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Measuring power generated at the rear wheels of a dragster

  1. Feb 16, 2010 #1
    So I am Googling around trying to figure out how one would go about taking this measurement. I have learned the 'book way' of calculating the power generated by the engine/transmission system of a vehicle; but how does one go about physically measuring it?

    I am learning about different kinds of sensor/transducers in one of my classes and would like to be able to apply some of that knowledge. Would anyone care to discuss any methods that they have had any experience with?

    I was thinking that one could use a 'bench roller' of sorts (like when you get your car inspected) and one could measure the velocity of the roller that spins as the dragster's wheel spin. But I am sure there are other/better ways including ways to measure the power in real time as the vehicle is driving.

  2. jcsd
  3. Feb 16, 2010 #2
    Hint: power is force times velocity.

    Edit: forget that actually. Measuring the velocity accurately is not that great since all tires slip in the real world

    New Hint: power is torque times rpm
  4. Feb 16, 2010 #3
    Hey Cyrus,

    Thanks. That was one of the ideas that had crossed my mind. I was thinking of setting up some sensor/receiver pairs in the wheel wells and using them to measure the rotational frequency of the wheels. I just didn't know if there was a different approach that is common practice in the 'real world.' Generally, I think it might be better if I could somehow convert the power put down at the wheels directly into a voltage.

    I am not sure if there is a practical approach to his though. For some reason a strain gage transducer on the drive shaft keeps crossing my mind...but that might just be crazy talking again.
  5. Feb 17, 2010 #4
    Power is force times velocity, therefore you can measure the speed of the dragster (and find out it's weight) and you can easily figure out how much power goes from the engine into accelerating the vehicle. Of course, probably some power is used up in smearing the tires on the road (I don't know how much), so your answer wouldn't be the total power.

    You can measure the speed of the dragster using a radar gun or accelerometer...or even figure it out using the various sensors they have spaced out on the track. For obvious reasons, the dragster's "speedometer", if it even has one, is not a good indicator.
  6. Feb 17, 2010 #5

    Ranger Mike

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    There are various telometry packages available to measure velocity and distance. One variable is wheel spin that must be factored in.


    forget using a dragster as the test vehicle. the current state of the art dragsters are 7000 HP rockets. weight is just over 1200 pounds and no way will rollers accurately capture the HP. the excessive wheel spin really complicated HP measurement.
    the dragster " pilot' will feather the throttle as well so it is a major guess..

    BTW. I know of no dynometers in use that can measure the HP of these engines and the HP is estimated..
    add in aerodynamics for 300 MPH blast thru the 1/4 mile and HP is a guess..
  7. Feb 17, 2010 #6
    Google torque sensor.
  8. Feb 17, 2010 #7
    Nice. Torque transducers that measure reaction torque seems like a step in the right direction.
  9. Feb 18, 2010 #8

    Ranger Mike

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    why worry about measuring it..see traction control ...illegal in most racing series but...??
  10. Feb 18, 2010 #9
    I don't understand. Why are you worried about me worrying about measuring it?:smile:
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