Tachymeter design

The picture I was looking at doesn't appear to have a pin 2 on SKT1.

That should be pin 1. Ooops. Steve

Sorry I hadn't realised you meant I could leave them out when you said ignore them.

AJH

On or around Tue, 25 Apr 2006 13:57:12 +0100, Ian Rawlings enlightened us thusly:

too big a magnet and you'll have an unbalanced propshaft...

I've got a slightly different requirement, which people here may have ideas on...

I need a very accurate odometer fitting to a vehicle (mine). I'm not sure how accurate car ones are, but I want 1% tolerance. I don't want a kit - I want someone to fit, calibrate and test it, and ideally give me some kind of certificate. I'm aware that the calibration will drift as the tyres wear etc...

Anyone know anyone who can do this?

So another wedge of metal on the other side, or alternatively drop the reed switch and use solid state like a sensible person ;-)

Blummie - is that actually possible without having one of those extra wheels on a frame at the back and only driving at I don't want

Talk to your local weights and measures bods, or the nice people from HMR&C. They will know who produces such equipment. Any GPS based system will be too far out IMO.

I was thinking of a propshaft-based transducer, then calibrated over a measured number of wheel revs (or on a rolling road or similar). Certified for x miles until tyres wear to a certain amount.

Definitely don't want a GPS-based system, 'cos that's what I'm testing!

On Tue, 25 Apr 2006 21:17:44 +0100, Tim Hobbs scribbled the following nonsense:

Terratrips can be set up fairly accurately IIRC, given that they are used on competition vehicles. Not sure about certificates though.

Would have thought Warren might know someone?

Failing that, see if the plod know anyone.

I had a quick google about for doppler radar systems that point at the ground, but got bored.

That's probably your best bet. The guys who do the NZ Police speedo calibrations will also provide the same service to anyone else - not much use to you being 12000 miles away but I expect there's someone similar in the UK.

Otherwise the people who calibrate taxicab meters normally have the technology to at least test the mileage covered and give you an indication of what the error is.

Incidentally, which of your vehicles do you want to fit this to? If it's the Navara (which IIRC has an electronic speedo) it should be easy to hook in to the signal wire for that with a pulse counter that can then be easily calibrated to show distance travelled.

Yep, it's going on the Navara. Part of the purchase rationale was a truck with plenty of room to fit 'toys'. The space under the back seat is filling up nicely....

On or around Tue, 25 Apr 2006 21:46:09 +0100, Tim Hobbs enlightened us thusly:

try taximeter types, too - they're mostly driven form the speedo cable and calibrated over a measured mile. Whether they do as well as 1% I don't know.

Yes that was my first thought, there used to be a company called something like RDS that fitted this kit to tractors so you could measure the wheelslip (wheelslip is a function of efficiency in getting traction into the ground). Too late for me to google now but integrate the velocity and you have distance.

AJH

Yes please Steve, I'd appreciate that - snipped-for-privacy@a1.REMOVE.com.au

That's why I had a peek at it, with the idea that if it's good enough to measure speed accurately enough for tractor applications then it should do the job. ISTR it being fitted as standard to some models.

Acceptable margin is 5 percent, most will get away with 8, 9 or (at a push - and if they're not too stroppy) 10 percent.

Not really that good for Tim (or taxi passengers!)

Ah ok. Here in NZ the rules are

On or around Wed, 26 Apr 2006 20:29:31 +0100, Mother enlightened us thusly:

ISTR the meter being potentially more accurate than that. worth asking the taximeter makers.