Super Simple Tacho

Discussion in 'Motorized Bicycle General Discussion' started by Fabian, Sep 30, 2009.

  1. bandito

    bandito New Member

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    Isnt there a tac you can just hook up to the cdi or plug wire to work?
     
  2. Kevlarr

    Kevlarr New Member

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    Problem is the engine is already geared down so the sprocket is not the same as the engine's RPM. Crankshaft = little gear and clutch = big gear.
    [​IMG]
     
  3. Fabian

    Fabian New Member

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    Hi bandito

    Yes you can hook up a tacho which works of the sparkplug lead but it costs more than a $15 K-mart pushbike speedo and $3 worth of heatshrink tubing.
     
    #23 Fabian, Sep 30, 2009
    Last edited: Sep 30, 2009
  4. Fabian

    Fabian New Member

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    Hi Kevlarr

    I've already done the maths and worked back through the jackshaft ratio and the engines primary reduction gear ratio (big and small gear) to tell the bicycle speedo what circumference it needs to be using for an accurate readout in kilometers per hour, that reflects engine rpm.

    Just do my conversion, follow the instructions and you'll be amazed that the bicycle speedo reads the engine rpm correctly.
    I've taken my bike to three engine shops and they've confirmed with their electronic tacho's hooked up to the sparkplug lead that the bicycle speedo is in fact reading the correct rpm's

    Just do the maths yourself and you will understand how it works and why it works - "there is no problem".

    Fabian
     
    #24 Fabian, Sep 30, 2009
    Last edited: Sep 30, 2009
  5. noco

    noco New Member

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    there has got to be a simpler tack...is there some way of using those primary ignition circuits already on you handle bars(your kill switch)....other than that i got a timing light with a tack...its inductive off of the secondary ignition...a normal car tack works off the primary ignition...there has got to be some kind of product out there for single cyl. 2 strokes...
     
  6. Fabian

    Fabian New Member

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    Hi Noco

    Maybe there is a more simple tacho but if you can find one for under $20 that doubles as a spare pushbike speedo and also holds max rpm and average rpm, please let the rest of us know.

    Fabian
     
  7. xlite

    xlite New Member

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    There are tractor/lawnmower units that cost about the same as these speedos. I bought a half dozen a couple years ago and they work great. Unfortunately no links ATM.

    The "Tiny-Tach" brand are mostly for planes and outrageously overpriced.
     
  8. BarelyAWake

    BarelyAWake New Member

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    o_O

    $36 for a proven, quality, and multifunction tach isn't really "outrageous" - tho I can see merit and certainly respect the do-it-yerselfer, even saving a few bucks but you really need a touch of perspective lol Have you priced replacing the entire tach unit on a new Honda motorcycle, or even just a taillight lens? heh, these TinyTachs are a great product for those that just want to stick a good, reliable gauge on their bikes w/o fuss or hassle.

    Another way of lookin' at it is $15 bucks or so fer yer parts + say $10 per hr labor rate = about the same price as a TinyTach. The only difference being the justifiable pride in making something yourself.

    They're for far more products than just planes lol - perhaps you've been shopping in all the wrong places ;) The reason they're so popular amongst ultralight aircraft owners is their absolute reliability - an airplane is no machine for failures and a tach is a critical instrument for flight.

    Tiny-Tach: Gasoline Tachometers
     
    #28 BarelyAWake, Oct 1, 2009
    Last edited: Oct 1, 2009
  9. xlite

    xlite New Member

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    Certainly outrageous for bike when it costs half as much as a new engine. And you can get units with similar function for 1/3 the cost.

    Maybe SOMEBODY owns stock in Tiny-Tach factory? :)
     
  10. BarelyAWake

    BarelyAWake New Member

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    Nope - I jus like 'em ;) and there's folks like this;

    I gotta point out that these awesome bike engine kits @ $150 really skews a budgetary perspective - I've fallen victim to that myself lol

    Gawd - I remember buying both marine and real aircraft parts, if you want truly outrageous prices lol Even just actual motorcycle bits really can put a hurt on the 'ol wallet!


    edit: Despite all my going-on bout TinyTach, I still haven't gotten one fer my bike yet. If ya could manage to dig up a link or two for these "$10 tractor tachs" I'd be more than happy to check 'em out - not like I wouldn't mind savin' a few bucks myself lol, I've just NEVER seen a $10 gauge worth buyin'
     
    #30 BarelyAWake, Oct 1, 2009
    Last edited: Oct 1, 2009
  11. xlite

    xlite New Member

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    Unfortunately I'm at the vacation house now waiting for foliage to change. Won't get back home for a couple weeks (another 300 mile BIKE trip). I'll see if I can find an invoice or read labels then. There were 2 models, one about $15 shipped and another slightly smaller and cheaper. Meanwhile Google is your friend (maybe :) ).
     
  12. EnFlaMEd

    EnFlaMEd New Member

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    Engines kits in Aus range from $200-$350 depending on where you shop. I am actually keeping my eye on some 99c auctions on proper tachs at the moment though to see if I can score a bargain. If not I'll be building one of these myself.
     
  13. xlite

    xlite New Member

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  14. Fabian

    Fabian New Member

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    Certainly it's a good price and the sample time is reasonable - although not really relevant for a tacho (but i like the feature and it's important to me) it doesn't hold max rpm and average rpm.

    In Australia, i haven't found a small compact tacho for under $80, some priced as high as $250
    A $20 pushbike speedo calibrated to accurately read RPM with features that the others don't have, was an option too good not to experiment with or pass up.

    Fabian
     
  15. Norman

    Norman LORD VADER Moderator
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    I kind of glanced at this post on the home brewed tach. I'm wondering why you couldn't attach the speedo pick up right on the mag coil so the sensor could pick up the magnets on the rotor as they go by? There is enough space on the mags. coil at the back where I mounted a home made coil to power up an extra head light.
    I don't know if the speed sensor will work there with the rf that the engines put out but its just a passing thought maybe one of you guys might want to give it a shot?
     
  16. xlite

    xlite New Member

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    I suggested that in post #5. The sensor (reed sw) works but unfortunately range of calibration on my unit did not allow useable RPM readings.
     
  17. bairdco

    bairdco a guy who makes cool bikes

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    i love tacos.
     
  18. AnthonyX99

    AnthonyX99 New Member

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    would 5 inch range work if i where to put the sensor by the magneto
     
  19. noco

    noco New Member

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    i dont know about the voltages put out by the manito compared with the voltages induced into that tach's sensor but it sounds like they do the same thing so why wouldnt the coil primary wires work???other than voltages
     

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