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http://www.youtube.com/watch?v=39dXQ...e=channel_page

oh yea look at them wheels.

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I hope those wheels are a joke. If not then adding wheels does not increase traction. Traction is only influenced by the normal force and the coefficient of friction. Also it looks like the front wheels are unpowered which would decrease your total force you can apply as well. Basically. The amount of wheels doesn't matter this year, and all of the wheels should be powered for the maximum usage of available traction.

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but doesnt having less wheels work better? i think so because with less wheels you are distributing more wieght per wheel making the friction due to gravity greator. (not sure if its right though, just something me and a few other students were disscussing)

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This is partially right. If all of the wheels are driven then it doesn't matter. Each wheel will have less traction per wheel due to a lower normal force per wheel but the total traction will be the same as the more wheels will add up to the same value. Either way having 16 wheels does not improve traction at all and having unpowered wheels even with 16 wheels means this drivetrain will have less traction than a simple 4wd design.

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all the wheels are powered. That clip dosnt do justice to how well it preforms.

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At least all the wheels are powered. You are wasting a large bit of the weight budget with those wheels though.

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Are you using any sort of traction control or steering augmentation? If so, I'm going to have to rethink my plans...

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I'm sorry to burst your bubble... but more surface area will have next to no effect on the Glasliner surface. Do the math/physics you may want to think about saving all that weight for something else.

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Not at all arguing the physics of friction, but one thing that may change with the extra wheels is how the robot performs while turning. While with this robot, you will certainly not get any more friction when driving in a straight line, distributing the frictional force of the wheels around the robot means that when turning, the amount of torque that each wheel is supplying will be different as its distance to the axis of rotation, for both the linear and transverse friction of the wheels.

While I have not done any actual math, playing with vector diagrams a little yields this:


So it seems that not only are more wheels hurting your weight, they're actually decreasing your ability to turn.
Interesting; have your tried to do comparative testing with only four wheels? Or someone correct me if I'm wrong.

--Ryan

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Some of you missed the point of the video. Watch again and listen carefully to the video. First run is without traction control, second run is with traction control. Notice the obvious difference in traction and acceleration.

This obviously is a proto-type. Any team smart enough to pull off what they did know about wheel configuration.

Good job team 702.

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Another thing to condsider with multiple wheels. Unless each wheel is EXACTLY the same diameter, only the larger wheels will make contact with the floor. On carpeting this wouldn't make much of a difference, but since we are playing what is essentially a flat floor it should make a difference IMHO.

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We originally had ideas to utilize multiple wheels to increase traction but after review our physics a little realized that that would just further distribute weight and traction would remain the same.

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As much as I agree with the statement that "in the simplified theory of friction as taught in high school physics class, extra wheels should not increase traction", it is important to remember that the simple relationship between normal force and resultant force makes some assumptions that may or may not hold true in a practical environment.

For instance Formula One race cars evidently find that having a larger contact patch improves traction. This does not contradict the theory taught in high school physics, but does mean that some of the assumptions made in that theory are not valid in the race track environment.

For instance the "high school" theory assumes that neither surface deforms due to the normal force (remember that the regolith lies over top of carpet, and is a fairly thin material...), nor fails under the resultant force. Given the "white powder" produced by spinning wheels as reported on CD, there is definite surface failure during dynamic friction of highly loaded wheels. Perhaps this is less of an issue with lightly loaded wheels....

Perhaps they are on to something with this design, perhaps not. I suspect not, but if the team has tested multiple wheels and found them to be an improvement then they have my congratulations for not being bound by the assumptions of a simplfied theory.

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That's So Awesome.

How many wheels did you have in the back? 8? 10?

In theory more wheels will not increase traction but it will change how your robot handles with the traction thats given. So maybe having that super awesome wheel thing in the back is actually helping them turn with the trailer......