how can i measure speed of wheel?

Discussion in 'The Projects Forum' started by chubbron, Sep 27, 2012.

  1. chubbron

    Thread Starter New Member

    Sep 27, 2012
    hi, i have a new project which require me to analyze the dependence of tangential velocity to angular velocity between two different sizes of wheels. can anyone help me how can i measure and show the speed of the wheel? other than using sensors? or if using sensor is a good idea, brief me a simple one? and by the way, i will be using motors and some potentiometer to control the speed. i havent build this thing so i'd appreciate some ideas. thanks :)
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    I can't imagine any way to determine the speed of a wheel without using sensors of some sort...unless your eyes are well calibrated. :)

    My first thought is a hall effect sensor and a magnet located on the wheel. When the magnet passes the sensor, the sensor outputs a pulse. Then, you can count the pulses, which will give you speed in RPM. Or you can factor in the diameter of the wheel, and calculate the speed in linear terms.

    Or you could do it with a mirror on the wheel, and a light source and sensor on the same side of the wheel.

    Or you could do it with hole through the wheel, and a light source and sensor on opposite sides of the wheel.

    Or you could attach a flexible stick to the wheel, and have the flexible stick operate a lever switch on each revolution.

    Or ... well, you get the idea.
    Last edited: Sep 27, 2012
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  3. mlog


    Feb 11, 2012
    The simplest way is to use a ferrous gear and count the pulses as the gear teeth pass by the coil of a magnetic pickup.
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  4. wayneh


    Sep 9, 2010
    Why would this analysis ever be more than a paper exercise? This is standard geometry and physics.
  5. chubbron

    Thread Starter New Member

    Sep 27, 2012
    of course it is easy to do it the way you say it but, it's a semester project and we are required to show it, like build a system/gadget/machine that will show the dependency.
  6. DickCappels


    Aug 21, 2008
    You can use a stepper motor. If you know the change in angle per step, you can calculate the number of steps per second needed for a particular angular frequency.

    Your circuit would look like this: Pot =>variable frequency oscillator => stepper controller (two filp-flops) => stepper driver => stepper motor. A frequency meter measures the frequency of the oscillator to indicate the angular velocity. Its easy because its digital all the way up to the motor.
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    or you could use a small(toy) DC motor as a generator and read out voltage directly on a meter 'scaled' with appropriate number of RPM's A tiny friction wheel drives the genny and the voltmeter moves in real time.

    "It was called ANALOG technology when I was boy", cried the old cripple, as he waved his walking cane in a shaky, but menacing fashion.... :)
  8. wayneh


    Sep 9, 2010
    Ah, I see. That means that you must measure each independently, right? It's not enough to measure only RPM and, knowing the circumference, calculate tangential velocity the way a bike computer does. You actually need to measure tangential velocity?

    Spinning a genny as suggested would accomplish that. Again thinking of a bicycle, the traditional bottle dynamo is powered by the tire's tangential velocity.

    Some old turntables used to have alternating light/dark marks on their outer perimeters. You could tweak their speed by strobing these marks and adjusting speed until they stood still.
  9. Bernard


    Aug 7, 2008
    Do you have access to a frequency or events / unit time meter? If wheels are solid , a light-dark patern can be detected with a single ended photo reflective sensor- available from most old VCRs.
    What part of the world are you in?