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Maintenance of Professor Motor Controllers

I have had some feedback re the controller problems re the brake pots burning out.

Although I had cleaned the controllers a week or so before the problem it appears that the wiper pad may get contaminated with a conductive compound .

This can cause the voltage from the power side of the wiper pad to be contacted to the brake terminal.

Thus current flowing where it should not be.

I had been cleaning the wiper pad with Shellite on a cotton bud. Then I put a very small dot of the grease - the process recommended by Professor motor.

Ok so maybe something got on the wiper to cause the conduction. This may not even be visible as some lubricants can also conduct current.

So I suggest we cover all reach controllers with a plastic bag when not in use .

I strongly suggest that if you have a Professor Motor Controller it may be a good idea to service it before EACH race meeting .

Also purchase the correct grease as recommended by Professor Motor. This is called Super Lube and is in a grey tube available from Thunderbird Slot racing.

Thanks to those that sent the information in reply to my email. I am happy to say though the controller performs well with the Pots as used by Diffalco.

Of course the controllers still have to be serviced as above

So be warned that servicing alone may not solve the problem . Best t keep checking the controller is nit heating up in the front top corner ( that’s 50mm away from the pots )

If the controller is hot it is best to disconnect & try a service before more damage is done. It is not a good idea to leave the PM controller connected to the track when not in use .

Peter D. Has sent this info he found on Professor Motor website. I am not sure if this information is included in the controller directions as its a while since I red the directions .

Hi John , Found this on the Professor motor Site

Use & Care Instructions


Caution ! : Regular maintenance is required

to keep the controller contacts clean and free from foreign objects & debris.

Failure to properly clean, lube and maintain the contacts will

cause the controller to fail, will allow the car to be driven

without the throttle being depressed and can result in the wire wound pot used for brake control becoming short

circuited & damaged. Please take this warning seriously

and follow this process to keep the contacts clean & properly lubricated :

Hope this helps. Peter D.

Also Chris in Melbourne was kind enough to give this explanation

The fact that the cars move slowly tells me a bit more, I don't have a professor

motor circuit diagram but the way tracks are normally wired up this tells

me that there is a stray positive somewhere on the trigger or the trigger

wire which would make the cars move and heat up the brake pots when at rest.

It is not the full track voltage so that is why it takes a while for the

brake pot to heat up, the type of pots normally used in this application

are usually rated in milliamps and not normally rated for 12 volts which

is not usually a problem in the brake circuit, the Difalco pot must be a

higher rating



I hope this has been an education in controllers for us . So hopefully with the maintenance recommended the Professor Motor controllers will continue to operate correctly

Another thing to watch out for with the Professor Motor controllers below:


For a while some people have been having problems with the Blue track controller being intermittent . I took it apart to service it yesterday.

I checked the wiper contact and all the usual service points.

I then notice a bit of a “knoble “ on one of the track connection wires. This was where the wire entered the controller. So in stretching the wire I could see it looking as if the center conductor was broken . On further stretching the insulation broke as the copper core had already broken . So here in was cause of intermittent power I thought. The insulation was holding the inner core together - sometimes.

I examination I found the other two wires to the track plug were the same . I could not believe the controller was still working - most of the time.

The wire used in this controller was the one with blue silicon insulation . The core wire is fairly fine in gauge compared to auto 4 mm cable.

So something else to inspect on your controller . I have has some of the plastic insulated wire brake in the same position.

Cheers, John

Fitting a larger Potentiometer to a PM Control - 1

Fitting a larger Potentiometer to a PM Control - 2

Fitting a larger Potentiometer to a PM Control - 3

Brake Pot conversion for Professor Motor Controller

Hi, sometimes good can come from disaster. I decided to attempt to replace the faulty brake pot in the track Professor Motor controller.

I had received some spare Brake/ Sensitivity pots in a special order from Aztronic in Sturt Street in Adelaide.

They were supplied after taking my Diffalco to them to get details off the pots on the controller. They were all 25 ohm .

The Part # is GTS 026 TB 32R 250B 1A1 1318Z

The fitting is very easy . Also you have to locate the 3 coloured flexible fly leads - heavy motor wires are good.

Also 2 fibre or similar washers to fit over the pot mounting shaft.

Thats all the parts 

You will need a soldering iron, solder & some knowledge of how to solder. and a spanner to fit the pot nut.

You will need another Knob for the pot as the shaft is bigger on the replacement pot.

This operation is designed to replace a damaged pot but I there is a benefit of better brakes and easier access to then brake control while driving.This could be worth doing whether the pot is cooked or not .

I have not replaced the sensitivity pot but I believe the same method can be used and it will fit near the original pot position.

Cheers, John

This is an alternate way to wire up the larger pot - without cleaning out the circuit board holes for the replacement pot wires. See the above pictures if you intend drilling the circuit board.

Professor Motor Controllers

The Track Controllers at FPR are all the Proffessor Motor Brand.

I have fitted 2 of the 25 ohm variable resistors (pots) to the controllers.

These are available as a kit from Professor Motor.

The "pot" allows the brakes to be varied from full brakes ( full clock wise ) to no

brakes about 1/2 a turn anticlockwise from the full brake position .

The other pot is fitted to vary the rate of acceleration and is called sensitivity.

. Fully clockwise is the less sensitive position. the car accelerates slower but it makes

the control of the car better in a lot of cases particularly the higher powered models.

Turning the sensitivity anticlockwise will increase the rate of acceleration and is

necessary for lower power cars to get the maximum speed. Each car can benefit in performance and handling depending on the position of the

brake & sensitivity controls .

Please ensure you get a controller that is POSITIVELY WIRED to suit most wood track

wiring. Negative wired controllers are for plastic tracks like Scalextric, Carrera ,SCX,

Ninco The plastic tracks have to be rewired to suit the positively wired controller.

Standard Professor Motor positive wired controller is :

Professor Motor PMTR2116 "Club Racer" Electronic Controller

Two 25 ohm "pot" kits are required to be fitted to this controller

PMTR2042 Variable Brake Potentiometer 25 Ohm

Perhaps the best way may be to buy the complete controller with the pots fitted. Also it has a heat sink & a polarity led and can handle the 16D motors that draw more current than most other motors. Part # below

Professor Motor PMTR2111 "Club Racer PRO" Electronic Controller .

Maintenance involves cleaning the wiper plate & contact with Shellite and then apply a small amount of the correct lubrication. Part # below

Super Lube SL21010 Super-Lube PTFE GREASE (Teflon derivative) 

The SCP-1 controller

This is an excellent controller. it has infinite control adjustments of braking and the power application. As well when switched to Mode 2 it had a variable car power control. This great for driving higher powered cars on tight tracks.

It is a bit more prone to damage if dropped so the PM controllers are a better option for track controls . If treated with care the is the ultimate controller in my opinion. Some disable the direction change switches and lock the curve control switch in case switch is moved by accident at the wrong moment .

We bought the handle without cartridge and the separate 20A cartridge so we could run higher amperage motors

SLOT.IT HAND CONTROLLER SCP01f - Electronic No Cartridge


However if you only wish to run motors under 5 amp draw you could chose this controller. This is supplied with the cartridge for positive polarity.

SLOT.IT HAND CONTROLLER SCP01a - Electronic (+) Positive Wired

Manual downloads for the SCP-1 --

Make sure it is the positive wired version for wood tracks & commercial centers. Damage can be done to the wrong polarity control. 

Controller Plug wiring

 The controllers have a wiring standard . The Yellow or white wire is the power to the controller from the track power supply. This is fitted to the N terminal of the standard Australian power plug.

The Red wire is the Brake and this goes to the negative feed from the power supply to the left track rail (in the direction of car travel).

The black wire is the positive controlled power from the controller and goes to the right hand rail of the track lane ( in the direction of car travel ) .

The wire color codes can be confusing particularly using the black wire on the control for the positive power feed . Also using red going to the negative rail with the brake signal. ( red for stop can be used to remember connection).

This is the standard international color code for slot cars and has been for 40 years that I know.

Most use the track lane color for the wire going to the positive right hand rail from the controller plug terminal "E" . This can help to save some confusion - perhaps .

Most use a black wire for the negative wire from the power supply which goes directly to the left hand track rail (DOT) .Connected to this black wire is the wire from the "A" terminal of the controller plug . This wire is the red wire to the brake terminal in the controller. ( red for stop! - not positive power in this case ).

Track Wiring

The controller hook up would be the 3 pin Clipsal 240v houshold socket plug. The white or yellow wire from the controller is the power to the controller from the power supply - positive . this is hooked up to the N terminal of the plug. This supplies power to the hot end of the resistor in the control.

The power is then sent to the track via the wiper in the controller at the value selected by the trigger position. The wiper of the control is connected to the black wire coming out of the controller. This goes to the track via the the E (earth) terminal of the plug. it is then fed to the right side track rail - in the direction of travel of the car.

The third wire is from the brake contact in the controller. This is the red wire and goes via the A terminal of the track controller plug to the negative of the power supply which is also connected to the Left side rail of the track - in the direction of travel.

Build your Own Controller !

There are the details of how to build your own controller on the Documents page as a PDF download. It is on Page 3 . Thanks to Dennis for supplying the information. Here is link to Documents page Document


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