Measuring power generated at the rear wheels of a dragster

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Discussion Overview

The discussion revolves around methods for measuring the power generated at the rear wheels of a dragster. Participants explore various techniques, sensors, and theoretical considerations related to this measurement, including practical applications and challenges faced in real-world scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests using a 'bench roller' to measure the velocity of the wheels as a method to calculate power.
  • Another participant points out that power can be calculated as torque times RPM, although they later express doubts about measuring velocity accurately due to tire slip.
  • Some participants propose using sensor/receiver pairs in the wheel wells to measure the rotational frequency of the wheels, considering the conversion of power into voltage.
  • Concerns are raised about the complications of measuring power in high-performance dragsters due to factors like wheel spin and throttle control.
  • One participant mentions the use of radar guns or accelerometers to measure speed, while noting that the dragster's speedometer may not be reliable.
  • There is a mention of telemetry packages that can measure velocity and distance, but the challenges of wheel spin are acknowledged.
  • Some participants discuss the limitations of existing dynometers in accurately measuring horsepower for modern dragsters.
  • Torque sensors are suggested as a potential solution for measuring power more effectively.
  • A few participants question the necessity of measuring power, referencing traction control systems used in racing.

Areas of Agreement / Disagreement

Participants express a range of ideas and methods for measuring power, with no clear consensus on the best approach. There are differing opinions on the feasibility and accuracy of various techniques, and some participants challenge the need for measurement altogether.

Contextual Notes

Participants highlight limitations such as the impact of tire slip on measurements, the complexity of high horsepower dragsters, and the unreliability of certain measurement tools in extreme conditions.

Who May Find This Useful

This discussion may be useful for individuals interested in automotive engineering, drag racing technology, and measurement techniques in high-performance vehicles.

Saladsamurai
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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.

Thoughts?
 
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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
 
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.
 
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.
 
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..
 
Saladsamurai said:
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.

Google torque sensor.
 
Cyrus said:
Google torque sensor.

Nice. Torque transducers that measure reaction torque seems like a step in the right direction.
 
why worry about measuring it..see traction control ...illegal in most racing series but...??
 
Ranger Mike said:
why worry about measuring it..see traction control ...illegal in most racing series but...??

I don't understand. Why are you worried about me worrying about measuring it?:smile:
 

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