Motorised Bicycle Tacho - Super Simple & low cost

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

  1. Fabian

    Fabian Well-Known Member

    G'day all

    I've had enough of being in the land of unknowns with lack of displayed RPM's.
    Necessity being the mother of all invention has found the solution.

    I've taken the liberty to make a super simple motorised bicycle tacho that can double as a spare speedo if the original speedo computer kicks the bucket.

    Step 1: Go to the SickBikeParts website and buy yourself the Deluxe Jackshaft Shifter (shift) kit and optional accessories to make your Chinese motorised bicycle engine more reliable.

    Step 2: Go to K-mart and buy yourself a 9 function Huffy bicycle speedo or two of them if not having a speedo in the first place.

    Step 3: Go to your local electronics store and buy 2 meters of the second finest wire available (i used 1 meter red and 1 meter blue wire for easy identification).
    Cut the bicycle computer speedo wire about 6 inches from the programable bicycle computer and very carefully cut the outer insulation, peeling back the two inner wires.
    Carefully cut the insulation from the inner wires, maybe leaving about 10mm of exposed copper wire.
    I found the original speedo did not have a long enough wire to secure the computer head to my handlebars from the Jackshaft output sprocket location.
    Maybe a different manufacturer of bicycle speedo's has a longer length of wire with their product- you can report back on that if finding something more suitable but it's a question of keeping it low cost.

    Step 4: Whilst at the electronics store grab yourself a length of heat shrink tubing to fit over the insulation of the individual 1 meter wire lengths; also get yourself a length of heat shrink tubing to fit over both the 1 meter wire lengths, to keep them nicely bound together.
    As i don't have a soldering iron, i just twisted the exposed copper ends of the pushbike speedo wire and the extra 1 meter lengths together, slipping the 3 inch lengths of heat shrink tubing over the top of the twisted copper wire sections (make sure you put the heat shrink tubing on the wire before twisting together).
    CAREFUL you get the polarity of the wires correct before heatshrinking everything.
    You can connect the wires both ways and the speedo will work but if you connect it back to front, the icon in the top left hand corner, indicating if you are moving forwards or backwards will be wrong when you are moving forwards.
    Try the setup with the wires connected one way or the other till you get it right.

    Step 5: Once everything has been heat shrinked together, mount the sensor pickup on the Jackshaft metal plate with plain old superglue (cyano), and also the magnet on the inside drum face (face closest to the sprocket teeth) of the Jackshaft output sprocket, making sure it clears the chain and the sensor pickup.
    You will have to carefully cut off the threaded stud on the magnet for it to clear the chain and Jackshaft output sprocket teeth.
    NOTE, NOTE, NOTE - make sure the surfaces you are gluing onto are absolutely spotless and totally free from grease or oil - MAKE SURE EVERYTHING IS SPOTLESSLY CLEAN or the superglue or any other type of glue will fail to hold - YOU HAVE BEEN WARNED.
    When finished, there should be about a 2mm gap between magnet and sensor (you can epoxy around both the sensor and magnet later for a more secure hold if you feel it is nescessary).

    Step 6: Once you've mounted the magnet on the Jackshaft output sprocket and the pickup sensor on the Jackshaft metal plate, you'll need to input a wheel circumference into the computer speedo of exactly 1162mm and have it reading the measurement in kilometers.

    Now you have a cheap and reliable Tacho which also stores highest RPM by scrolling to the "MAX SPEED" function and average RPM by scrolling to the "AVERAGE SPEED" function.
    Just some additional info on the obvious, but if it isn't - 18 kilometers per hour (KMH) = 1800 rpm, 22.7 KMH = 2270 rpm, 34.3 KMH = 3430 rpm.
    Naturally, "MAX SPEED" and "AVERAGE SPEED" reads the same way.

    This method works on any of the available Jackshaft output sprocket sizes because the sensor pickup is reading revolutions, not circumference - just mount the magnet on the sprocket and you'll be a happy chappy.

    Enjoy having a cheap tacho on your bike.

    For extra fuel capacity, i've installed a seat mounted drink bottle holder, using o-ring sealed aluminium drink containers - I use these for fuel, giving me an extra 1.5 litres of reserve capacity.

    Cheers Fabian

    Attached Files:

    Last edited: Sep 30, 2009

  2. EnFlaMEd

    EnFlaMEd Member

    Clever idea mate :D So you glued the magnet to the jackshaft sproket?
  3. Fabian

    Fabian Well-Known Member

    yes, exactly, held in place with superglue (cyano).

    I've found (so long as surfaces are spotlessly clean) that superglue has unbelievable holding power and sticks things in place forever.

  4. motorpsycho

    motorpsycho Active Member

    so this is a battery operated speedo that you can buy at k-mart?
    i have a battery operated speedo / multi function bike computer and it will not work on my bike when the engine is running.
    i tried MANY things to make it work, but so far nothing has cured the problem.
    does yours actually work when the motor is running?
  5. Fabian

    Fabian Well-Known Member

    Hi motorpsycho

    Remember the title - Motorised Bicycle Tacho - Super Simple & low cost

    Go to K-mart and buy yourself a Huffy 9 function bicycle speedo (it comes with a battery) and follow my instructions.
    Both of your bicycle speedos (the tacho speedo and the actual speedo, speedo) will work perfectly.

  6. motorpsycho

    motorpsycho Active Member

    well, the speedo/tach that i have is a 9 function as well, and it runs off of a watch type battery (a flat battery). it has a sensor that goes on the forks, and a magnetic pickup that goes on one of the spokes. This speedo works great with out the motor running. as soon as i start the motor, it locks up & resets itself. It's like there is a magnetic field around my bike when the motor is running. I have installed a shielded spark plug wire, which didn't help. if i totally disconnect the entire unit from my bike, hold it in my hands while sitting on the bike with the engine running, it still locks up and re-sets. Mine does not even have to be in contact with the bike for it to freeze with the motor running. This is the same type of speedo that you can buy at k-mart. this is why i was asking if yours works. i am thinking that maybe there is a problem with the ignition system on my motor, or that there is a grounding issue.
    all i know is that i tried a bunch of different things to try and get mine to work, and nothing has worked so far.
    i'm not worried about the tach function...i just want the speedo to work.
  7. Fabian

    Fabian Well-Known Member

    Yes, i had this exact same problem with the first 9 function huffy speedo - i would just go into reset mode after it came out of sleep mode but it never reset whilst the motor was running - i returned the speedo, got a replacement and it worked perfectly.
    The second speedo that i purchased also works perfectly.

    If you are having problems with yours, return it and get a replacement.
    My personal feeling is that it has nothing to do with emr and everything to do with the pickup points between the two pins at the computer base and the computer head itself.
    If they do not connect properly or vibration is causing them to momentarily loose contact, the computer may keep going into reset mode.
    The other thing that gave me problems when i first started using the speedo was not correctly seating the battery in the battery recepticle and not screwing the battery cover on tightly enough - check that you do this step correctly.

    Just return the speedo and get a replacement if it still doesn't work after going through those steps.

    Last edited: Sep 30, 2009
  8. Fabian

    Fabian Well-Known Member

    Anyway, this thread is about utilising a bike speedo for a cheap tacho.

  9. MikeJ

    MikeJ Member

    Hi Fabian -

    That idea of yours is so dog-gone slick! I nominate you for the Most Imaginative Product of The Year Award!

  10. Fabian

    Fabian Well-Known Member

    Hi MikeJ

    I was sitting down thinking about modifing my jackshaft chain tensioner with a ball bearing race and "BAM" the idea came to me about creating a super simple bicycle tacho.

    I went straight down to K-mart, bought a secondary speedo, walked into the electronics shop and asked for a pair of scissors, cut open the packet, cut the speedo wire in half (to strange looks from the shop staff) bought two lengths of 1 meter fine wire and heat shrink tubing; then walked into the local bicycle shop and bought the accessory extension hanger - total cost of about $25 for the speedo and heat shrink tubing and a few clips for another project and $30 for the extention hanger which i needed for the speedometer speedo anyway.

    After i got home and half an hour later (and after a few maths calculations), the setup was on my bike and fully operational.

    Now that is definition for a super simple and low cost tacho - to say i was happy with the result was an understatement considering the cost of professionally designed tachos and some of them don't have a max rpm and average rpm function.

    Cheers Fabian
    Last edited: Sep 30, 2009
  11. speedracer831

    speedracer831 Member

    well... good idea but there are mini tachometers that go up to 20,000 rpm for 2 strokes which only cost 30 bucks. so.. thats a little bit of work to do the bike speedo thing, ill just be lazy and get a real tach- which by the way is incredibly simple for install, just wrap the little tach wire around the sparkplug wire and there ya go!
  12. Fabian

    Fabian Well-Known Member

    Hi speedracer831

    Does the $30 tacho hold max rpm and average rpm figures and does it double as a spare pushbike speedo if one of them fails - where i live (Melbourne, Australia) the police will even give a person riding a bicycle a speeding ticket for travelling 3 kilometers (2 miles an hour) over the speed limit, particularly during school times when all the mums are dropping off and picking up their kids.

    In Melbourne, we have the most ridiculous and overly policed speed limits in the world.
    I have to watch my speed even riding my pushbike; having a spare speedo is essential.

  13. speedracer831

    speedracer831 Member

    wow they give tickets to bicyclists? in the US the only way you can get a ticket on a bike is running a light or crossing lanes- never for speeding. hmm. let me look at the website and let you know about what it does..
    here are the specifications for one type, cant remember where i saw the one that goes to 20,000 rpm.

    Simple hour meter with tachomter.
    RPM to 9,990.
    Option available to reset the hour meter.
    Different models for different engine types.
    Updates every 2.5 seconds.
    Standard wire length is 6 feet. Allow 2-3 weeks for custom orders.
    Estimated battery life is 5+ years — not replaceable.
    One year warranty. Click here for warranty information.
  14. speedracer831

    speedracer831 Member

    oh and its called a tiny tach, they are only 1.5" by 3" or 3.81cm by 7.62cm.
  15. Hawaii_Ed

    Hawaii_Ed Member

  16. Fabian

    Fabian Well-Known Member

    Hi Speedracer831

    Yes, they do give tickets to bicyclists - it's wrong, totally wrong but that's how the system works over here - they are totally and utterly mad.

    This specification is what i have a problem with: Updates every 2.5 seconds.
    If it updates every 2.5 seconds it's useless for a 2-stroke engine that's rapidly changing rpm's.
    It might be fine for a stationary diesel engine doing constant rpm's though, like a generator or water pump.

    Having said that, can you buy one of those tachos and have it record "max rpm" and "average rpm" all for $20.

  17. EnFlaMEd

    EnFlaMEd Member

    You can get done for DUI riding a dog on the road when your paro here in Australia.
  18. Fabian

    Fabian Well-Known Member

    Exactly EnFlaMEd

    People have lost their car licence for DUI on their roller skates, riding their horse, riding their bicycle, riding a childrens tricycle on the footpath, riding a skateboard and driving their boat and you could loose your licence for riding your dog - utterly mindless behaviour by the roads traffic authority and the police.

    How the heck can they connect these recreational devices and animals with a motorised and mechanised vehicle and how the heck can you loose your car licence for driving a boat on water - again - utterly mindless behaviour by the roads traffic authority and the police.

    Last edited: Oct 1, 2009
  19. Warner

    Warner Member

    That's what I was thinking...and what I have. Mount the little LCD meter to the handlebars, wrap the single wire around the spark plug wire, and you're done. Total install time under 10 minutes. The one I bought (from Staton) also doubles as an hour meter when the engine isn't running, so you know how many hours you have on your engine. The write up is CERTAINLY well thought out and innovative, but I'm not sure it's cost or time effective.

  20. Fabian

    Fabian Well-Known Member

    unless you have shops selling a useless single function tacho for $80 and up through to $250; not having the functions you want - that's what it's like living in Australia - everything is 3 to 5 times of the price of similar products in the U.S.
    If you can get an inductive style tacho for $20, then it's worth it if you are not interested in "max rpm" and "average rpm" recall.