic wheels who hasn’t used them before, I can only say get them early and get them driving quickly.
A 6 wheel drive train with a standard drop won’t turn well when the tires are compressible so that all 6 are on the ground.
We’ve used these pneumatic tires before - they were the rear wheels on our “Speed Racer” way back in 2008. https://www.youtube.com/watch?v=sR1ChpV1pio
(Although there’s a better view of the tires in the preliminary build-season video: https://www.youtube.com/watch?v=EZzOX9PVQnQ )
They are smaller than 8" as mentioned on the AndyMark page. I don’t have one in front of me to measure, but I seem to recall checking that 7.65" figure before and finding it to be correct for a typically inflated tire.
For teams having used pneumatic tires before in a 6wd, what do you typically use as the drop for the center wheels?
I understand you can play around with tire pressures to adjust this as well, but I am curious about the drop that is initially designed in.
We’ve usually needed a far-bigger drop for Pneumatic tires… the fact that they compress under load and are usually very grippy require it.
Usually rigid-ish wheels need 1/8" of drop or less… expect 1/4" or more for pneumatic tires. Inflation pressure, robot weight, and I suspect 6WD vs 8WD will all impact turning dynamics. Honestly, I wouldn’t shy away from 3/8" of drop for pneumatics… I’d prefer to have it turn a little to freely and adjust pressure to minimize than have it hop and draw high current and need to adjust.
As a side-note, also expect shockingly low tire pressure for pneumatic tires… most of them have a huge contact patch (particularly when you have 6 or 8 wheels on the robot) and FRC robots aren’t all that heavy for the size of that contact patch. I’d say expect 10-15psi, but I could see the center wheel on a 6WD being a moderate bit higher. When the tire is off the robot it’ll feel very soft.
We pressured an 8" AM pneumatic tire to 35 psi yesterday. The measured diameter was about 7-7/8".
If anyone is considering pneumatic wheels for the shooter, just some second hand experience:
Under high speed they wobble badly (can be balanced) and expand.
We used this tire for our shooter in Ultimate Ascent. When spun fast with low inflation pressure the profile of the tire changes due to the forces exerted on it. It was easily 8" in diameter at our highest shooting speed.
I would not expect to see this at normal FRC drive speeds.
Would increasing the pressure in the center tire, while lowering the pressure in the outer wheels have a positive effect?
We found a very counter-intuitive fix to this. Basically, take a little strip of metal (~2 inches long) and attach it at one end to one of the bolt holes in the wheel. It’s a bit of a feelings game, but when you adjust the strip of metal the right way, you can eliminate a lot of the vibration.
In Ultimate Assent our full court Frisbee shooter used the AM pneumatic direct mounted to CIM. We balanced the by adding a extra nuts on the bolt opposite of the valve stem. It was spun at 3600 RPM for the full court shots.
A favor to ask for those in possession of the AM pneumatic wheels. Can you tell me what lettering/words there are on the sides of the tires? Thanks
Thanks for this info, it’s good to hear from someone with experience :D. Considering that the KOP drivebase kind of locks you in to a 1/8" center drop, do you have any recommendations to mitigate this? I don’t really see a way to increase the drop with the holes currently in the side plates, but 1/8" sounds like it would have serious issues turning…
I saw a bot in 2012 using pneumatic wheels with about an 1/8th inch drop and they used duct tape over the front set of wheels to help it turn.
For the Team [Redacted] Ri3D robot we used the pneumatic wheel kit provided to us by AndyMark and do not have any problems turning. Note however that the robot is very light (sorry haven’t weighed it yet) and we assembled it using the belts included in the AM14U3 chassis kit that are for the “square” configuration and did not use the belts that come with the pneumatic wheel kit that are designed for a longer configuration. I believe that is what 'Snow Problem did with their AM14U3 and pneumatic wheel kit.
Unfortunately we don’t have any video up at this point of the robot turning. I believe we will have some in our reveal video which should post today.