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Unread 20-02-2011, 12:43
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Wheel base and Pneumatic tires

This year, we decided to go with some COTS pneumatic wheels to give us an extreme amount of traction. However, we are having some difficulty with turning (as you might guess). I believe the design of the robot is solid, we are just missing something in the execution. In low gear (about 3.5ft/sec) the robot turns perfectly. In high gear (about 13.5 ft/sec) the robot turns decently, occasionaly it trips a breaker, most high gear turns need to be made as part of a fluid motion with driving forwards.
Here is what we have:
8 wheel drive with these: http://www.grainger.com/Grainger/ERW...PE1?Pid=search
The two (per side) center wheels are dropped 1/4 inch
The turning base is 24 inches wide from center to center of the wheels, and it is 13.5 inches in length from center to center.

For those that have experience with pneumatic wheels, I am looking to what types of modifications will increase handling. Right now, all i can think of is switching out wheels and air pressure. On the air pressure note: I am having a hard time finding a pump with a gauge that will read in the 20-35psi range.
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Unread 20-02-2011, 13:19
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Re: Wheel base and Pneumatic tires

You could try programming an automatic transmission that drops into low as soon as you get to those low speed turns. Other than that, an air pressure increase seems like it would help. I can tell you right now though, we have had a fantastic traction experience with the roughtop plaction wheels from AndyMark, and they are a lot more predictable.
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Unread 20-02-2011, 13:21
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Re: Wheel base and Pneumatic tires

You may want to put lower-traction wheels on one or both ends. That helped a 6WD deal with turning issues.
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Unread 21-02-2011, 18:33
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Re: Wheel base and Pneumatic tires

Quote:
Originally Posted by EricH View Post
You may want to put lower-traction wheels on one or both ends. That helped a 6WD deal with turning issues.
Our bot was back side heavy with the 6 wheel configuration (it worked fine on concrete, but carpet was a killer). We could not turn during the scrimmage. So we replaced the back wheels with the smooth plastic ones, it was a thing of beauty.
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Unread 20-02-2011, 13:41
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Re: Wheel base and Pneumatic tires

Inflate the center wheels more - make sure they are as much as possible so they don't compress too much.

a 6WD might have turning issues, but a properly inflated 8wd shouldn't.
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Unread 20-02-2011, 18:36
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Re: Wheel base and Pneumatic tires

higher end bicycle pumps will give you an accurate reading in the 20-35psi range (I used to be a bike tech) make sure you get one with a schrader valve (car tire style) as many road bike specific ones are presta valve only (the long skinny one with the screw top).

maybe lower psi on the middle wheels and raise the psi on the outer wheels? (also lower the middle wheel axle a bit more)
lowering psi allows more surface contact thus traction. no offense to the other suggestions but increasing the psi in the middle will do you little good (except lowering the center wheel, but its much more practical to adjust the fixed axle position)

Last edited by WileyB-J : 20-02-2011 at 23:10. Reason: clarifacation
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Unread 21-02-2011, 13:25
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Re: Wheel base and Pneumatic tires

You may find the following whitepapers helpful. http://www.chiefdelphi.com/media/papers/1443 http://www.chiefdelphi.com/media/papers/1917
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Unread 21-02-2011, 14:12
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Re: Wheel base and Pneumatic tires

Thank you very much everyone, it was air pressure. Works great now that we have some more pressure in the tires.
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