Topic: Impact Meter

[Huw]

Following on from Susan's thread. Does such a thing exist ? Has anyone seen one?

[gizmo]

Yes Huw, I've seen several. Although Moley calls them demonstration partners.  

[Huw]

Yes Huw, I've seen several. Although Moley calls them demonstration partners.  

As I found out several times (in the head) last week Gizmo   Some things never change eh!!!

Seriously is there no way of measuring, for example, how hard a boxer hits? It can't be THAT hard to build an impact meter  

[wani]

Ever been to Ffair Borth?

Either using strain guage or Differential Pressure (DP). Low cost systems can measure this accurately. They just require rigid fixing and calibration (zeroing) to relative atmosphere. These things can probably be picked up from EvilBay.

W

[Huw]

Either using strain guage or Differential Pressure (DP). Low cost systems can measure this accurately.

I was thinking that using piezoelectric chips would do the trick. I'll check out EvilBay.

H

[Moley]

When I was a Kid, I seem to remember a punch ball in Funfairs.
Put a Sixpenny piece in ..
The harder you hit it, the greater the rating you got. Something like Sailor then Stoker and all sorta things ending up with Steviedor. (A MYSTERY TO THIS DAY)

[Huw]

Stevedors = dock workers who unload ships.

Before machinery took over they would have been strong lads. Could it be them?

[GuyB]

Ever been to Ffair Borth?

Either using strain guage or Differential Pressure (DP). Low cost systems can measure this accurately. They just require rigid fixing and calibration (zeroing) to relative atmosphere. These things can probably be picked up from EvilBay.

W

There was a project in our department once called the 'knee trembler'.. it did rather well and I always thought the way it worked was cool.

Basically, the 'victim' stood on a metal plate that was suddenly dropped down an inch or two onto a firm base. Strain guages in the device measured the stresses in the plate and sent data to a digital oscilloscope. The D.O. thus produced a trace describing the oscillations taking place in the leg as a result of the drop. This could be used by doctors to identify and measure properties of the knee joint, and spot potential problems.

Sadly it never really took off.. something to do with patients with knee problems being reluctant to volunteer to be repeatedly dropped a couple of inches.

The Makiwara strain guage idea got me thinking.. you could do a similar thing for a karate punch. Someone like Gizmo would have a field day with the data. With that sort of feedback, you should be able to 'see' the effect of kime on the trace.

Damn.. I wish I was a proper lecturer (instead of just a mug who lets the university walk all over him).. I'd have a couple of students on this in no time.

[GuyB]

Either using strain guage or Differential Pressure (DP). Low cost systems can measure this accurately.

I was thinking that using piezoelectric chips would do the trick. I'll check out EvilBay.

H

I wonder if you could use a piezo-guitar pickup somehow? They're very sensitive and bond well to wood.

I've got a climac 'wall makiwara' on order at the moment.. I might have a go at 'modding' it when it 'eventually' gets here.

[Moley]

Huw:
Bring "THE BOARD" tonight.

[wani]

Yes, for 'calibration' purposes only.    

W

[GuyB]

Take a look at this..

http://polly.phys.msu.su/~zeld/oscill.html

It turns a PC (or laptop) into a digital oscilloscope by using a standard soundcard as an A2D converter.

Dunno how well it works.. but it might be possible to use this for looking at the impact dynamics of karate punches. Which would settle a LOT of arguments

[Huw]

I'm not sure if a soundcard would have enough bandwidth to cope with the range of measurements required. I reckon we'd need a device thgat could measure between say one kilo of force up to a thousand kilos or more.

The idea I had was to use a piezo electric transducer (like they use for measuring road traffic etc.) and to measure the current coming out of that. A guitar transducer is IMHO going to be too fragileto cope. If you can get a sensor that works in the right force range it *should* be pretty straight forward ... Not that I could build it of course !!  

Here's a question to all makiwara owners - how much travel or give should the electronic makiwara have? I'm guessing it would have to be wall mounted so some 'give' is essential.

[GuyB]

I'm not sure if a soundcard would have enough bandwidth to cope with the range of measurements required.

Eh?.. modern soundcards have MASSIVE bandwidth Huw, 10-15KHz at 16 bits! That gives them a time resolution of about .1 microseconds at least.. should be WAY more than enough to cope with the timings involved. A 16 bit A2D'll give you a sample resolution of 66,000 possible descreet values for the measurements.. I'm sure that'll do for our purposes.

I've been looking at sensors on the internet.. theres a massive variety of peizoelectric bending and compression sensors that could be used. A bending sensor mounted behind the 'pad' of the makiwara might be the best option.

Its then just a matter of building a variable gain small signal amplifier for callibration (an 8-pin chip and a few resistors) to interface the sensor to the soundcard and Bobs your mothers brother.

It'll take a bit of thought to work out how to interpret the traces in terms of improving technique (you might need to take the harmonic properties of the wood into consideration for one thing).. but at the very least you'd be able to get a feel for the peak impact power (peak of the trace) and even the speed of the punch (half width of the peak).

[Huw]

AH HA
OK. We were on different wavelenghts about how to go about this. I was thinking more stand alone consumer item while you where thinking more scientificly. OK lets go with yours first so we can see what lessons there are to be learnt.

I have a spare PC (or three) and sound card. Which sensors have you been looking at?