A car to measure speed and distance

[TheJoat]

I finally converted my old flatcar into a scale speed and distance car.

I bought a cheap bicycle computer at Wal-Mart and created a swivel mount to hold it - this allows me to look at the speed and distance from either side of the car.

Once mounted, it's pretty easy to calibrate - there was already a setting for 26" wheels available.  I used a magnet that I got from Russ at TapPlastics - it's very small and incredibly strong.

It's pretty neat watching my Shay move at 4 mph.   I also found out it's .626 of a scale mile around my loop.

[Capt Bob Johnson]

Duh!   Where does the 26" wheel setting come into it?

[mhampton]

Duh!   Where does the 26" wheel setting come into it?

I don't know for sure, but my guess is that it's the scale diameter of the wheels on the car.

 

[ttrigg]

Duh!   Where does the 26" wheel setting come into it?

That speedometer uses a magnet attached to the bicycle tire to count revolutions to compute speed and distance.  

How does it work in the GRR world?  Easy, you just need to select the setting in the speedometer for the true (12 inch to the foot) size of the wheels on your car.  If your flatcar has wheels that scale out to 26 inches in real life, the select the 26 inch setting and you are in business.

[TheJoat]

Tom's right.   I happened to have 26" wheels from Sierra Valley on that flatcar.  

 The point is that this is a very inexpensive way to get scale speed and distance.

[altterrain]

Neat project Bruce!

 -Brian

[John Richards]

HMmmmm, It`s nice to see there are still some things for the younger generation to learn

from us old Farts!.

Great Work. 

[TheJoat]

Here's a bit more information. 

Basically, the bicycle speedometer consists of:
 

• a unit containing the battery and the display.
  
• a sensor that is typically mounted on the front wheel mount. A LONG wire connects this sensor to the computer.  (I ended up cutting the wire as it was WAY too long.)
  
• a magnet that attaches to the spokes, and triggers the sensor each time the wheel rotates 

When you setup a bicycle computer, you have to "tell" it how big your wheel is.   There's a table of values for about 8 or 10 common wheel diameters - and you enter this into the computer.   There's also a mathematical formula you can use for other diameters.

Well, in this case, I'm using 26" scale wheels from Sierra Valley, so I entered the value for 26" diameter wheels into the computer.

I mounted the sensor between the wheels.  I didn't use the supplied magnet as it was too large.  Russ had sent me some really tiny and really powerful magnets - about 1/4" diameter and I attached it to the back of the wheel. 

So, every time the wheel rotates, it triggers the sensor.   The computer thinks it is measuring a 26" wheel - so everything is already scaled.

That magnet is REALLY strong.  It kept picking up screws and washers off my workbench.  

This is more fun than I thought it would be.   It gives me a much better feel for the speed I'm actually going.

[ttrigg]

Bruce:
This is an excellent modification of existing goods to the world of GRR.  Good job and thanks for sharing.  The beautiful part of this is that it really is a simple (or rather not complex) method, no building of electronic parts and boards, no real complex formulas to worry about.  I know there was an article couple of years back on how to build a meter.  Lots of little pieces to get from radio shack scared me off of that one.  Your adaptation is "Me Proof".  Like my solar lights in my structures, a little cut and glue and I'm in business.  The funny part of this story is that I explain to about a dozen people each week how to hook it to their bike and never made the link to GRR.  Thanks again for sharing.