converting force/pressure into voltage

[hentai]

Hi,
a friend of mine asked me if i knew a device that could measure the strenght of a punch. All of a sudden all kinds of hidraulic system and manometers came in my mind but i couldn't give him a satisfying answer. So can anyone shine some light over this matter?
Thx a bunch.

 

[Pommie]

Use a punch bag and two break beam sensors to work out it's velocity.

Mike.

 

[stevez]

What do you mean by "strength" - is it the velocity at moment of impact? There's probably more to it than that.

You might construct a target that is displaced by the punch. The target would have some mass that might represent something - a person's head maybe. You might then measure/record the position of the target at various moments - possibly at millisecond or smaller intervals.

 

[House0Fwax]

I seem to recall a similar thread recently. People suggested using a partially inflated airbag within the punchbag connected to a pressure sensor.

 

[hentai]

Hi thx for replies.
Well, how can i put it in words, by strenght i mean "how hard does a person hit", sry for this lousy definition. Measuring velocity of a punch bag as Mike sugested seems logical, for the speed of the bag must be proportional with the force applied. Recording positions of a target object seems trickier especially at choosing the time intervals.
House0Fwax thx for the reminder, i always forget to search first before i open a new thread . The pressure sensor solution seems simpler but I'm wondering if its as precise as measuring velocity.

 

[Nigel Goodwin]

House0Fwax thx for the reminder, i always forget to search first before i open a new thread . The pressure sensor solution seems simpler but I'm wondering if its as precise as measuring velocity.

I would imagine it's probably more accurate?, measuring the speed of displacement probably requires more accurate construction and punching accuracy as well.

 

[OutToLunch]

how about an accelerometer? that would give you the "a" part of F=ma.

or maybe you could measure the velocity of the punching bag and measure how long the fist was in contact with the punching bag.

impulse = mass of punching bag x velocity of bag (initial velocity =0)
then the force would be
F = impulse / time in contact with bag

or maybe not - it's been a long time since i took physics.

 

[hentai]

Measuring the contact time with the bag might be a pain... The pressure sensor seems the simplest solution, the accelerometer also but i reckon one could have a hard time finding it. At first i was thinking of one of those linear displacement transducer... with a coil and a moving core... and an system with a spring that resisted the force and the transducer measuring the amount of spring deformation. (i hope i used the right words )

 

[Roff]

A velocity sensor will no measure momentum (the mass times the velocity). Measuring velocity alone, you couldn't tell the difference between a feather and Muhammad Ali's fist! Peak pressure should give you a fairly good measure of momentum.

 

[hentai]

A velocity sensor will no measure momentum (the mass times the velocity)

i see but wouldn't the sensor's output be proportional with momentum?

 

[Roff]

i see but wouldn't the sensor's output be proportional with momentum?

Only if the mass is constant. If you are testing the punching ability of one person, then that will work. If you are testing a wimp against a heavyweight boxer, then it won't.

 

[hentai]

Only if the mass is constant. If you are testing the punching ability of one person, then that will work. If you are testing a wimp against a heavyweight boxer, then it won't.

I got the picture now... thx for the tip.

 

[stevez]

If you think of the fist as a simple hammer then figuring out what to measure is easy. Unfortunately the fist is connected to the arm, shoulder, etc - and it's my guess that someone skilled in boxing knows how to put all of that to work to deliver the most devastating of blows. I am not sure that peak pressure would tell the whole story - I think the measurement needs to capture something like displacement of a known mass against time. I would expect that boxing coaches have had experts study the mechanics of boxing and there may be published books or journal articles on the subject.

 

[Pommie]

If the exercise it to measure the knockout potential of the punch then a punch bag that was a similar weight to a human head with an accelerometer in it would (IMHO) be the best solution.

Mike.

 

[arunb]

You could use a load cell instead...

 

[hentai]

Load cell? Please give more details.