Homemade Forceplate for Gait Analysis

[hotponyshoes]

Hi all,

I am new here, studing equine motion.

 

I am looking to start using force plates (ground mounted) to asses weight transfer on a horse foot.

 

I am looking for the following information / ideas,

 

Sources and prices of existing systems suitable for my use..

Any information on a diy version?

 

Ideally the working of the system would be pc based. Using the sensors in the force plate as pixels they would show on a computer screen much like a thermal image. Ie, they could all be blue when no load is applied, red at full load and various other changes inbetween.

The computer would start to 'record a video' as the first one changed and that could then be replayed to show the weight distrubition moving over the plate.

No actuall data (speed or force etc) needs to be recorded, just a visual report of the weight transfer.

 

 

I am currently thinking of building some sort of force plate, the minimium size would be about 350mmx350mm.

The ideal size would be about 500mm x 6-700mm.

Ideally it would be under 1mm thick so I could simply lay it on the ground but I think this is unlikely!

 

My first idea is as follows:

 

Use QTC pills as the sensors.

They are very small, 3.5mmx3.5mmx1mm. That is about the only thing I know about them.

I am thinking that if it was possible to mount them to a thin plate (maybe machined nylon) I could use this as the base and the carrier for the cables.

If I am correct they change state from infinate resistance when no pressure is applied and progressavlly drop to 0 restance at full compression.

I presume they need 2 wires to them.

It may be possible to use some sort of flexible pcb to act as a common and then just run one wire to each pill.

This leads to it's own problems however, at 3.5mm square a 350mm plate would need 10,000 pills.

Although they are reasonable cheap individually that's still expensive. It also involves trying to connect 10k wires to something and being able to process that amount of information.

I could space the pill centers at 5mm which reduces the count to under 5k.

Any further than that and I thing I will drop to much detail.

 

Second idea is to use some sort of multi-layer flexible pcb.

If it was possible to make a 3 layer pcb, top layer having some sort of grid array with coordinates interfaces to some sort of reader, bottom layer the same, middle layer some sore of material that allowed the 2 outer layers to touch.

This would give a simple set of X&Y points read out when pressure was applied.

If I could make several of these plates and have the middle layers in varying density then one plate could react with little force and they could get progressivly stronger.

Say I made 3, put them all on top of one another, first one would light up green, second yellow, third red, or something?

 

Not really sure how the commercial systems work but if anyone has any info/links/ideas that would be great!

Thanks!!

[imatfaal]

Personally I have no clue but as soon as I read the above I was put in mind of the force measuring pedals that (if you are one of the madly rich types) can be bought for bicycles. These constantly measure the force being applied by each foot and store the information on the on board computer. You can search on Garmin Vector. They are seriously expensive (about 1000 quid a foot!) so you might want to speak to Garmin and see if they can tell you what is going on inside rather than buy a pair to take apart.

[John Cuthber]

My guess is that they use a bunch of these

http://en.wikipedia.org/wiki/Strain_gauge

 

What are you actually seeking to measure?