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#710367 - 10/03/17 4:07 am Bicycle instruments  
Joined: Jan 2004
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DMadigan Online content
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DMadigan  Online Content
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ca, us
I had someone ask about wanting a small speedometer and tachometer for a project bike. The speedometer part was easy, a bicycle unit (Sigma makes one with a back light). The tachometer took some thinking.
An engine turning 1000 RPM makes one revolution every 0.06 seconds.
At 10 MPH a vehicle travels 8.8 feet/second.
If a wheel of 8.8 feet in circumference turned one revolution in one second a bicycle speedometer would read 10 (MPH). But if the speedometer was calibrated so each pulse from the wheel was in 0.6 seconds to read 10 MPH the pulses from the crank could be divided by ten to read RPM. So back calculating, the wheel would be 8.8 * 0.6 / PI * 12 = 20.168 inches (512.27 mm) diameter or 1609 mm circumference. Most bicycle speedometers can be set for wheel circumference.
So, putting in 1609 as the calibration, a magnetic pickup on the crank to measure each revolution, a divide by 10 counter to feed the speedometer, it can be used as a tachometer reading hundreds of RPM.
A wired speedometer would be preferred. The crank pickup could be set near the generator rotor which would need an additional divide by 3 or 6 depending upon the pickup and amplifier. Using the engine sprocket teeth would need a divide by 28 which is not as convenient.
Sigma makes a motorcycle version with three digit output for those turning over 9,900 RPM.

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#710382 - 10/03/17 11:44 am Re: Bicycle instruments [Re: DMadigan]  
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AngloBike Online content
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UK Berks
Doesn't running the speedo off the engine mean that revving the bike while stationary means you get a reading and the gears do nothing?
Surely you need pickup from a wheel or gearbox output?
Measuring rpm could be via emf pulses from the HT

#710384 - 10/03/17 11:57 am Re: Bicycle instruments [Re: DMadigan]  
Joined: Dec 2004
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kommando Online content
kommando  Online Content


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Scotland
I read the post as the speedo acting as speedo is run off the front wheel, its the speedo acting as tacho is run off the engine.

#710386 - 10/03/17 12:12 pm Re: Bicycle instruments [Re: DMadigan]  
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Al Eckstadt Online content
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Al Eckstadt  Online Content
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Jordan, NY
There are a number of small speedos with tachs built-in. But I am thinking of using one of these - small engine hourmeter/tachometer - hourmeter/tach on amazon.
Weatherproof and digital readout should help with stuff like tuning carbs. It's not backlit but then it only needs one small wire coil around an ignition cable.
[Linked Image]


Al Eckstadt
#710399 - 10/03/17 3:16 pm Re: Bicycle instruments [Re: DMadigan]  
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Hillbilly bike Online content
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Hillbilly bike  Online Content
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Running from demons in WNY
I tried one of those small engine tachs similar to shown above for the race bike. It was just for tuning purposes... The reading lagged behind actual engine RPM and was never stable...That was my experience, yours may differ....


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#710403 - 10/03/17 3:26 pm Re: Bicycle instruments [Re: DMadigan]  
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Al Eckstadt Online content
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Al Eckstadt  Online Content
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Jordan, NY
Thanks Tony. I'll investigate further before using.


Al Eckstadt
#710758 - 10/07/17 2:50 am Re: Bicycle instruments [Re: DMadigan]  
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Mark Z Online content
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Mark Z  Online Content
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I had a Sigma bicycle speedometer on my BSA for a while. The problem I experienced is that the sensor (which is actually a magnetic switch and not a pickup as in the sense of a coil, and therefore has a moving part) cannot stand up to the frequency of switching at 60-70 mph for very long. I went through two of them, each one lasting a couple of months.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
#710767 - 10/07/17 5:52 am Re: Bicycle instruments [Re: DMadigan]  
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NickL Online content
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NickL  Online Content
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Aus
If you want to use an analogue type meter....
http://www.ti.com/lit/an/snaa088/snaa088.pdf

Or just set up a row of comparators or op-amps and use leds Even a bar-driver.
Capacitor couple the coil for an input etc.

Why make it difficult????


Forget the bloody one's and zero's.
Old fashioned analogue engineer.

Last edited by NickL; 10/07/17 6:00 am.


#710787 - 10/07/17 1:19 pm Re: Bicycle instruments [Re: NickL]  
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Hillbilly bike Online content
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Hillbilly bike  Online Content
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Running from demons in WNY
Nice info Nick, but most guys here have trouble wiring a tail light wink grin


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#710791 - 10/07/17 2:21 pm Re: Bicycle instruments [Re: Hillbilly bike]  
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triton thrasher Online content
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triton thrasher  Online Content
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scotland
Originally Posted by Hillbilly bike
I tried one of those small engine tachs similar to shown above for the race bike. It was just for tuning purposes... The reading lagged behind actual engine RPM and was never stable...That was my experience, yours may differ....


I use this sort of thing.

http://www.eBay.co.uk/itm/Digital-E...4?hash=item41cd394f94:g:lgsAAOSw8DNZlxRo

It does get erratic. You have to experiment with numbers of turns of wire and mess about like that. I don't race, so it doesn't matter so much.

These GPS speedos are amazing (to me).

https://www.eBay.co.uk/i/1525967616...428-41853-0%2526rvr_id%253D1329369971191
[Linked Image]

I've got a similar one on the bike and it does work. Hope it keeps working!


Amateur Loctite enthusiast.
#710797 - 10/07/17 4:10 pm Re: Bicycle instruments [Re: DMadigan]  
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DMadigan Online content
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DMadigan  Online Content
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Mark, you should use a solid state Hall effect switch. They are not affected by the vibration or switching speed.
A digital tachometer is not much use on the road. It cannot be read easily in your peripheral vision. I bought some stepper motors GM uses for their instruments to play with. Debating whether to make original style instruments or a small all-in-one analogue tachometer with digital speedometer, shift light, multi-colour oil light, beam(?) and two line digital readout for miles/trip/time, maybe a turn light too. Just the essentials.
$miths already makes original style instruments so other than for my own use, not much need there. Back in the day, racers used Krober tachometers which have a 90 degree movement. Of course, no need to start from zero as that is pretty useless. If you have seen the recent Kenny Roberts video of him riding the TZ around a track, the tachometer starts somewhere around 6K RPM.

#710800 - 10/07/17 4:36 pm Re: Bicycle instruments [Re: DMadigan]  
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Andy Higham Online content
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Andy Higham  Online Content
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Bolton Lancs UK
I use a Scitsu tacho on my Greeves, it is rechargable and just has a sensing wire cable tied to the HT lead.
An unexpected advantage I found was when I was experiencing a misfire due to fuelling issues, the tacho was dropping back to zero indicating a low HT voltage=fouled / shorted plug=very rich
http://www.scitsu.com


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#710802 - 10/07/17 4:41 pm Re: Bicycle instruments [Re: DMadigan]  
Joined: Aug 2001
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Mark Z Online content
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Mark Z  Online Content
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Posts: 4,189
Owego, NY, USA
Yes, I only posted that because someone mentioned Sigma bicycle meters, and I was messing with them because they're cheaper than dirt.

My next attempt at a gauge was an electronic tachometer from Speedhut. This works great when it works, but it keeps failing. It has a lifetime warrantee, so I keep sending it back for repair, but I'm about ready to write it off and go for a GPS speedometer.

The Smiths electronic gauges are a little too pricey for me and my bitsa.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.

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