FC.Speed is a two-lane slot car speedometer. It measures the time each car takes to travel between two sensors set six feet apart, then shows the calculated speed for that lane. You can view the car's actual speed or its equivalent speed at a selected model scale. This guide covers sensor installation, lighting, scale selection, the displays, and troubleshooting.
Accurate sensor spacing and consistent light are the most important parts of a reliable installation.
Quick start
- For each lane, identify REF 1 by its longer cable and REF 2 by its shorter cable. Choose positions where the car will cross REF 1 first and REF 2 exactly 6 ft (1.83 m) later.
- Install the four sensors facing upward in 5 mm holes. Keep their faces about 0.5–1 mm below the track surface and secure the cables beneath the track.
- Connect the sensor assemblies and power the unit with all four sensors uncovered and receiving steady light.
- Use the button on the right side to select 1:64, 1:43, 1:32, 1:24, or 1:1. The selection briefly appears on the displays.
- Drive through REF 1 and then REF 2. The corresponding lane's display shows the result and holds it until that lane completes another valid measurement.
Get to know your FC.Speed
There is one speed display for each lane and a scale-selection button on the right side. Each lane uses two light-dependent resistor (LDR) sensors:
- REF 1: The first sensor the car crosses, connected to the longer sensor cable.
- REF 2: The second sensor the car crosses, connected to the shorter sensor cable.
The order of travel is REF 1 → 6 ft (1.83 m) → REF 2. The speed shown is the average speed over that measured section. It is not an instantaneous reading at REF 2. Three LEDs for the lane illuminate when a valid speed measurement is completed, then turn off after a short period. The result remains on that lane's display.
Choose a place on your track
Drag strip: Put REF 2 at the finish line and REF 1 six feet before it, in the direction of travel. This measures average speed through the final six feet of the run.
Circuit: A long straight is a useful place to compare how fast cars travel. Put REF 2 near the end of the straight and REF 1 six feet before it. Keep both sensors within a section where cars cross them in the correct order and where light remains consistent.
Measure the distance between the detection points of REF 1 and REF 2 in the same lane. A different spacing changes the calculated speed. If you cannot fit a complete six-foot section at the desired location, choose another section rather than installing the sensors closer together.
Install the four sensors
- Check beneath the proposed positions for rails, electrical connections, supports, and wiring before drilling.
- Drill a 5 mm hole at each position: REF 1 and REF 2 in lane 1, then REF 1 and REF 2 in lane 2.
- Fit each LDR with its light-sensitive face upward, approximately 0.5–1 mm recessed below the racing surface. It must not protrude into the path of the car or guide.
- Secure the sensor leads and cables beneath the track. Keep exposed leads away from powered rails.
- Before fixing everything permanently, pass a car over each sensor to confirm it will shade the sensor without touching it.
For more on positioning optical sensors, see How to Install a Slot Car Lap Counter Sensor. The six-foot spacing and REF 1/REF 2 order in this manual are specific to FC.Speed.
Lighting and startup calibration
FC.Speed uses ambient light. At power-on it reads the light reaching each sensor as a starting reference. Leave all four sensors uncovered during startup: move cars and hands away, and avoid casting shadows across them. A car passing overhead briefly reduces the light and becomes a detection event.
Normal, steady room or track lighting is generally suitable. Deep shadows, moving shadows from people, or changing lamps can make detection less consistent. If lighting changes significantly, clear the sensors and restart the unit so it can establish a new reference. Keep the sensor faces clean.
Measure speed and choose a scale
Drive normally through both reference points. FC.Speed times the passage from REF 1 to REF 2 independently for each lane. After a valid pair of detections, that lane's three LEDs illuminate briefly and its display shows the speed. The displayed result stays in place until a new valid pass in that lane.
Press the button on the right side to move through 1:64 → 1:43 → 1:32 → 1:24 → 1:1. The selected scale appears briefly on the displays. Use the setting that matches your car when comparing scale-equivalent speeds.
- 1:1: The car's physical speed over the six-foot section, in MPH.
- 1:64, 1:43, 1:32, or 1:24: The corresponding scale-equivalent speed in MPH. These values express what that motion represents at full-size scale; the car itself does not physically travel at that displayed speed.
Use the same scale setting when comparing results. Scale selection changes how a measurement is expressed; it does not change the required physical spacing between the sensors.
Troubleshooting
A car passes but no new speed appears
Check that it crosses REF 1 before REF 2 in the same lane. Confirm both sensors receive steady light, are clean, and are shaded by the passing car. Check the sensor cable connections and restart with every sensor uncovered.
The reading seems too high or too low
Confirm the six-foot center-to-center detection distance in that lane and verify the selected scale. Use 1:1 to inspect the actual physical speed. An unexpectedly high number in a model-scale setting can simply be its full-size equivalent.
A display keeps showing an older result
This is expected until that lane completes another valid REF 1 to REF 2 pass. Check the sensor order and lighting if a newer pass did not replace it.
Readings become inconsistent after changing the lights
Restore steady lighting, clear all sensors, and restart so the unit can establish its reference under the new conditions. Avoid moving shadows across the measurement area.
One lane works and the other does not
Test each sensor in the affected lane, check its two connections and six-foot spacing, and confirm that cars actually shade both sensors. Compare its lighting and installation depth with the working lane.
Frequently asked questions
Does FC.Speed show top speed at the finish line?
It shows average speed across the final six feet when REF 2 is installed at the finish line. It does not measure instantaneous speed at a single point.
Can I install the sensors closer than six feet apart?
No. The calculated speed is based on a six-foot reference distance. Use that spacing for accurate results.
What does 1:1 mean?
It shows the actual physical speed of the slot car in MPH. The other settings show scale-equivalent MPH for their respective model scales.
Do I need FC.Platform to use FC.Speed?
No. FC.Speed displays measurements on its own. FC.Platform 2.0 does not currently provide an FC.Speed race or speed-data view.
Why do the LEDs go out while the speed stays visible?
The LEDs provide brief confirmation of a valid measurement. The display holds that lane's result so you can read it after the car has passed.
Care and support
Keep the sensors clean and unobstructed, secure their cables, and avoid pulling on the sensor leads. Before drilling or changing wiring, disconnect track power. If you need help, email fc.slotcars@gmail.com with your track scale, a photo showing both sensor positions and their spacing, the selected scale, and a short video of the pass.
Fernán Castillo
FC Slot-Cars