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  • suspension travel sensor?

    Anyone know of any (perferably cheap) ways of reading suspension travel? something like a variable resistor that changes resistance the more you compress the shock? Looking at making a data-loggerfor my truck

  • #2
    You could use a magnetic sensor mounted to the frame coupled with a permanent magnet on the suspension. I'm not sure if the response time would be quick enough, but it;s worth a shot.

    -g.

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    • #3
      Originally posted by flipster125
      Anyone know of any (perferably cheap) ways of reading suspension travel? something like a variable resistor that changes resistance the more you compress the shock? Looking at making a data-loggerfor my truck

      Please tell us more. Like, each individual wheel, how accurate must it be, does it have to be completely linear, how much resolution (6 inches, 1 inche, centimeter, millimeter, decameter etc.....)

      That will help.

      Michael
      ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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      • #4
        12 inches long, minimum accuracy ~1 inch (ie be able to tell if it's 1 inch, 2 inches, 3 inches etc, more accurate is better, but not neccessary)

        It's also linear, somethings wrong if your shock isn't moving in a linear motion :P

        I only need one wheel, (if I need to, I could just make more and put them on other wheels)

        Thanks

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        • #5
          Originally posted by flipster125
          It's also linear, somethings wrong if your shock isn't moving in a linear motion :P
          I didn't mean whether the motion was linear, whether you needed it to be linear, such as 1,2,3 or 1, 2.5, 5, 9, 12.

          First, why do you need to be able to tell how much the suspension is moving?

          Next,

          Here are the issues I see. Attaching something to the suspension that won't move no matter what.

          While you think that the suspension moves up and down, it DOES NOT move in a straight line up and down. The is some lateral movement. There has to to be because the ??lateral links?? remain a constant length in the suspension. Also, your strust is NOT mounted directly above your where to go straight up and down.

          So, a variable resister won't work because there is none that has 12 inches of travel that I know of. Also, they are not the most rugged piece of equipment that you would want to mount it outside the car, especially in the wheel well. Then you have to connect the varister with the suspension some how, to measure the motion.

          Magnets might work, but you run into a problem with the resolution. Magnets have a "field" which would cause multiple magnets to be sensed at the same time.

          Sorry, can't think of anything right now

          Michael
          ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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          • #6
            Use a spring and a PIC, as the spring stretches, its resistance will increase, so you can measure that with the ADC on the PIC voila!

            Got this idea off of Myth Busters, although they didnt use a PIC, they used it to determine the whiplash Buster would endure during the Airplane seating/crash myth, and measured it with a DMM Ohmmeter.
            Hey Laserlips, your momma was a snowblower!!

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            • #7
              Originally posted by adaminc
              Use a spring and a PIC, as the spring stretches, its resistance will increase, so you can measure that with the ADC on the PIC voila!

              Got this idea off of Myth Busters, although they didnt use a PIC, they used it to determine the whiplash Buster would endure during the Airplane seating/crash myth, and measured it with a DMM Ohmmeter.
              That is sooooo cool. But how do you calibrate something like that??

              Michael
              ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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              • #8
                I think a "String pot" (one of many names) may work well for this. Basically, it is a thin cable wrapped around a spool mounted to the end of a multi-turn rotary pot. So you just have a flexible cable providing the length, rather than the actual resistive element. There is some sort of coil spring that pulls the cable back in I guess... Here is a link to a picture that probably describes the concept better: http://www.celesco.com/faq/cet.html

                I don't know much about sources of inexpensive units, you might be able to build something yourself with a 10-turn pot, a spool, cable, and something to retract the cable. For more info, google string pot or cable-extension transducer. Not sure how quick they will react (recoil), probably depends on inertia, recoil spring tension, and pot friction.

                Sounds like a neat project, would be cool to do on my bike to help tune the suspension. Here is a link to a commercial unit called the ShockClock that uses long linear pots for suspension travel pickup. http://www.race-tech.com/SubMenu.asp...es&showPage=da

                Have fun!

                Andy

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                • #9
                  I like the string pot for this.

                  I'm not following the spring thing. Expecting it to act like strain gauge?

                  A rotary pot placed at suspension-chassis pivot point and an arm on the wiper attached to the moving parts should track reasonably well.

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                  • #10
                    Hey this sounds neat, but what is the overall goal here?
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                    • #11
                      Why not use the linear potentiometers that were designed for this application?
                      If you want a DIY approach, use http://www.globalspec.com/FeaturedPr...romSpotlight=1.

                      If you want a much simpler, more expensive pre-made datalogging package, get the Edelbrock Qwikdata.
                      http://www.edelbrock.com/automotive/...wikdata_1.html

                      Just search Google for Linear Potentiometers. There's lots available. The first link I posted does almost a full 12" of travel.

                      I plan on doing Datalogging one of these days, just gonna be a while. It's low on the list.


                      Cheers,

                      Kris
                      How Much Horsepower Can I have And Still Go To Heaven?

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                      • #12
                        The spring idea works on basic electric theory (ohms law), as the length of the spring increases (stretching it), the resistance increases, it will work sort of like a pot, or a ribbon controller, calibrating it would take some R&D, i'm not sure if its linear or logarithmic, benefit of using a spring is, it doesnt matter if it gets all dirty n' stuff easy to wash off, and very cheap!

                        Come to think of it, you might be able to use the springs already on your vehicle!

                        If you want to test it out, its easy, just attach 1 terminal of an ohmmeter to 1 end of the spring, and the other terminal to the other end, then stretch the spring, you will see the resistance increase
                        Hey Laserlips, your momma was a snowblower!!

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                        • #13
                          Originally posted by adaminc
                          The spring idea works on basic electric theory (ohms law), as the length of the spring increases (stretching it), the resistance increases, it will work sort of like a pot, or a ribbon controller, calibrating it would take some R&D, i'm not sure if its linear or logarithmic, benefit of using a spring is, it doesnt matter if it gets all dirty n' stuff easy to wash off, and very cheap!

                          Come to think of it, you might be able to use the springs already on your vehicle!

                          If you want to test it out, its easy, just attach 1 terminal of an ohmmeter to 1 end of the spring, and the other terminal to the other end, then stretch the spring, you will see the resistance increase
                          After it was mentioned, I thought about using the stock spring. Might be possible.

                          Also, wanted to say that your quote of "Johnny #5" is classic, and made me smile.

                          Michael
                          ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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                          • #14
                            strain guage is a good idea, but it need s to be calibrated and works well under short distances. also, your shocks go over time, so it needs to be recalibrated every so often. Starin gauges are cool and cheap. I had a proejct to make a scale out 4-8 of them of one this year.

                            A decent idea is not to measure from the spring, which deforms over time, but to measure from the wheel. Why not use a promximity sensor (a photocell and ir lamp/led) in the wheel well. Theyr'e cheap ($10 for a pair at most) easy to use, and you can have it recalibrate with ease. Plus, when you change your springs, which are changed more than a wheel well, or a fat guy sits in your passenger seat, its no bigge.cause when you're stopped, press a button, instant back to 0, and its all good. The only thing that might throw it is if you drive in mud and cover the sensor, the tire's color changes, or its an exceedingly bright light. But once again...press the button and rest. Ofcourse, that will through off the distance calibration, but since its digital, teh values are all logged, so you can apply a function later maybe. but like i siad, its a decent idea, not a perfect one.
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                            • #15
                              This is a job best done using an LVDT!

                              Clink for ONE Example

                              "Linear Variable Differential Transformers are linear position sensors that are used in harsh industrial or aerospace environments where reliability and/or performance requirements exceed the capabilities of potentiometers. LVDTs have no sliding electrical contacts to corrode or wear. The only moving part is a more or less inert chunk of iron."

                              The best part about an LVDT is the fact that you can make them easily yourself and they can be made to accomodate any length of travel. (You can wind wire, can't you?) The worst part is the fact that you'll need a circuit to drive them and produce a DC output that's proportional to position. (Although, some clever software and a Sound Card could be very effective!)

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