Measuring roller skate wheel rotation

Discussion in 'The Projects Forum' started by londevitt, Jun 1, 2011.

  1. londevitt

    Thread Starter New Member

    Jun 1, 2011
    2
    0
    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.
     
  2. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    I suspect you haven't thought about the physics of what you're trying to do in detail -- but that may come once you get some experimental data. :D

    You don't say what exactly you want to measure. Do you just want to see how long the wheel rotates before stopping? Probably the least intrusive measurement would be to put one or more marks on the wheel and detect these marks moving past a sensor optically.

    But before you invest any energy in designing some hardware, start off incrementally. You can use a video camera to record the rotation of the wheel and get yourself some data fairly readily with little work (other than the labor to watch the video and derive numbers e.g. from frame timing). Put a digital stopwatch in the picture to help with timing. This will let you determine the standard deviation of your measurements -- which then will give you an idea about the discriminatory power of the experiment.

    Before you invest more effort, you might write up your experimental plans and post them for critique. You'll find that independent eyes can often see things you're blind to or haven't thought about. If you do this work, you're probably interested in making some decisions with the data (or, you could just be doing this out of curiosity -- that's OK too). Showing us your goals and intents along with the design can only help you make better use of your time and resources...
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    +1
    Your description suggests a simple stopwatch - to time how long the wheel spins after the "force vector" is applied - would do the job nicely. Measurement error caused by the human would be small compared to the total spin time. If you can't live with that, the video camera suggestion is a good one. Max error then is 1/30th or 1/60th of a second.

    Instead of applying a "force vector", which I assume simulates a hand spin of the wheel, consider applying a know rpm - maybe a drill press or a hand drill - to spin the wheel up to a known rpm and then time how long it spins. Is that what you're after? What you really need, I think, is a dynamometer to measure the torque required to spin the wheel at a given rpm.
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    Different, but maybe close, was a project I did for the local bike team. As part of thier training, they wanted an energy expenditure profile of thier course, as a means of helping to decide where to apply thier training. We hooked up a couple of strain gauges on the pedal webs and monitored web stress along with bike speed. By analizing the resulting profiles, they derived different exercise programs accordingly.

    You could drill and embed a small magnet into your wheel and pick up on the axle.
     
  5. londevitt

    Thread Starter New Member

    Jun 1, 2011
    2
    0
    Thank you someonesdad, wayneh and GetDeviceInfo your input is much appreciated.

    My purpose here is to get a quantitative measurement of a bearing unit’s quality as measured by the length of time the wheel spins when a standard force is applied to it. 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 certainly draw a diagram of the machine and post it for your further comment.

    Both the ideas of using a video camera and an electric motor to turn the wheels seem very good to me, 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. Using an electric motor seems better than the solenoid I was thinking about using.

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

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

    Senior Member

    Jul 7, 2009
    1,585
    141
    You might want to do some basic engineering homework before you invest any more time. One flaw I suspect in your reasoning is that you're assuming a bearing's no-load time-to-spin-down behavior is a good measure of quality of that bearing. I"d want to validate that assumption by going to the library and learning something about bearing theory and practice. How does that spin-down time relate to the quality of the bearing under load? Is it even relevant?

    In other words, find out what and how the bearing industry defines product quality and its measurement. I used to work in a place that used high precision ball bearings in their products (disk drives) and they invested lots of engineering effort into testing them. Believe me, that kind of investment is quite beyond what a single person would likely be able to do.

    And if you're thinking of making this a product (i.e., some skater will plop some money into a machine and have their skates measured), I'd sure do some market research to see if there's a demand for such a service. I'm not a skater, but I'd be a bit surprised if there'd be enough people to pay to have their skates analyzed to make the thing a money-making proposition. On the other hand, you might be able to create a new market. That's the fun and uncertainty of free enterprise. :p
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    I would think that differences in rotational inertia might also scupper this idea, unless all the wheels are of very similar design, or else you have some means of allowing for it.

    Another factor might be the characteristcs of any lubricant used. A tiny amount of viscous friction could have a profound effect on the spin-down time, without making any appreciable difference to the performance in service.
     
  8. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    I totally missed what it was that you were trying to do.

    There are a number of characteristics of bearings that will affect your spin down. The type of seals/shields will have a major affect. New bearings will spin down very quickly due to the seal/shield contact on inner and outer races. The most obvious signs of bearing degradation is a ruptured seal. It indicates a loss of lubricant and intrusion of pollutants. High load rated bearings (ball), typically have a filler slot in the races which allow extra balls to be inserted. This would be a higher quality bearing, and will spin down quicker than a normal bearing. Your lubricant will also influence your spin down.

    Spin down is not a good indicator of quality. Your best indicator will be to hold the wheel firmly and rotate it feeling for roughness.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I'd like to ditto this.
     
Loading...