How can I build a variable speed controller for a slot c

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stevo1
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How can I build a variable speed controller for a slot c

Post by stevo1 » Tue Mar 29, 2005 5:01 am

Hi, Can anyone tell me the simplest way in the form of a turnable knob swich that I can vary the power to a slot car track so I can have a car running at a speed I choose and then race against it using a standard controller on the other track?
I have tried some volume/dimmer switches and have had them burn out almost immediatly.
The voltage is drawn from a standard Scalextric 15V transfromer and I believe there has in the past been commercially avalable "Ghost Car" varable controllers for this purpose.
I have little to no electronic experience but can do basic soldering.
Hope you can help.
Stevo.<p>[ March 30, 2005: Message edited by: stevo1 ]<p>[ March 30, 2005: Message edited by: stevo1 ]<p>[ March 30, 2005: Message edited by: stevo1 ]</p>

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dacflyer
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Re: How can I build a variable speed controller for a slot c

Post by dacflyer » Fri Apr 01, 2005 9:47 am

you cannot use a pot. or dimmer...what you need is a wire wound rheostat.. probably about 50 watts or more.. i have some here i think..
they are big and ceramic approx 3" wide..really heavy duty.. have to look in my boxes to see which ones i have.. got any spec. on the motor? like how many amps they draw at full load?

Mike
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Re: How can I build a variable speed controller for a slot c

Post by Mike » Fri Apr 01, 2005 3:52 pm

Slot cars are usually very tiny DC motors. Nothing big, the motor on mine is about an inch long, 1/2 inch tall, and 3/4 inch wide.

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haklesup
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Re: How can I build a variable speed controller for a slot c

Post by haklesup » Fri Apr 01, 2005 4:59 pm

you cant use a pot to control power or current like that. As you dial the wiper to the extreme position, the resistance goes to minimum value and the current goes to the maximum. When you do this you are using only a very small portion of the resistive element which has a fraction of the power dissibation of the whole element. increasing current and decreasing wattage equal smoke<p>If the car is an AC motor then the controller probably resembles a wire wound resistor but may be really a miniature AutoTransformer like a tiny Variac. The wiper is a variable center tap for the transformer and the output is across the wiper and one terminal while the input is across both end terminals. At least this is how I understood Train controllers.<p>If it is DC the best approach would be to use the Pot to control a variable DC supply. Though I am not familiar with how it is conventionally done for slot cars.<p>I'm thinking there is a way to wire the pot as a rheostat (shorting two of the terminals) but can't for the life of me work out the input and output right now

Intimidator#3
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Re: How can I build a variable speed controller for a slot c

Post by Intimidator#3 » Fri Apr 01, 2005 6:22 pm

stevo
If you have 2 transformers, run one to each lane(better that way so you dont get the spikes when one car comes off) an put the ghost car transformer on a light dimmer used in houses

Dean Huster
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Re: How can I build a variable speed controller for a slot c

Post by Dean Huster » Sat Apr 02, 2005 1:49 pm

I tried this back around 1966, replacing the rheostat control with one using a pot with a power transistor to handle the motor current. I was only a few years into electronics back then, so the design wasn't very sophisticated, but it worked.<p>Another facet of slot cars is that (at least with the one I dealt with) when you release the button, the controller shorts the tracks, effectively braking the car. I didn't have the knowledge back then to incorporate that feature into my solid state controller.<p>These days, I'd use a 555 timer driving a TIP120 for pulse-width control of the motor. Lots more efficient!<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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