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Thread: suspension travel sensor?

  1. #11
    Variable Bitrate Superduck's Avatar
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    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.


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    Kris
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  2. #12
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    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!!

  3. #13
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    Quote 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
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  4. #14
    FLAC
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    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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  5. #15
    Constant Bitrate NiteMax Mark's Avatar
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    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!)

  6. #16
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    The string idea sounds wimpy... I would be woried of it getting snagged. I would think that attaching something to the a arm pivit point would be most secure way of doing it... best way would be a sensor on the shock itself like you spoke of that would sense travel or read tick marks sorta like the hallofect (sp sorry) pickup or abs sensor. Only issue with this is its variable, not absolute, it would loose track if it wasn't sensing while the shock changed, like if you loaded your truck while the computer was off.

    Strain gauge might work for this.

  7. #17
    Variable Bitrate portabuddy's Avatar
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    Toilet Training

    Pardon my ignorance but i think that you guys are over-complicating things., why make everything when you can use pre-made sensors

    I had a idea reading this log, why not use a toilet approach...,
    I know what your thinking, he's crazy, but it been used in cars and trucks for years. Think fuel tanks, if you can get your hands on a float-type or Linear potentiometer fuel level sender then you can mount it depending on type of vehicle, since you mentioned that it has 12in. of travel than its either a rock crawler, SUV or a transport truck of some type. then the question is is it a coil or a leaf spring, if its a SUV, pick up or a rock crawler then it would most likely be a coil spring and therefor independent suspension. in this case you have two options there is a magnetic center post style where there is a magnet that travels along a center pole that induces a current, you could mount this style along side your shock(there are models that are 14" long,like in a fuel tank of a 03'-06' Volvo truck) or a Linear potentiometer style that travels in a arc, this type works like a rotary dill, where there is either a pin that travels along multiple posts or a enclosed potentiometer like a TPS(throttle position sensor) this type works on resistance and requires a input voltage, some models even use a internal rotary pot. you can use this with a leaver arm connected to the lower controle arm to measure your suspension travel. you can easily use a gage(modify a fuel gage to read distance(in mm/in.)) or use a make a simple circut and connect through one of your com port for input. very simple and you can probably salvage all the parts for nearly free

    here is a pic of what i mean, on the left is the central post magnetic ring style and on the right is the linear potentiometer. both types used in the top tanks of toilets.lol. only instead of a water valve they have sensors.

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  8. #18
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    I think a non-contact sensor that does not require being in physical contact with anything would be the best. There are various types of optical sensors that are used for this, but i think your best bet is an ultrasonic sensor. These are compact, durable, and give an easy to read linear current or voltage output. Additionally they can be powered off 12vdc. Expect to pay about $300 each.
    They look like. As you can see they are very small and rugged. Just mount it to the frame and point it at a suspension part that moves

    You will have sub-millimeter resolution and repeatability with about a 50ms response time. The linearity is about +- 1% on most models, so you will need some scaling if you want to take advage of the full precision.

    High end linear potentiometers like these: http://www.celesco.com/linearpot/index.html are also good, but need to be mounted at both ends and are likely to be even more pricey.

    Other options include linear optical encoders, linear capacitive sensors, linear autotransformers, laser triangulation sensors, strain guages, flexion sensors, etc, but these all have various disadvantages.

    I think the spring trick mentioned earlier presents some promising possibilites of you are looking for a low budget route.

  9. #19
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    I didnt even think of ultrasonic, that would probably be the best thing to use, hell, you could probably build one, with a ultrasonic transmitter, reciever and a small PIC. maybe use some passive bandpass filtering.
    Hey Laserlips, your momma was a snowblower!!

  10. #20
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    You don't want anything optical (has anyone heard of dirt?). You're going to need something that mounts to your axle and frame (depending on vehicle). You also need something thats weather proof, and is going to last more than 30 minutes.

    Linear Pot, or the "Shock Clock" looks like the best 2 links on this page. You're going to spend a couple hundred bucks on this.

    The spring idea might work for a little while.. but don't you have to isolate it from the chassis ground? And what happens when you drive through a puddle and it gets splashed with water/dirt? Plus, I imagine as the spring wears, your resistance will change. Plus its going to be easily subject to damage (assuming its a thin spring.. first stick/road trash and its gone).

    Another idea... several vehicles out there (passenger vehicles) have "active suspension" which consists of a rugged linear pot, and an adjustable shock system. Look up a make/model, and visit your local auto parts place. Maybe you can pickup a sensor already designed for automotive use for a good price. The only thing thats going to be tricky is mounting it since your truck might have 12 inches of travel as you say, and the sensor only gives you 4. Mounting closer to the frame on an independant suspenion, or on a track bar or something would work.

    -Chris

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