I have finally managed to persuade the charming ladies at DVLA in Exeter to give me an age related plate and the bike is now road legal well nearly as I don't have a speedo fitted yet. I'm hoping to get an electronic chrono replica and have been measuring the drive ratio.

This works out at 17 rotations of the drive to 8 of the rear wheel - i.e. 2.125:1 which seems a rather strange value.

Any thoughts please?

Thanks,
Bernie

email (option): bernie.a.jones@gmail.com

Hi Bernie..The first problem you might have with an electronic speedo is finding one that functions on 6 volts...I think there's a Dutch guy makes them..Assuming there is something that will do the job the ones I have had any experience of fall into two categories...Some use a magnetic trigger and some work on the 'hall effect'..ie..they pick up on, for instance, holes drilled in a circular plate by measuring the variation in a magnetic field. I believe ABS sensors work using this principle.....Either way most of the ones I have seen have an electronic 'offset' facility to adjust the speed they are recording from the trigger or plate to suit the actual speed you are travelling at...In other words they can be calibrated once fitted. So in the final analysis the ratio of the original drive unit they are replacing becomes irrelevant...Ian

email (option): ian@wright52.plus.com

You probably meant Hans Beck, beckelektronika@planet.nl
He makes a speedo that fits inside the original housing and has an electronic pickup.Costs € 95.
Site is in Dutch, but Hans will reply in Enlish

email (option): viaconsu [at] planet [dot] nl

Hi Hans...What's Enlish?..Sounds like something from Lord of the Rings... ...Is the Dutch speedo completely electronic or does it still employ the cable drive as part of the system?...Ian

email (option): ian@wright52.plus.com

Yes Ian, my Enlish, I mean ENGLISH is deteriorating; old age, I suppose
And the speedo is completely electronic, including the cable!

email (option): viaconsu [at] planet [dot] nl

Thanks all - it is Hans Beck that I've been emailing and I've mentioned the 6V electrics so hope that will be OK. His design uses a sensor that screws onto the speedo drive and this is then wired to the speedo. I think that the electronics needs to be hard-wired to get close to the correct ratio and can then be finally calibrated in-situ using a trimmer.

I tried to build one myself a while back using a stepper motor and some programmable electronics to drive it. Calibrating was the most difficult part and as a stepper motor has no natural 'home position' it has to be programmed to perform a self-calibration sweep on every power up. I haven't persevered with the idea but believe that Hans uses mini servos as used in R/C models - which I think have their own internal positional feedback circuit - probably a much better idea than using steppers!

Cheers,
Bernie

email (option): bernie.a.jones@gmail.com

Say that again in Japanese Bernie... ...My Sportster has an electronic speedo that picks up it's signal from a sensor on 5th. gear in the gearbox..The speedo also incorporates electronic fault diagnosis and there is some sort of speed/distance gadget that works the self cancelling indicators....I don't really understand any of it and would happily throw it away if I understood how to get rid of it.....I still adhere to the old way of thinking that the whole point of a motorcycle is to have a simple form of personal transport...How out of date is that?.....My pals new Triumph has not one, but two computers to control all the gizmos and gadgets...and that isn't even the 'more complicated' touring model....
Beam me up Scottie... ....Ian

email (option): ian@wright52.plus.com

I agree Ian - the M21 is the first bike I've done with mag/dyno and it's a bonus to know that it will start and run without the need for any additional electrics. As I only plan to use it for pottering around the Dorset lanes and the occasional charity run I could manage without the speedo but suspect it's probably not quite legal!

Just got to get the transfers on and finish a couple of bits and pieces and I'll post some pics.

Cheers,
Bernie

email (option): bernie.a.jones@gmail.com

Hi Bernie..A cheapo digital bicycle speedo works fine and satisfies the legal requirement...They have sufficient 'range' of speed and the offset facility...Available both 'wired' and 'remote', powered by an ordinary dry cell or 'watch' type battery that lasts ages and they just mount to the handlebar with a pickup or sender on the wheel, dependant on type......Available fom most bicycle shops...and I noticed Tesco have them... Less than a Tenner for basic models...Ian

email (option): ian@wright52.plus.com