Build your own Omni Controller Click

Altogether too much emphasis is put on top end for winning races. Many variables involved in winning are more important than your motor's RPM. Body design, chassis design, center of gravity, low friction, driving skill, glue, weight, and proper combinations are but a few essential elements.

However, WHEN I PUNCH THE CONTROLLER I WANT ALL THE POWER THE TRACK HAS TO OFFER. I don't want to waste current on heating my controller wires, diodes, resistors or contacts. I want those electrons in the windings of my armature instantly when the hammer goes down. That's what a full power relay, or " click" does for you.

Before I tell you how to build one very inexpensively let's talk about the principle so you understand what you are doing.

The heart your click is an electro-mechanical device known as a relay. It is nothing more than an electrically controlled switch. You put current across two leads and it connects two others usually by means of an electro magnet. These gizmos come in all shapes and configurations depending on their purpose. They can be smaller than your motor brushes and control milliamp contacts or bigger than the room you are sitting in and able to cause a city wide black out. If you try to use a small device to control large current loads you will be left with nothing but smoke and if the relay you are using is too large it will be cumbersome and inefficient.


By choosing the right relay and connecting the control contacts to the ground and full power contact, and connecting the power circuit contacts to the black and white controller wires we have a basic "click". When the wiper hits the full power contact current goes across the relay control leads and connects the black and white power leads and sends full power to the track, bypassing the controller.

There remains however a few problems. Fortunately there are also simple solutions.

If your full power contact or band remains in your controller circuit it will find power and your "click" will be activated when you may not want it. This tends to bend cars. For this reason it is important to isolate the contact you choose to activate the relay. Depending on the type of controller you are using you may choose to use the last wiper band or the full power contact to control the relay. Using the full power contact tends to be simpler, the last band more reliable.

The last problem is a little nasty called "arcing". The details are unimportant but the solution is simple. For pennies at a local electronics supply house you will need to purchase a 150 ohm resistor and a small diode. Connecting these across the control leads of the relay eliminates the problem.

Now time to cut to the chase. How do I build this thing?

PARTS:
The relay you need is available at any automotive supply. Just go to the parts desk and ask for a 12V "fog lamp relay". Bosch and Blazer are two common brands. These carry 30-40 amps without a problem and shouldn't cost more than 3 bucks.

Next pick up your 150 ohm resistor and small diode at the local electronics shop. While you are there get a real small project box to enclose the whole thing. This prevents shorting out the track contacts by accident. A few feet of "hook up wire" is also needed unless you have a little lamp cord at home. Total cost: about 3 bucks.

And that is all the parts you need.

ASSEMBLY:
No matter what kind of controller you have assembly at the relay is identical so let's start there.

The automotive relays are meant to plug into a module, so have a standard configuration. They look something like this when viewed from the bottom:

And here is how you wire it:


A few practical points about wiring the relay.

  • notice the brake and power wires continue through the relay. Simply strip about 1/2" of insulation at the contact point rather than cutting the wire
  • twist the diode and resistor leads together prior to soldering
  • never use acid flux on electrical connections
  • place the whole contraption about 6" from the alligator clips

Now it's time to do the wiring at the controller end. How this is done depends on the type of controller you are using but the principle is the same. The control wire must be connected to an isolated full power point. Most controllers give you 2 points to use: The last wiper band and the full power contact point.

If you are using an INTERNAL RESISTOR CONTROLLER such as the Parma Turbo your choice is easy as it is not feasible to isolate the last winding of the resistor so you must use the full power contact. Simply disconnect any wires connected to this contact and attach the control wire from the relay. Chances are you disconnected the white wire which you must now connect to the full power end of the resistor.

EXTERNAL RESISTOR CONTROLLERS and SlotSide's personal favorite, the OMNI TURBO give you the option of connecting the control wire to the last wiper band or the full power contact. If you choose the full power contact the procedure is identcal to the internal resistor. Simply remove the white lead from the full power contact and replace it with the control wire. Be sure the white lead is still connected to the full power band on the wiper board and all other connections are removed from the full power contact and that it is isolated from the chassis of the controller.

If you choose to use the final band to control your relay then it is necessary to isolate it. In the case of the external resistor controller simply disconnect all wires from the final band and connect the control wire. Be sure the white wire is still connected to the full power contact. With the OMNI it is necessary to isolate the final band by cutting the silver conductor on the circuit board FRONT AND BACK with an exacto blade. This needs to be done between the brass conductor on the wiper board and the white wire. The white wire should be left in place.

A few words on using your new full power bypass relay.

  • Because the relay uses the brake lead as a ground wire, it is necessary to have your brake wire connected to the track for the click to be active. If you have a choke or variable brake, the device will still work.
  • If the bypass relay is working properly, you should be able to feel and hear it "click" when you punch the controller. If it clicks before full power, then you have probably failed to fully isolate the full power contact.

SlotSide would like to thank Carl Buchbinder of Cidex inc. for his help in preparing this article.


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