Northern Tablelands Express approaching Ardglen Tunnel

Northern Tablelands Express approaching Ardglen Tunnel
Click on the above photo to see the Main North Album at Flickr

Saturday, July 4, 2015

Speedo Car for Speed Matching Locos.

The most popular post on my Blog is my "30 MPH Max Speed Matching of all of my Locos", done in July 2010 with reference to my web page for making a Speedo Car. I recently made a Speedo Car for another modeller and I took some photos. Using these photos and the associated text you can make a Speedo Car for about $30 using one of your existing pieces of rolling stock.
Having a Speedo Car makes "speed matching" locos really easy.

An alternative to making the Speedo Car, purchase a module like the Train Speed 1 from TCS. See Ken Patterson's "What's Neat" series video, showing how he installed his TCS Speedometer

Parts for the Speedo Car.
Bicycle Computer from any Bike Shop. The one below is from Ecowell.
Casula Hobbies K wagon or similar. I assembled one 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.Your Wagon may be different, please check.
Magnet . I used the Wand supplied with Eureka Models sound locos and trimmed it to 6.5 mm see text.

Notes in Red added on 3APR2019.
  1. Mount the Sensor over the R/H Axle as shown in the Top photo.
  2. Cut Two Slots in the Sides of the K Wagon as shown.
  3. Carefully trim the Sensor's length with the Dremel as shown to eliminate too much overhang.
  4. Trim the sides of the Sensor.
  5. Drill a hole in the side of the Wagon to route the Sensor wiring back into the Wagon.
  6. I used a "square" Bike Computer as shown. Nov 2021, I used a $49 Ecowell BC10. 
  7. If necessary cut a Slot in the Floor for the Bike Computer's Clip, so it sits rigidly, see below.
  8. I used a K and M Axle with 10.3 mm Wheels and ground a "flat" on the Axle to easily secure the Magnet, see below.
  9. Using your Dremel, trim the Wand Magnet to 6.5 mm. DO NOT make it any longer. I made a 10.0 mm Magnet from a Wand and it DID NOT work with the Echowell BRI 8.
  10. Glue the Magnet to the Axle with 5 Minute Araldite and fit Axle to the Wagon.
  11. Trim the Sensor wiring for a neat fit.
  12. Before joining the wires, you have to CHECK the magnet/Sensor operation. Easier now.
  13. Connect the Sensor to a Multimeter, SET to OHMs.
  14. With the magnet "away" from the Floor, the Meter should show infinity (Open circuit).
  15. Rotate the Axle so the Magnet is CLOSE to the Floor, the Meter should show ZERO (short circuit).
  16. If the Sensor shows SHORT all the time, the Sensor will have to be RAISED above the floor.
  17. 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.
  18. 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.
  19. Fit some 3.0 mm heat shrink to the two wires.
  20. Solder the connections then shrink the heat shrink. Note: The Echowell BRI 8 wiring is difficult to solder. The strands of the multi strand wire are covered with insulation. Use your Soldering Iron turned up to 450 degC to melt the insulation. Use the normal Temp setting to solder the wires together. 

Adjusting the Bicycle Computer for correct operation.

For the Bike Computer arrangement, the unit 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. For my Ecowell BC10, I again used "2873"  Check your individual Bike Computer Manual.

You need to program your bike computer with is "2873".

To check your calibration:
  1. "Mark" 3 feet of straight track on your layout.
  2. Operate a loco at 10 MPH as indicated on the Speedo Car
  3. Using this 36 inch "Speed Trap", time the loco.
  4. It should take 18 seconds.
  5. If shorter/longer then you may need to change the "Multiplier".
  6. Don't be too pedantic here - close enough is good enough.
For a good Speed Calculator see:

Scale Speed Calculator

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.


  1. I thought I knew a lot about electronics & dcc, well what a pleasant surprise with what you have accomplished. Congrats from Canada!

    1. Hi David Thanks for the message. I am an Electrician and have been interested in hobby electronics for nearly 50 years and am now retired that lets me get by including understanding DCC but not enough to make circuits of my own. I need others to help there. Keep looking here as I continue my journey in this great hobby. Regards Marcus.

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