# Powermeter project.

#### AEROisKING

As part of a school project I am making a powermeter that is embedded in the sole of a pair of shoes. I'm having issues with deciding what sensors and processors are required.

At present my design consists of 4 flexiforce sensors in each shoe. Would any one be able to tell me if these sensors are suitable and if so what processor would be suitable?

Thanks
Will

#### fatsprintking

I dont know how you are going to go here. You really need to be looking at a strain gauge, where the flexiforce sems to be more designed to be a switch trigger. It seems like it will measure a change in force, but I am not sure it is going to be able to give an accurate value to it.

I also would have thought you would almost need to be designing your own processor for this type of application, as I am not sure you are going to find someting generic which is going to work on what is a pretty unique idea.

Not to rain on the parade, but the other issue you have with a shoe based system is that it is only going to measure downward force. It may be able to give a maximum force value, but it is going to change if the rider is standing or sitting and the level of incline they are on regardless of the actual increase in power, simply because there will be more weight on the shoe.

Good thinking outside the box however and I would be interested to see how you go.

#### meandmygitane

1. Since the shoes are not rigid I should think the force sensors will need some "fudge factor" (the force could be unevenly distributed over the soles).

2. Will the force be perpendicular to the force sensors plane and measure it rightly? No idea. And a non-zero force can mean zero work.

3. Should think a PIC microcontroller could do the job

4. Power is force integrated over along a curve, so you have to measure a second quantity, that is the displacement (easier on a bike because it is measured by the numbers of rotations of the crankset times the) which maybe forces the use of another sensor like an accelerometer.
The integral is probably best solved by chopping it up in very small bits between each sample, or between two averages of multiple samples.

5. Good luck, I think you will need an accelerometer per shoe (or maybe just one working for both?), force sensors and a PIC.

#### DirtyWorks

meandmygitane said:
1. Since the shoes are not rigid I should think the force sensors will need some "fudge factor" (the force could be unevenly distributed over the soles).

2. Will the force be perpendicular to the force sensors plane and measure it rightly? No idea. And a non-zero force can mean zero work.

3. Should think a PIC microcontroller could do the job

4. Power is force integrated over along a curve, so you have to measure a second quantity, that is the displacement (easier on a bike because it is measured by the numbers of rotations of the crankset times the) which maybe forces the use of another sensor like an accelerometer.
The integral is probably best solved by chopping it up in very small bits between each sample, or between two averages of multiple samples.

5. Good luck, I think you will need an accelerometer per shoe (or maybe just one working for both?), force sensors and a PIC.

The major hurdle I see with this idea is the space constraints. A shoe-based system will have boxes and a power supply to attach somewhere on your person. Kind of whacky.

I like strain gauges strategically fastened to the frame. It seems to me that this would be difficult enough to get working for a school project.