Measuring a force or pressure between two surfaces

godtabh

Two surfaces are in contact and rotate around a pivot. How would you measure the forces between?

What I am trying to measure is something like below

https://www.youtube.com/watch?v=k5DIwAveY7w

I'm looking for a practical approach as opposed to a theory approach. Would some sort of pressure sensors work?

enda1

Can you install a load cell in the pedal?
Mill off the top of the pedal to the depth of a small profile load cell then use that as the bearing down pedal surface?

I presume this is for a stationary bike in a lab rather than an on road data acquisition application?

These guys have something like it it seems

godtabh

that looks exactly what I am looking for.

Power meters has me intrigued. I know a small bit about the end user side of things but nothing about the engineering and I just want to investigate the engineering process to understand the cost

Turbulent Bill

I don't know much about them, but AFAIK most commercial power meters use torque sensors on the bottom bracket's axle. You could probably use strain sensors on the cranks as an alternative too.

There was an Irish company developing a pedal - based system a while back, don't know if it got off the ground. The good folk in the Cycling forum probably have the details.

2011

How about this?

godtabh

2011 wrote: »

How about this?

Thats the end product. I want to understand how to get there

godtabh

Turbulent Bill wrote: »

I don't know much about them, but AFAIK most commercial power meters use torque sensors on the bottom bracket's axle. You could probably use strain sensors on the cranks as an alternative too.

There was an Irish company developing a pedal - based system a while back, don't know if it got off the ground. The good folk in the Cycling forum probably have the details.

There are 3 main types of pm.

One in the rear axil, on in the pedals/cranks which both measure direct force and the other measures wind resistance to determine the force required to push you through it.

The Brim Brothers are developing the Zone PM

Turbulent Bill

godtabh wrote: »

There are 3 main types of pm.

One in the rear axil, on in the pedals/cranks which both measure direct force and the other measures wind resistance to determine the force required to push you through it.

The Brim Brothers are developing the Zone PM

Using wind resistance sounds a bit hokey - I wonder what happens to the power readings if you're grinding up a steep hill?

godtabh

Turbulent Bill wrote: »

Using wind resistance sounds a bit hokey - I wonder what happens to the power readings if you're grinding up a steep hill?

my understanding is that it measures the wind in one direction. Your speed in the other direction and balances them out to come up with a force.

It is a bit hokey as apparently they arent very good in the rain!

Carawaystick

Turbulent Bill wrote: »

Using wind resistance sounds a bit hokey - I wonder what happens to the power readings if you're grinding up a steep hill?

wouldn't they just use height/time measurements?

Turbulent Bill

Carawaystick wrote: »

wouldn't they just use height/time measurements?

Maybe, as in energy expended to lift bike and rider over a certain height? I think you'd need a mass measurement for this, as well as some way of measuring small changes in height.

It could work great, but on the face of it is a really perverse way of measuring something pretty simple.

darragh o meara

A couple of lads in college this year done a project on this very thing, They used a load cell on the crank and fed the data back through a slip ring to a Labview Daq. Ill see if I can get a copy of their thesis for you.

It was an interesting project and they were able to get some decent results form it, although Iknow they had hassle with making it mobile and ended up running the bike on a turbo trainer. Perhaps a battery powered arduino and sd card reader would sort the issue.