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A Simple Speedometer

by Neil (NHN)
This is a simple (as befits....) idea that came about from sheer curiosity regarding how far our little trains travel on their journeys.  I used to try counting laps of the L&L, but as I have the attention span of a teenager, that didn't work too well.  So the idea popped into the remains of my brain to use an electronic bicycle speedometer, as these are now freely available for not a lot - in this case, ten of our Manx pounds bought the cheapest one I could find, from the Raleigh brand.
The principle of these is simply (again....) a magnet that passes a sensor, and an electronic head unit that can be calibrated to suit different diameter wheels.  What I didn't know, is if it had sufficient range of calibration to cope with a 20mm diameter wheel rather than a 700mm one.  One way to find out.....
Installation was straightforward (you thought I was going to say simple again, didn't you!), using an Accucraft W&L open wagon, I have one which is used as a sort of GUV and is in most trains I run, as it has all the bits of coupling chains and other useful things in it!  I glued the magnet to one axle, although in fact the axle was steel and the magnet stuck to it pretty well of it's own accord, but I like a belt and braces approach.  I then glued the sensor under the floor of the wagon leaving a small air gap between it and the swing of the magnet.
Calibration was as described in the speedometer destructions, using a measured length of a known number of rotations or something, I forget now, but the instructions were straightforward enough to follow. A decision has to be made at this point as to whether you want the speedo to measure real MPH/distance, or scale....I opted for real, if you want scale, then the calibration distance factor has to be multiplied by your chosen one.....the value of which which can be a problem with garden trains!  Anyway, a couple of cable ties to neaten things up, I thought I would shorten the cable later if it worked (never bothered!) and off we went for a trial.  IT WORKS!
In the photo you can see it displaying 2.69 miles - real ones - this was the distance covered by one of my battery 'diesels' a fortnight ago, together with a 'two gas tank' run of my Mortimer - amazing isn't it, I never imagined that this sort of distance would be covered.  Last year, this little wagon travelled over 66 miles, you can see the plating has worn off the wheels in one shot (where the treads aren't covered with muck, anyway).
An interesting little device anyway, for the curious!
What I did find, as I suspected, is that many garden railway folk run their trains much too fast.....and then some.  I aim for about 0.7 mph, multiply this by whatever today's scale is, and you get scale speed.....15mph is, I think, line speed on the Tayllyn, as a forinstance.  This takes some doing with a lively (read my VoR) steamer.