Tachometer

Discussion in 'Photos & Bicycle Builds' started by Arty, Sep 23, 2016.

  1. Arty

    Arty Active Member

    A while back, I decided to add a tach to my bike, so I ordered a "Whizzer" tach online, and modified it to work on my bike. The wiring is fairly basic -3 wires for the movement - hot, ground, and signal, and two for the tach light - hot and ground. You need a 12v battery supply for it to work - I'm using a rechargeable lithium ion.
    For the signal (trigger) I used the hot wire to the CDI.
    To mount it, I had to fabricate a custom mount, and cut apart a stainless steel soap pump for the case.
     

    Attached Files:


  2. zippinaround

    zippinaround Active Member

    or you can buy super cheap ones with that powers itself and just hooks up to the sparkplug only cost 5€ and no modifying or messing about , mine is still on its way but should be here soon hopefully
     
  3. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    I presume that you are using the tach on a 66 cc 2 stroke?
    Is it accurate?
    How much did it cost?
     
  4. Arty

    Arty Active Member

    Yeah - it's on a 66cc, and seems accurate - but I have no point of reference to check it.
     
  5. zippinaround

    zippinaround Active Member

    how exactly does one go about checking how accurate it is? fit it to something that already has a revometer?
     
  6. FurryOnTheInside

    FurryOnTheInside Active Member

    If you have measured your roll out (the distance of one wheel rev while you're actually on the bike) you should be able use arithmetic to work out how many RPM it does at a given speed. With a speedo set up with the accurate roll out as the wheel circumference, make a little chart and tape to the stem/bar to check it on a ride. :)
     
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  7. zippinaround

    zippinaround Active Member

    whats the formula to change wheel rpm to engine rpm?
     
  8. FurryOnTheInside

    FurryOnTheInside Active Member

    I'll use some nice round figures* for example but you must measure actual roll out.

    60km/hr = 1000m/min
    Divide by
    2m rollout*
    =500 wheel RPMs
    =500 rear sprocket RPMs
    Multiply by
    sprocket reduction 4 (10t:40t*)
    = 2000 drive sprocket RPMs
    Multiply by
    internal reduction 4.1 on the 2stroke
    =8200 RPM @ 60km/hr

    (8200÷ 6 ) x 5 = 6833.3 @ 50km/hr
    (8200÷ 6) x 4 = 4555.5 @ 40 km/hr
    Etc.

    :)
     
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  9. KCvale

    KCvale Motorized Bicycle Vendor

    I just use these.
    https://www.amazon.com/TMS-Digital-...474735032&sr=1-3&keywords=tach+and+hour+meter

    $10 and works with 2 and 4-stroke engines (read the manual to set it).
    It has an internal battery so just one wire coming out you just wrap arond the plug wire a couple times.
    When the engine is off it displays the Total hours the engine has been on.
    When the engine is on it displays RPMs.

    Simple, cheap, and good for about a year.
     
  10. zippinaround

    zippinaround Active Member

    Well my tachometer arrived today took all of two minutes to set up ! Seems my engine revs all the way to 4000 rpm hahah man that's bad !
     
  11. FurryOnTheInside

    FurryOnTheInside Active Member

    That is interesting. You didn't intend to build a low RPM engine?
    What is your top speed in km/h and what was your calculated engine RPM?
     
  12. zippinaround

    zippinaround Active Member

    No I didn't intend for it to be so low , I haven't taken it for a spin yet because I need to change my back wheel , but top speed was ~28 mph which is ~45km/h , it has been sitting for a while too will change fuel and wheel later and take it for a spin.
     
  13. FurryOnTheInside

    FurryOnTheInside Active Member

    Oh, so it definitely seems accurate, and that was no-load RPMs? Eek. I am hoping to build a low rpm engine and don't mind limited no-load RPMs but I hope it will rev a bit higher than that!
    I think you have your work cut out. Or to be more positive, you have found your fun winter project. ;)
     
  14. KCvale

    KCvale Motorized Bicycle Vendor

    You have it set to wrong mode, you are the mode where it only counts ever other spark.
    Change the mode and you'll have your 8K normal rpm display, hence why I stressed reading the manual to set it up ;-}
     
  15. GreatScottt

    GreatScottt Guest

  16. zippinaround

    zippinaround Active Member

    I set it to rpm 1 I'm pretty sure , will check again but that would explain the lowness haha
     
  17. KCvale

    KCvale Motorized Bicycle Vendor

    There is no wiring other than the single wire you just wrap around the plug wire.
    It is internal battery operated.

    Sure you can use that, but you'll have to carry a 12V battery to power it as it doesn't have an internal battery.

    I like a big old school analog speedometer/odometer over a tiny digital myself, especially in bright sunlight, a quick glance down tells me everything I want to know.

    [​IMG]

    Handlebars are a big thing with me, always has been since I built my first bike and decided the kit grips SUCKED!

    I usually just replace the grips with black BMX form grips as you can stretch them over the throttle barrel.
    Some bikes I motorize however have great grips like the hand stitched real leather foam grips in the pic above.

    But to get back on topic, anything you find for a Motorcycle expects you to have an on-board 12V DC power supply.
     
  18. zippinaround

    zippinaround Active Member

    KC what setting do you set the digital tach to? I had mine set to 2 stroke 1 cylinder and it would only read half revs I think it might have been programmed wrong because I set it to 1 stroke 1 cylinder now it reads properly , I think my pipe might be stopping it at 7k (not complaining) , but would be interested to know what you set yours to
     
  19. KCvale

    KCvale Motorized Bicycle Vendor

    Setting 2, a single cylinder firing on every revolution.
    A 4-stroke doesn't need to fire every RPM, it does exhaust and intake on one 1 rpm, but the engines fire the plug anyway so 1 spark every revolution.
     
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