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Calculate turning angle - 2 wheels car

  1. May 21, 2015 #1
    i am looking for a function for calculating the turning angle, using the difference between two wheels speed.

    i have a model car , with 2 engines and 2 wheels, without steering.

    thanks.
     
  2. jcsd
  3. May 21, 2015 #2

    Baluncore

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    Welcome to PF.
    What do you mean by turning angle? Maybe the radius r, of the curve measured from the midpoint of the car to the centre of the arc would be a better measure. If the car has a width w, with half width being h=w/2, then the radii of the two wheel tracks about the centre of the turn will be r–h and r+h. The relative speeds of the two wheels, u and v, will be proportional to the ratio of the radii.
    u/v = (r-h) / (r+h) which I think will give you something like r = h * (u+v) / (u-v)
    The sign of r should give you the direction of the turn.
     
  4. May 21, 2015 #3
    Thanks.
    I can't measure the radius r while the car is driving. I know the width W between both wheels and can control the velocities of the wheels.
    Is there opportunity to know the angle of the curve by these? For example, for turning 30 degrees what velocities will be needed in each wheel?
     
  5. May 21, 2015 #4

    Baluncore

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    You do not need to measure the radius. You specify the radius you require, then compute the ratio of the wheel speeds needed to achieve that radius.

    If you know the radius you can work out the distance you must travel to change direction by say 30°. Circumference = 2 Pi r,
    therefore the distance needed to turn 30° is d = 2 π r * 30 / 360.
     
  6. May 21, 2015 #5
    Are you programming a boe-bot?
     
  7. May 22, 2015 #6

    Baluncore

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    How do you measure or control the wheel position or rates. Shaft encoders, stepper motors?
     
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