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V. Wheels and treads / Traction
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Well, what can I say… With a drive train on your robot, it is probably a good idea to use wheels or treads on that drive train.
This year’s rule say that you can use skyway wheels, any amount/any size… And any length of chain/belt, and the timing belt ruling changed into “Belt - Any size, Any length for use with pulleys”. So, go crazy, put on however many wheels/threads you see fit. Just remember, you don’t necessary get more traction by using more wheels/treads, just that it’s easier on the carpet if you do use more.
http://www.chiefdelphi.com/forums/sh...&threadid=1724
http://www.chiefdelphi.com/forums/sh...&threadid=1808
You can also make your own wheel, as long as you are using legal material.
“We made our own wheels. We used 6" circular solid aluminum (available from SPI) and took out some weight with holes, and added a built-in hub and bearing.” -Jeff Waegelin
http://www.chiefdelphi.com/forums/sh...&threadid=2054
Speaking of using legal material, a lot of times people have left over stocks of material that’s listed on small parts catalog, and want to save money by using those stocks instead of ordering fresh new ones from small parts. Now, the rules aren’t really clear about this, so try to stay within the rules, and the spirit of the rules… Gracious Professionalism is KEY.
http://www.chiefdelphi.com/forums/sh...&threadid=1965
Traction
Traction is what make your drive train work. If your wheels have no traction at all, your robot will be sitting at the same place burning carpet. Traction is also a limiting factor of how strong your robot can push. It is very likely that your wheels start slipping before tripping circuit breakers or stalling motors. A lot of teams learn the lesson about traction the hard way from last year’s game… They used unmodified skyway wheelchair wheels, and that wasn’t enough traction to get their robot up the bridge. On the other hand, you don’t want too much traction, which will lead to stalling motors or damaging carpet… So you have to give it a lot of thoughts and experiment before you get it right.
“You really don't want unlimited traction, because it will lead to stalled motors & or damaged carpet. Neither of these are good things. If you don't worry about traction in your design, you will not be likely to realize the benefit of all that torque, but if your traction is too good, you'll find yourself tripping breakers and shredding carpet.” P.J. Baker
“Get a fish scale. Hook it to your robot parallel to the plane the center of your wheels are on. Increase power to motors until you loose traction… Why the scale? The force you should read should be equal to your coefficent of friction times your normal force (weight). F=uM.” -Jon Lawton
http://www.chiefdelphi.com/forums/sh...&threadid=1979
Another good way to measure friction
“It is easy to make a test rig to measure the coefficent of friction. glue a piece of the sample carpet to a board and cut a couple on equal sized squares of wood, and glue various samples of possible tread material on them. add some weight, a spring scale and measure away.” -Dr. Bot
http://www.chiefdelphi.com/forums/sh...&threadid=1969
Wheels
Some of you should rethink about using those wheelchair wheels that came with the kit as driving wheels. They weren’t designed to push 130 lbs robots across a carpeted field. Modify them for more traction, or use different wheels.
“Buying wheels, if they make high traction wheels great, but those wheel chair wheels are useless. That is, unless you cut them up.” -401 Mentor
“Last year our team used the wheelchair wheels. We used a sloldering iron with a "V" shaped tip to cut tread into the tires. We had excellent grip.” - Wayne Doenges
http://www.chiefdelphi.com/forums/sh...&threadid=2015
A lot of cool wheel advices toward the end this thread @
http://www.chiefdelphi.com/forums/sh...&threadid=1424
Wheels vs. treads…
There is a good debate between using wheels and using threads. Basically there are pros and cons for each side. Wheels: while they are really efficient and easy to apply, they don’t provide nearly as much traction and contact surface. Treads: while they provide a huge amount of traction, they are hard to maintain and develop. Take a look at this thread for that discussion… There also great advices/ideas for wheels and treads in that discussion.
“have you ever seen the Technokats (45) treads? they had the most efficient and fastest drive systems out there. those things could plow over anything they wanted to.” -David Kelly
“In general, I would say that treaded systems are more difficult to debug and maintain. #45 has made it work wonderfully for them, but I would advise that your 1st robot have a simple 4WD, tank steering setup. It will be easier to build and you'll have a lot more time to debug it.” -P.J. Baker
“The TechnoKats have awesome drives. Their method of doing tracks is very efficient --- FOR A TRACK. I disagree with any claims that they are as efficient as wheels.” -Joe J.
“For us we wanted alot of grip of course. So what we did was
wrap timing belts around the wheels wit the teeth side out and we had superior traction.” - Andrew Rudolph
http://www.chiefdelphi.com/forums/sh...&threadid=1424
http://www.chiefdelphi.com/forums/sh...&threadid=2109
Treads
As I said, treads are difficult to develop and maintain… A lot of teams have good and bad experience with using treads on the drive train. Take a look at the advices they have about setting up a tread system on your drive train @
http://www.chiefdelphi.com/forums/sh...&threadid=1805
About wheel hubs…
Small parts sell pre-made wheel hubs for the skyway wheelchair wheels that came with the kits. For those of you who are using those wheels, the wheel hub is a great solution to attaching sprockets onto the wheel. They are really reliable, and teams haven’t complain anything major about those hubs. Meanwhile, those of you who aren’t using wheelchair wheels, you will have to figure out a way to attach sprocket/gear next to the wheels. Shouldn’t be too hard since a lot of the other wheels from skyway have bolts in them already.
“If you look in your Zone Zeal rulebook you will find the hubs. They are located on the pages after the kit and additional parts sections. One bit of advice. When tightening the hubs onto the wheels, be careful not to over tighten some of the bolts. You WILL distort the wheels causing them to wobble.” -Wayne Doenges
http://www.chiefdelphi.com/forums/sh...&threadid=1777
http://www.chiefdelphi.com/forums/sh...&threadid=1950
Also, skyway seems to sell keyed wheel hubs. This should be useful for those of you who are driving wheels with a driven shaft, such as having a direction connection between motor output shaft and wheel. Although, another solution is to attach gears/sprockets next to the wheel, and use chain or gearbox to drive that wheel.
“Skyway (from the fax) looks like they make others hubs that have keyways. I don't know if you can swap hubs but you might be able to purchase other hub/wheels that would attach by design.” -iscrc2
http://www.chiefdelphi.com/forums/sh...&threadid=1948
About wonder wheels
Wonder wheels, also known as holonomic wheels or omni-wheels, are side slip wheels with very little side friction. The way they work is that people manufacture these wheels out of legal material, and insert little free spinning disks or rollers around the edge of the wheel. Resulting a wheel that push forward with the gap between each disks/rollers digging into the carpet, and side slip on the free spinning rollers/disks around the wheel. With wonder wheels as two of the wheels on your tank-drive, the drive train can spin and turn around smoother, because the drive train will be spinning around the center of the two normal wheels instead of the center of all four wheels. One disadvantage is that the wonder wheels side of your drive train can easily be pushed from the side by another robot.
“The setup we used last year provided a good deal of traction left/right IIRC as we didn't have all 4 wheel mounts as omni-wheels. Instead we had a 4 wheel drive differential system with 4 omni-wheels in front, and 2 wide wheels in the rear with really good traction. This let us have 4-wheel drive and a good turning radius.” -Patrik
“We thought about using the side-slip wheels this year but decided not to. The reason, there is no way to stop your robot from being pushed around from the side.” -Wayne Doenges
http://www.chiefdelphi.com/forums/sh...&threadid=1551
About Skyway Pneumatics Wheels model online…
“I just posted a model of the Skyway 9x2 pneumatic wheel (p/n SPEC92P) in the mechanical library if your interested.” -Ed Sparks
http://www.firstcadlibrary.com/
http://www.chiefdelphi.com/forums/sh...&threadid=2087