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What causes wheel to go in straight motion?

  1. Mar 17, 2005 #1

    What is the simple principle that governs cars with 3 wheels going forward?
    What are the specifications for the front wheel and the back 2 wheels? Do they have to have a specific ratio? Or something else? Please advice.
  2. jcsd
  3. Mar 19, 2005 #2
    It's quite simple, actually.

    It's all about the friction. Rubber, which is commonly used for tires has a very high coefficient of static friction against most materials, so if you apply the brakes, it basically goes nowhere.

    Because of its cylinder-like shape it can only roll easily in two directions - back and forth. This restricts the wheel to going in two directions only. Turn the wheel and/or apply rolling torque to make the vehicle go in the desired direction at the desired acceleration.
  4. Mar 19, 2005 #3
    a three wheel car is statically ballanced, meaning it doesnt have to do anything to be stationary and tip over. 2 wheeled machines like bikes need to be dynamically ballanced through motion.


  5. Mar 20, 2005 #4
    what kind of tires are best to produce straight motion?
  6. Mar 20, 2005 #5
    Tires can be made of virtually any solid and still produce straight line motion. Wheels only rotate about one axis and the alignment of the front and rear axis dictate the direction of vehicle motion. The rate at which a vehicle can turn is governed in part by tire composition but asking which is the best without giving any desired characterists is like asking what is the best vegetible. What size vehicle will this be? How fast will it go? What driving conditions do you expect? What safety margins do you want to use? What is your desired rate of straight-line acceleration? Tread design, tire composition, width, profile, radius--you have to look at all of these fetures to determine which will suit your needs the best.
  7. Mar 20, 2005 #6


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    The thing about cars is that their steering is calibrated after they roll off the production line. They are adjusted to drive straight. Like all other cars, this will eventuially drift out of true, and any car not perfectly tuned will not drive in a straight line without someone at the wheel.
  8. Mar 21, 2005 #7


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    Cars are inherrently stable: the axis of stering is in front of the axis of rotation (think, a castor on a gocery store cart), which causes the wheels to "want" to straighten out. That's why when you let go of the steering wheel, it turns to center. As long as the two front wheels are aligned with each other, the car will be inherrently stable and drive straight.

    Tires have nothing to do with it, as long as they are identical from side to side.
    Last edited: Mar 21, 2005
  9. Mar 21, 2005 #8
    so how can i make my autonomous small car go in straight direction? It has a wheel in the front, and 2 wheels in the back.
  10. Mar 21, 2005 #9
    Well, you can start by not turning the wheels. I don't understand your problem. What are you doing to not make your car go straight? Are you turning the wheels? Did you make sure the wheels were alighed? Do you have a weight distribution problem?
  11. Mar 21, 2005 #10


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    PrudensOptimus - the terms to use here would be "true" or "runout" to describe some of the problems.

    One tire is probably bigger, out of round and oblong shaped, and/or the axle is bent.

    This would make the vehicle tend to turn one direction and hop up and down.

    Replace the tires and axles or at the very least swap the side they are mounted on. Does the problem change at all?
  12. Mar 22, 2005 #11
    What are benefits of bigger wheels and smaller wheels?
  13. Mar 23, 2005 #12


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    No benefit to either.

    Have you tried swapping/replacing the parts in question to see if the problem is resolved?
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