Bike computer as tacho?

NickRobinson

NickRobinson

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Not wanting to hijack the 'Tinytach' thread ...

Who has successfully bodged, sorry modified, a bike speedo to give diesel engine revs onboard?

sticking on magnets, much faster pulse rate, wheel rim circumf. to revs calibration, etc...


Nick
 
NickRobinson said:
Who has successfully bodged, sorry modified, a bike speedo to give diesel engine revs onboard?
Click to expand...
Thought about it but not done it.
sticking on magnets, much faster pulse rate, wheel rim circumf. to revs calibration, etc...
Click to expand...
A magnet on the fly wheel shouldn't be a problem given clean surface and araldite, but it depends on the device, don't some use a reflective strip?

wheel rim circumf. to revs calibration won't be an issue as it is revolutions you are measuring and the outer rim rotates the same number of times a minute as the hub, you will be in trouble if it doesn't :D
 
wheel rim circumf. to revs calibration won't be an issue as it is revolutions you are measuring and the outer rim rotates the same number of times a minute as the hub, you will be in trouble if it doesn't :D[/QUOTE]

True, but the bike speedo doesn't display revs, it displays revs X piD/60/60?
(assuming circumf in miles or km)

Sunday's too much.. I'm teaching maffs all week!

N
 
NickRobinson said:
Not wanting to hijack the 'Tinytach' thread ...

Who has successfully bodged, sorry modified, a bike speedo to give diesel engine revs onboard?

sticking on magnets, much faster pulse rate, wheel rim circumf. to revs calibration, etc...


Nick
Click to expand...

There are different sites to be found how to do this.
http://www.instructables.com/id/Tachometer-made-from-a-bicycle-speedometer-cycloc/
A few years ago, I made the setup using a wireless bike speedometer and a powerful magnet, not on the engine, but on the propellor shaft (on the flexible coupling, actually). Worked fine, but only to a distance of max. one meter. Also, I remember the reading to be a bit odd, since indeed you measure revolutions, but most speedometers give distance travelled. There are now bike speedometers with a revolution function buried deep in the menu. The problem is to find a shop knowledgeable enough about the units they sell.
 
LadyInBed said:
OK, that is a bit of a problem!
Aren't there models that can measure cranking speed in RPM? This would be the function to use, if it can cope with you peddling at 4000 RPM :D
Click to expand...


Yes there are. They measure the "cadence" of the rider but they are usually only on the more expensive bike computers rather than the cheapie £7 ones from Lidl.

FWIW when I repaired my cycle computer I found that it was operated by a simple reed switch. So long as the engine speed isn't too fast for the reed switch it will probably be fine.

It won't be able to give you a "true" reading so you would probably need to set it that it read some thing like 22.0 mph when you want it show 2200 RPM but that's not really a problem.

The problem may be that you'll need a tachometer so that you can calibrate the thing!
 
Last edited:
NickRobinson said:
Not wanting to hijack the 'Tinytach' thread ...

Who has successfully bodged, sorry modified, a bike speedo to give diesel engine revs onboard?

sticking on magnets, much faster pulse rate, wheel rim circumf. to revs calibration, etc...


Nick
Click to expand...

THere was a YAPP project on here a few months ago for a rev counter for an outboard you could probably modify if you PM ANgusMcDoon.
 
A while back in PBO there a was piece on making your trailing log from a bike speed/distance kit. I bought the bit. The bubble wrapping is pretty yellow now when I notice it.
 
Thanks all respondents!

It could be a winter project...

I was half way through a walk near Kinder this afternoon when I realised my 60/60 made me out my a factor of 60.... (gives rps, not rpm...)

Amazed no one noticed... ;) or was too rude to post :o

Nick
 
EdBeynon said:
THere was a YAPP project on here a few months ago for a rev counter for an outboard you could probably modify if you PM ANgusMcDoon.
Click to expand...

I'll have a go. It will be simple to modify the YAPP-o-tach to use a magnet and Hall sensor instead of the HT lead induction method. I have already done a PID control of an electric motor using magnet/Hall, and the YAPP-o-tach can be modified simply to use that method of input. I will make the circuit diagram and software open source as usual. In fact if anyone wants me to, I could send them a flashed processor at cost price too.
 
Many years ago, an old engineer gave me a hand held tacho, for measuring shaft/wheel speeds.
Now at last I have a device that you can borrow to record the true rpm on your bike speedo
 
Would you believe I actually bought a £4 thing off ebay last week for this exact purpose.
Fitting it next weekend I think. I am putting it on the prop shaft as it spins at half the speed of the engine so might work better.
The only thing you have to do is set the correct "wheel circumference".
Most computers allow you to set the wheel circumference in mm so by my maths I worked out that if you set the units in km/h you could get 10.00 km/h = 1000rpm by the following:

10.00km/h = 0.166km/min = 166m/min = 16,666 cm/min = 166,666mm/min

1000rpm on engine = 500rpm on the shaft

166,666 / 500 = 333mm "wheel diameter"

Only problem I think is if the computer can't handle such a fast rpm. Other thing is that it wont work in neutral but thats fine.
 
I did it! I bought a bike computer off ebay, I think it cost about 5 quid. The one I bought did give rpm. I drilled and screwed on the magnet to the flywheel. The detector I connected to the front of the engine compartment. It worked sort of but the revs wouldn't go above 750rpm. Eventually the magnet hit the sensor and broke. I then chucked it into the bin.You'd need to check how fast it can go, 750rpm with an average size bike wheel would be about 90kph I needed it to go up to about 2000rpm which would be 270kph a fair bit faster than any bike. So you can get them that measure rpm but it may not be fast enough. Check out the specs first see how fast it can go and secure the sensor to the engine somewhere. I might try again its possible.

NickRobinson said:
Not wanting to hijack the 'Tinytach' thread ...

Who has successfully bodged, sorry modified, a bike speedo to give diesel engine revs onboard?

sticking on magnets, much faster pulse rate, wheel rim circumf. to revs calibration, etc...


Nick
Click to expand...
 
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