Slot Car Corner - Making a Controller Adapter

Slot Car Corner

Adding Variables Brakes to Your Controller

Introduction

If you currently use a "basic", no-frills 1/32 slot car controller, here's a project which is just for you. By "basic" I am referring to controllers without adjustments for sensitivity or braking. Some of the more popular controllers which fall into this category are the entry-level Parma (tm) and Professor Motor (tm) controllers. Adding a variable braking adjustment makes it possible to "dial in" your controller to match your driving style, the characteristics of a given car (e.g. magnet/no magnet, motor braking) and track/lane conditions. Virtually all high-end controllers include a variable braking adjustment feature for these reasons. This article provides illustrated step-by-step instructions to add a variable braking adjustment to your controller.

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Step-by-Step Instructions

The picture to the right shows the basic components needed to add a variable braking adjustment to your controller. To assemble the components, you'll need a soldering iron (with stand and cleaning sponge), rosin core solder, rosin flux, a small brush, a wire cutter/stripper, some "helping hands", a drill (preferably a drill press), some sharp drill bits, painter's tape, and a heat gun (a hair dryer can also be used).

*** Important *** Always wear safety glasses and follow all manufacturer's instructions and safety guidelines when using tools.

Note: The components shown are available in kit form in the Online Store. If you prefer, pre-assembled variable braking kits are also available for purchase.

The first step is to drill a hole in the plastic box to mount the potentiometer (often referred to as a "pot"). I prefer to mount the "pot" to the bottom of the plastic box rather than the cover for a couple of reasons. First, the bottom of the box is a little sturdier. Second, assembly of the pot and wiring will be easier. Mark the center of the bottom side of the small plastic enclosure - a small piece of painters tape makes it easier to see the mark.

Now drill a hole centered on the mark drawn in the previous step. If you are using the potentiometer included in my kit, the hole should be 3/8" in diameter. If you are using a different potentiometer, use a drill guide to determine the diameter of the threaded mounting bushing.

*** Caution *** Use EXTREME care when drilling holes in plastic. Because the plastic is relatively "soft", the drill bit will have a tendency to "grab" the plastic and spin the box dangerously. Use a simple jig like the one shown in the leftmost picture to secure the box when drilling. A drill press should be used instead of a handheld drill if available.

Now mark and drill two (2) holes in opposite sides of the plastic box. The size of the holes will depend on the gauge wire you are using. For my kits with 16 gauge wire, drill 1/8" diameter holes. For kits with 14 gauge wire, drill 3/16" diameter holes.Now mark and drill two (2) 1/8" diameter holes. Note the hole is centered on the horizontal axis but below the center of the vertical axis. This will make it easier to secure the wires running inside the box in a later step.

*** Caution *** Use EXTREME care when drilling holes in plastic. Because the plastic is relatively "soft", the drill bit will have a tendency to "grab" the plastic and spin the box dangerously if it is not held securely. Use a simple jig to secure the box when drilling. A drill press should be used instead of a handheld drill if available.

The picture at the right shows the plastic box after drilling the larger hole to mount the potentiometer and the smaller holes (2 total - 1 visible in center of picture) to run our wires in a later step.

Before proceeding, let's take a closer look at the potentiometer. Notice there are three (3) tabs. When you wire up the potentiometer, you will only use two (2) of the tabs. So the question is, "Does it matter which 2 tabs?". Yes! You will always connect 1 wire to the center tab. Which of the "outside" tabs you use will depend on how you want the variable braking to work when you turn the potentiometer shaft. The leftmost picture shows how to wire the potentiometer if you want less braking effect when the shaft is turned counterclockwise. The rightmost picture shows how to wire the potentiometer if you want less braking effect when the shaft is turned clockwise. The article will wire the potentiometer using the picture on the left - this is consistent with how potentiometers behave in many everyday electrical devices and appliances (e.g. the volume control on your car stereo).

Before mounting the potentiometer into the project box, there are a couple of items to take care of. First, carefully bend the tab which will not be used out of the way as shown.

Next, use a sturdy pair of cutting pliers to carefully cut off the small tab which will prevent the potentiometer from sitting flush against the bottom of the project box.

*** Caution *** Make sure you are wearing safety glasses!

Mount the potentiometer in the bottom of the project box as shown - be sure the 2 sides of the box with the small holes are on the left and right (9 o'clock and 3 o'clock respectively in the picture) with the potentiometer oriented as shown. Hold the potentiometer in position while securing with the retaining nut on the bottom of the box as shown.

Once the retaining nut is hand tight, use an open end wrench to snug the nut in place. Be sure to hold the potentiometer in place and use care not to over tighten the nut.

You will need two (2) lengths of wire 6" long each. If you are using the wire supplied in my kit, simply cut it in half using some wire cutting pliers as shown.

Strip about 5/16" of insulation from one end of each wire as shown.

Insert one of the wires through the hole on the "right" side of the plastic box as shown.

Insert the bare wire through the small hole in the rightmost tab of the potentiometer as shown. Adjust the wire so there is a smooth bend/curve as shown.

Apply some liquid flux to the wire and tab as shown using a small brush.

Solder the wire to the tab on the potentiometer as shown.

Now insert the second wire from through the hole in the "left" side of the plastic box and repeat the same steps described above to connect the wire to the center tab on the potentiometer. The potentiometer and wires should look like the accompanying picture.

Use a pair of wire nippers to cutoff any excess wire protruding through the back side of the tabs.

Use a generous amount of hot glue to secure the potentiometer and wires to the inside of the project box as shown. The hot glue can be removed with minimal effort should it ever be necessary to replace the potentiometer.

Secure the cover to the plastic box using the screws provided. Use care not to over tighten the screws.

Slide the knob over the potentiometer shaft (you may have to loosen the retaining screw/s first) and secure by tightening the retaining screw(s) with a small screwdriver as shown. Be careful not to over tighten the screws or the "heads" may be damaged. The knob included with my kit has 2 screws - be sure to tighten them both.

Here's what the variable braking adjustment looks like at this point. Now all that remains is to connect it to the controller.

Use a pair of wire cutters to trim the two (2) wires coming out of the plastic box to about 2 1/2" long each.

Lay your controller wires on a flat work surface. Find the controller brake wire (usually red) and determine "where" you want to mount the variable braking adjustment box. I like to mount the box about 16" from the base of the controller; however, this is largely a matter of personal preference. Once you have determined where you want to mount the box, mark the controller brake wire as shown with some painter's tape. The section of controller wire between the 2 pieces of tape will be removed and replaced with the wires from the variable braking box.

Double-check the position of the variable brake box and cut out the section of wire from the controller braking lead as shown. Note there are four (4) wire ends - two (2) on the controller braking lead and two (2) on the variable braking box.

Strip about 5/16" of insulation from each of the four (4) wire ends as shown.

Apply a small amount of liquid flux to each of the four (4) wire ends and tin each wire end as shown.

Slide a short piece of heat shrink over the two (2) wire leads from the controller as shown. Make sure to keep the heat shrink away from the ends of the wire when they are soldered in the next step.

*** Important *** Make sure to perform this step before proceeding - you will not be able to slide the heat shrink over the wire once the butt connector is soldered in place in the next few steps. If you forget to put the heat shrink over the wire now, you will need to unsolder your butt connector to do so later.

Use butt connectors to join the first pair of wire ends (1 controller wire and 1 wire from the variable braking box). Use a small brush to apply liquid flux to the inside of the butt connector and to each of the tinned wire ends.

Soldering the butt connector will be much easier if you have both hands free. A pair of "helping hands" (available at many electronics or hobby stores) like the ones shown in the leftmost picture are worth their weight in gold for this type of task. If you don't have a pair of "helping hands", you'll need a helper to complete this step. Once the wires and butt connector have been positioned as shown, use the soldering iron to heat the butt connector. The butt connectors included with the kit have a small opening in the middle (see rightmost picture) - feed a small amount of solder into the joint through the opening. Let the butt connector cool for at least 30 seconds before removing from the helping hands to ensure the solder joint sets up properly. Repeat for the second pair of wires.

Slide the heat shrink over the butt connector and use a heat gun (or hair dryer set to the "High" position) to shrink in place as shown.

Run the other two (2) controller lead wires (typically the black and white wires) along the underside of plastic box. Use small tie wraps to secure the wires coming out of each end of the variable braking box to the other 2 controller lead wires as shown. Use additional tie wraps as needs to secure the 3 controller lead wires together.

The finished variable braking adjustment is now ready for use!!

Using the variable braking adjustment while racing is easy. While holding your controller with one hand, use your other hand to hold the variable controller box against your waist/hip area as shown. Use your thumb and forefinger to turn the knob clockwise (more braking) or counterclockwise (less braking). With practice you will be able to quickly dial-in the braking to match your driving style for a particular car and track/lane combination.

*** Caution *** Use care when hooking up your controller leads to your powerbase or driver's station. If you connect the controller leads incorrectly, you may damage the potentiometer and have to replace it. Replacement potentiometers can be purchased in the Online Store by clicking here.

Summary

There you have it - this is not a difficult project (prior experience soldering is helpful) which will only require about an hour of your time to complete. Variable brakes are a great addition to any controller - they will help you improve your driving skills by letting you quickly adapt your controller to a variety of cars and layouts.