Measuring roller skate wheel rotation

[londevitt]

Hello, I want to build a machine that will detect (and thus measure) the rotation of a roller skate wheel as it sits on a roller skate.  The purpose here is to get a quantitative measurement of the bearing units quality.  The plan is to build a machine that will apply a standardized force vector to the wheel and then time how long it spins a result.

Can anyone suggest what is the best kind of sensor to use to detect the rotation of the wheel?

If this is not the correct forum for this question I apologize.

Thank you,
\Lon.

[Herman the German]

Hi Lon,

I assume the roller skates are fixed to a test stand.

Using a permanent magnet on one side of one wheel and a counter weight on the opposite side you won't have any unbalanced situation affecting bearing life time.

Use a hall switch to sense magnet passage (magnet must face the sensor with it's south pole) you can count revolutions employing a simple counter circuit.

Check out the TLE4905 for your purpose and decide if it fits your needs.

HtG

[rfranzk]

Hello all,
  What about using a non contact tachometer that uses a refelective tape applied to the rotating surface? This would eliminate or reduce any balance problems using magnets and weights. Take a look at the link for one.

rfranzk.          http://www.amazon.com/Neiko-Professional-Digital-Non-Contact-Tachometer/dp/B000I5LDVC

[londevitt]

Thank you Herman the German and rfranzk your input is much appreciated. 

You are correct in thinking the skate will be on a stand.  The application would be a machine in a skate shop or rink where skaters can place their skates and find out how good their bearings are as measured by how long each wheel spins from the standardized force.

I will draw a diagram of the machine and post it for your further comment.

The (magnet/sensor) Hall Effect idea is something I have thought about but abandoned as to cumbersome for an end user device; I am strongly gravitating to doing it optically.

Especially as I am an engineer for an electronics security company and have access to video cameras/DVRs that can do motion detection and alarm circuit triggering which I could then use to control timing circuitry.

Thank you again for your time and consideration.
\Lon.