Parts for the Speedo Car.
Bicycle Computer from any Bike Shop. The one below is from Ecowell.
Casula Hobbies K wagon that I assembled from a kit years ago.
Metal Wheel Set for the K: 23.8 mm long 10.5 mm diameter (36") - Steam Era Part No W4 or similar.
Magnet from the Wand supplied with Eureka Models sound locos.
- Mount the Sensor over the R/H Axle as shown in the Top photo.
- Cut Two Slots in the Sides of the K Wagon as shown.
- Carefully trim the Sensor's length with the Dremel as shown to eliminate too much overhang.
- Trim the sides of the Sensor.
- Drill a hole in the side of the Wagon to route the Sensor wiring back into the Wagon.
- I used a "square" Bike Computer as shown.
- If necessary cut a Slot in the Floor for the Bike Computer's Clip, so it sits rigidly, see below.
- I used a K&M Axle and ground a "flat" on the Axle to easily secure the Magnet, see below.
- Using your Dremel, trim the Magnet to 6.5 mm.
- Glue the Magnet to the Axle with 5 Minute Araldite and fit Axle to the Wagon.
- Trim the Sensor wiring for a neat fit.
- Before joining the wires, you have to CHECK the magnet/Sensor operation. Easier now.
- Connect the Sensor to a Multimeter, SET to OHMs.
- With the magnet "away" from the Floor, the Meter should show infinity (Open circuit).
- Rotate the Axle so the Magnet is CLOSE to the Floor, the Meter should show ZERO (short circuit).
- If the Sensor shows SHORT all the time, the Sensor will have to be RAISED above the floor.
- If the Sensor shows OPEN (infinity) all the time, the Sensor will have to LOWERED. Grind away the face of the Sensor and/or the floor.
- When the Sensor shows ZERO Ohms ONCE (close to the floor) in 360 degrees of Axle rotation, the Sensor and Magnet are set up correctly.
- Fit some 3.0 mm heat shrink to the two wires.
- Solder the connections then shrink the heat shrink.
Adjusting the Bicycle Computer for correct operation.
For the Bike Computer arrangement, the Computer will need to be programmed with a "multiplier" determined by the diameter of the Wheel to provide a "one pulse" per revolution signal. Counting these pulses over time time, the Computer displays KPH/MPH.
Since we modellers want scale KPH/MPH for our scenario and the Wheel of the K Wagon is a "scale" 36 inches in diameter, we use the SAME "Multiplier", as above.
Using the Instructions, you'll find a value close to the one I used in my original Speedo Car and what I programmed into my new Speedo Car. That is 2873.
You need to program your bike computer with is "2873".
To check your calibration:
- "Mark" 3 feet of straight track on your layout.
- Operate a loco at 10 MPH as indicated on the Speedo Car
- Using this 36 inch "Speed Trap", time the loco.
- It should take 18 seconds.
- If shorter/longer then you may need to change the "Multiplier".
- Don't be too pedantic here - close enough is good enough.
From the above, hopefully everything has worked out okay and you're ready to "Speed Match" your locos.
While I use 30 MPH for my maximum speed you can use what ever speed you desire.