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Thread: Shock dyno (or Shock absorber dynamometer)

  1. #1
    [email protected] tonyfoale's Avatar
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    Shock dyno (or Shock absorber dynamometer)

    A shock dyno is a measuring tool for analysing the dynamic characteristics of the the damper part of a vehicle shock absorber. Over the period of their existence there have been several basic types used. The main types in chronological order being;
    1. Mechanical
    2. Hydraulic
    3. Electric

    Hydraulic and electric are typically hi-tech and very expensive, controlled by computer they can driven to provide different wave shape displacements and can even be fed with real road data to simulate real life loading on the shock.

    Mechanical versions are the traditional and most numerous. A crank mechanism is used to convert rotary motion from an electric motor to linear motion to drive the shock. Modern machines use a VFD (variable frequency drive) to alter stroke velocity, and the crank radius is usually adjustable (either in steps or continuously) to alter the maximum displacement.

    My need is to develop rear shocks and front forks for classic racing motorcycles and my budget does not run to an hydraulic or electric device so I decided to build my own take on the mechanical type. The following shows the completed tool with an Ohlins shock mounted.

    Shock dyno (or Shock absorber dynamometer)-img_0041s.jpg Click thumbnails for full size.

    Some machines use the crank to drive a Scotch Yoke to give sinusoidal stroke motion, others use a long conrod relative to stroke length to get a close approximation to a sinusoidal motion, the latter is the type that I decided to build because I see no special benefit in a true sinusoidal motion as long as the displacement is measured against time throughout the stroke. The other parameter that needs to be measured is the force exerted by the shock in response to the applied motion.

    The following details the construction phase.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_01.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_02.jpg
    On the left is a 5 hp 3 ph motor which I kept from an old lathe which I had earmarked to power the machine. It was a flange mounting motor, I'd have preferred a base mounted type for ease of fitting. The start of the motor mounting is shown on the right being setup for making the holes for the mounting bosses.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_03.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_04.jpg
    Preparing holes for the mounting bosses and then machining the bosses level.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_09.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_10.jpg
    Attaching the motor mounting sub-frame to the base frame.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_05.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_06.jpg
    Here we have the motor mounting frame welded to the base, and also the mounting plate for a reduction gearbox.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_07.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_08.jpg
    Showing both motor and 25:1 reduction gearbox mounted to the part completed frame.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_13.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_14.jpg
    A couple of views showing the crank plate fitted to the gearbox output shaft. The tapped holes allow different maximum strokes of the shock.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_15.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_16.jpg
    On the left is the slider block and conrod. I had some 1" ID linear ball races so I got a length of 1" Thompson shaft and made an aluminium housings for the bearings. The shaft moves very smoothly with a high degree of rigidity. The yoke at the top is for mounting a shock or fork slider. The second photo shows a trial mockup of the assembly.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_17.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_18.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_19.jpg
    Making the top support bracket for the two uprights. Below are the two fixed lower mountings.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_20.jpg Shock dyno (or Shock absorber dynamometer)-shockdyno_21.jpg
    The sub assembly for mounting the bearing block and mountings for the uprights.

    **** Photo limit reached. To be continued.
    Last edited by tonyfoale; 03-17-2018 at 03:44 PM. Reason: Spelling

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    ****** Continued

    Shock dyno (or Shock absorber dynamometer)-shockdyno_22.jpg
    Testing alignment prior to welding of sub-assembly.

    Shock dyno (or Shock absorber dynamometer)-shockdyno_23.jpg
    Nearly finished, it just needs the load cell for measuring force, the string pot for measuring displacement and the top shock mounting yoke.

    Examples of shocks on test

    Shock dyno (or Shock absorber dynamometer)-marzocchiondyno.jpg Shock dyno (or Shock absorber dynamometer)-ohlinsfork.jpg
    On the left is an old Marzocchi fork for classic racing and on the right is a modern Ohlins race fork. Note the load cell and upper mounting yoke.

    Shock dyno (or Shock absorber dynamometer)-img_0042s.jpg Shock dyno (or Shock absorber dynamometer)-img_0045s.jpg Shock dyno (or Shock absorber dynamometer)-img_0046s.jpg
    Upper mounting fixtures for front forks.

    Shock dyno (or Shock absorber dynamometer)-img_0041s.jpg Shock dyno (or Shock absorber dynamometer)-sachs.jpg
    An Ohlins and a Sach rear shocks.

    The input voltage and output signal of the load cell are connected to a dedicated instrument amplifier, which together with the displacement info. from the string pot is feed into a LabJack DAQ (Data Acquisition) system which then passes it on to a laptop for analysis and plotting in some software that I wrote for it. I have also potted some temperature sensors in small aluminium housings which I attach to the shock. Thus enabling temperature sensitivity to be measured.

    Shock dyno (or Shock absorber dynamometer)-software-1.jpg
    Software opening screen.

    Shock dyno (or Shock absorber dynamometer)-tempsensor-1.jpg Shock dyno (or Shock absorber dynamometer)-tempsensor-2.jpg
    The temperature sensors. Note the concave block to better fit the shock body. For those shocks with an external gas chamber there is a 2nd sensor for that.

    Examples of test results

    Shock dyno (or Shock absorber dynamometer)-marzocchifork_sae15.jpg
    Older forks didn't always perform too well. Here are the diabolical characteristics of a standard fork. The problem was that the orifice for rebound oil was drilled such that it became blocked off way too early in the rebound stroke.

    Shock dyno (or Shock absorber dynamometer)-ohlins_f_d.jpg Shock dyno (or Shock absorber dynamometer)-ohlins_f_v.jpg
    The much better characteristics of modern cartridge forks. On the left is the force/displacement curves with the force/velocity curves to the right. The 3 different sets are with the damping adjustments set to different values. These curves are several repeated runs superimposed.

    Shock dyno (or Shock absorber dynamometer)-cavitation.jpg
    An example of cavitation due to insufficient gas pressure in the shock.

    One could write a book on shock dyno testing but the above is all that I have time for. Maybe it will wet a few appetites?
    Last edited by tonyfoale; 01-12-2017 at 05:28 PM. Reason: Additions

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    olderdan (01-13-2017), Paul Jones (01-18-2017), PJs (01-19-2017)

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    Thanks tonyfoale! We've added your Shock Absorber Dynamometer to our Motorcycle category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Thanks tonyfoale! We've added your Temperature Sensor to our Measuring and Marking category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    hello tony, beautiful and interesting dyno. did you made the load cell? riders being riders one would be better off connecting a shock dyno to a crystal ball then to the "subject" brain (or whatever we have for one - rider part talking hehe). thanks for sharing. any pics of pistons, valving stacks, chambers you want to share?
    pete

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    Quote Originally Posted by penca View Post
    hello tony, beautiful and interesting dyno. did you made the load cell? riders being riders one would be better off connecting a shock dyno to a crystal ball then to the "subject" brain (or whatever we have for one - rider part talking hehe). thanks for sharing. any pics of pistons, valving stacks, chambers you want to share?
    pete
    Pete,

    No I didn't make the load cell, that is an off the shelf item. The load cell itself is not overly expensive, but you need to have a decent instrument amp. as well. If I recall correctly the amp. was more expensive than one cell but I can use it for some other tasks which use other load cells. You can buy instrument amp. chips quite cheaply but you need filters etc. etc. I could have easily made an amp. but unless I got very lucky it would have required some development time which I would prefer to spend on developing the suspension.
    I don't have many pix. of the valving of the stuff that I have been working on because it was always a work in progress. I'll see what I have though.

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    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by DIYer View Post
    Thanks tonyfoale! We've added your Temperature Sensor to our Measuring and Marking category,
    as well as to your builder page: tonyfoale's Homemade Tools.
    I have made a new post going into more detail about the temperature sensors.
    Ruggedised temperature sensors
    For anyone who wants to go deeper into the subject.

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    Jon
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    Congratulations tonyfoale - your Shock Dynamometer is the Homemade Tool of the Week!

    We had an extraordinary week around here, guys. We broke our years-long record for the most pageviews on our forum, and we did it in style - with a huge list of great homemade tools, many of which could've won this award in another week.

    I'm still processing all of the new members, and all of the new different forums linking to us - literally hundreds of different forums, representing every different DIY discipline under the net. The value of the high-end technical contributions that we're making to internet culture is unprecedented. That we're able to do this with such a high signal-to-noise ratio of technical content with virtually nonexistent drama, is a rarity among forums, and a testament to the quality of the contributors that post here.

    A roundup of some of the nicest tools from this week: a Metal Bender by Vyacheslav.Nevolya, a Power Hacksaw by olderdan, a Lathe Belt Grinder by connan, Work Stops by mklotz, a Bridgeport Mill Upgrade by tonyfoale, a Magnetic Building Board by jjr2001, and a Countersink Gage by rgsparber. It was also a good week for homemade automotive tools, with: a Tire Spreader by dtech, an Engine Locating Jig by astroracer, a Front Shock Mockup Tool by astroracer, and two different carburetor work stands, including a Carburetor Work Stand by astroracer made from a carb spacer, and another Carburetor Work Stand by bobs409, made from old valves.

    And yet another great milestone - this is tonyfoale's third Homemade Tool of the Week win, which means we have another 3-Time Tool of the Week Winner! You'll notice the 3-Time award trophy graphic in tonyfoale's postbit beneath his avatar.




    Here are all of your winning tools:




    tonyfoale is in good company among this list of previous winners: rossbotics, mr95gst, Paul Jones, Christophe Mineau, immortalx, scorch, Brendon, Frank S, mklotz, Vyacheslav.Nevolya, jjr2001, and olderdan (all awards are viewable here).


    tonyfoale - the cash prize is a $25 online gift card, in your choice of Amazon, PayPal, Giftrocket, or bitcoin. Please PM me your current email address and gift card choice and I'll get it sent over right away.


    Congrats again and nice job!

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    thanks for the reply tony, yes the amp really is an issue with load cells, i tried to cheat with a very crude version and homemade strain gauge but had endless problems of delamination of the gauge, noise and general unreliability so i gave up. sadly here these instruments are prohibitive but then again one does with what one can have. edit: this was many many years ago when i was a young lad employed in a mx tuning shop. so that was memory served
    hope you find some pics it`s always interesting to see what other tuners do to mod susp internals.
    a suspension dyno would be a dream too even if stuck to one or two tyre compounds
    thanks again. pete
    Last edited by penca; 01-21-2017 at 02:23 PM.

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