how does a tachomter work?

to my knowledge...

either

the cable drives a magnet
the magnet induces a current in a coil
the current operates the speedo needle
the needle deflections is proportional with the speed

or

it is digital and picks up pulses from a toothed somethink
the faster, the more pulses
the pulses are counted
the number of pulses is proportional to the speed (more accurate than the
above)

 

It cranks over nice and fast. Never had any sort of problem starting.

If it was a loose wire, I would have expected the needle to drop to zero.
It actually goes off the scale at the other end (past the redline).

 

If it is electronic, and it is jumping to double revs, I would suspect a

The bike appears to be running fine. I can't notice any difference in the
engine when the tacho problem shows itself. It doesn't appear to change
when stopped in traffic, so I wouldn't have thought it was an overheating
problem. It's a naked bike, so airflow shouldn't be a problem. (Being
winter, I can definately attest to that!)

Will do.

I don't have one, but I might try and track down a friend that does.

Thanks for that information. It sounds very promissing. The fact that it
doubles the revs makes me think you may be onto something.

Paul.

 

On Thu, 24 Jul 2003 14:12:10 UTC, "Knobdoodle"

} They're simpler than that.
} The "cable drives a magnet" ones have a simple magnetic-couple (Two
} magnets in close proximity; when one spins the other one wants to too)
} driving a needle on a coil-spring.

Two magnets would couple way too strongly. It's just one magnet
rotating
inside a ferro-magnetic can. The can gets 'pulled along' by the
rotating
magnet, until the pulling force balances that of a coil-spring. The
magnetic force on the can is linear with the magnetic flux change, and
hence with the magnet's revs.

--
// Rik Steenwinkel '85 R80ST Skippy bike
// Enschede '91 R100GS/PD The Great Unwashed
// Netherlands ('76 Honda CB250G Bouwpakketje)
// "Far away is only far away '90 K75C Kommutabike
// if you don't go there" '81 MZ TS250/1+LSW Badkuip

 

I read somewhere that speedo's and tacho's use 'stepper' motors.
i.e. electric motors that dont rotate fully when current is supplied, rather
they can move to a set position depending on the current.

Could be a load of bollocks, I suppose, too.
Yours in good faith,
Justin

 

"Justin" wrote

My experience with stepper motors is that they, well... step. i.e. rotate
part of a revolution each time a pulse is applied. Not hold their position
or move to a set position.

Theo

 

By measuring tachyons.
I think I saw it on Star Trek or something...


Postman Pat

 

Maybe IntactKneeslider has one in the lab that you could play
with?



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