As a part of some over the summer Creo training, me, some of my team members and a few members of another team are designing a mobile t-shirt cannon to be used at school events and other such demonstrations. We know that we want it to be able to drive outside on a variety of terrains (grass, asphalt, track, etc) so we decided it would be best to use pneumatic wheels for the drive base. I have two questions; one about pneumatic wheels, and another about our decision in general.
I was hoping to use 6" pneumatic wheels for spacing reasons however I can’t tell if they are sold by AndyMark. I found the 6" hubs for a pneumatic wheel here but the only inner tube and tire I can seem to find were as a part of FIRST Choice and is no longer listed on the website. As far as anyone knows, does AndyMark still sell a tire and inner tube that fits the 6"hub? I have seen other people’s suggestions on 6" pneumatic wheels from other suppliers for shooters in this thread but, if they are available through AndyMark, I would prefer to use those since that would require minimal modification of the wheels for the drive configuration we plan to use (6 wheel rocker running 1 live axle and 2 dead axles each side).
Do we really even need to use pneumatic wheels? We wanted to use wheels that were fairly durable that could go over any terrain one might encounter on a baseball or football field without the tread getting too torn up in the process. We chose the pneumatic wheels partly because of the cool factor (it is, after all, a demo bot ) and partly because they should give enough to kind of even out the ride as the robot goes over any bumps it may encounter. Would other wheels such as the AndyMark Plaction wheels or some kind of rubber treaded wheels provide the same performance?
Pneumatic wheels are nice, as they tend to be wide and don’t damage turf so much. You can also deflate them for even softer tires, and they hold up well on pavement.
I recommend you think much larger pneumatic wheels, like the size they use on a wheelbarrow. Harbor Freight sells these for about $6, including the hub with a 3/4" bearing installed. And a whole lot cheaper than AndyMark (not that I don’t just love those guys!)
The bolts holding the hub together can be removed, allowing you to bolt on an adapter if you wanted to drive the wheel with a chain or belt for example.
The 6" pnumatic wheels from mcmaster-carr fit the AM hubs perfectly, we used them on our shooter with no mods.
If you’re looking for an off the shelf solution from AndyMark I would go with their 8" wheels.
I would not go with the 10" wheels with a standard kit bot chassis, 1310 used them in 2012 and because of their size they could only feasibly fit 4. It was the worst drive train ever, nearly tipping itself if it ever did a full turn(more of a problem with wheel config, than the wheels themselves). If you can make a monstrous custom chassis these wheels will work.
We used the former with the McMaster-Carr 6" tire for our shooter and modified it to take a hex shaft. We pitched the weighty steel hub that comes with it. We also got rid of the inner tube (and the balance problems that went with it) and stuffed the tire with pool noodle.
Yes, it fits the 6" pneumatic plastic hub from AndyMark.
We lathed some excess off of ours to fit it into our shooter, I think the excess if for sprocket spacing. It lathes beautifully. Like 1334 we also scrapped the steel rims and inner tube, no pool noodle though. For a drive train I am sure you would want an inner tube.
Just a word of warning, the grey non marking wheels are just the black rubber wheels with a thin non marking layer on it, we noticed it starting to get rough after one shooter practice session. I am sure they would get torn up on concrete.
BTW last year if I recall correctly some teams didn’t use a dropped center, and instead just adjusted the air in their wheels to get the desired results.
Another option would be to use 6" Colson wheels and cut a tread pattern into each wheel, similar to what team 25 and 103 use. I’ve that they hold up to abuse well. West Coast Products make these handy little press fit hubs to make life a little easier. wcproducts.net/wcp-00052/
There is also a live axle version available.
Colsons do hold up to abuse, but if the robot is going over rough terrain it will transfer vibration to the chassis, and I am not sure how good it will be on grass or dirt. With the treads cut into them I am sure it will fling stuff all over the place as well. Great for concrete and indoor use though.
Thanks for all of the advise everyone, after consideration, we have decided to go ahead and use the 8" pneumatic wheels; if however, we do decide to use 6", at least I now know how to do it :). We will be posting pictures of this design once everything is finished, and hopefully some video of the cannon shooting.
Very good point, it didn’t occur to me that vibration would be a design factor but you are absolutely right.
Another good reason to stick with pneumatic wheels for this occasion.
Thanks for all of the advise everyone, after consideration, we have decided to go ahead and use the 8" pneumatic wheels;
if however, we do decide to use 6", at least I now know how to do it . We will be posting pictures of this design once everything is finished, and hopefully some video of the cannon shooting.
Glad to hear that you’ve come to a decision. One word of advice, make sure you lower your center wheel more than an average 6WD.
We used the AndyMark 8" pneumatic wheels in '12 and made the mistake of only doing an 1/8th inch drop. Our maneuverability and turning were absolutely horrific.
Maybe someone else can chime in with the correct numbers, but I think I’ve read that you want at least a 1/4 inch drop on your center wheel.
Do you think that with the uneven wheel inflation mentioned in an earlier post (center wheel more inflated than outer) a 1/8" drop would work? Not that it’s too hard to change in the model, just curious
We tried that and still didn’t have a lot of success with our turning ability.
We eventually wrapped ducktape around a pair of our tires to decrease our traction, and that was enough to get us turning better.
Anyways, increase your drop for sure.
Also, get a pair of wheels to test with and check their compression at full PSI.
That ways, you’ve got some numbers to design with, instead of just going off of what others think is the proper drop.
Hope that helps!
One way to experiment with centre drop is to mount your axles to small plates bolted to the chassis rather than direct to the chassis. Make an over size hole in the chassis to allow for vertical axle movement and then make up plates with different amounts of drop on the same bolt pattern. These go over the holes through the chassis. It’s a good idea to label the plates with the amount of drop. You’ll need them in sets of 4 - two for each axle. It doesn’t have to be the centre axle that gets dropped. Raising one pair (either front or rear) of the outer axles does pretty much the same thing and can be easier - particularly if you’re using direct drive. We didn’t need them this past season put have made them in increments of 1/16 in the past.