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r377

Professor Motor brake upgrade

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Hi,

 

Relatively new to hobby, i haven't done a brake pot upgrade before.  Is there much to it ?

 

I am struggling with brakes on my Professor Motor controller with 24 scale cars and more powerful motors.

 

The brake pot is marked 1417.  What sort of new part would you recommend and is there much to fitting it ?

 

thanks

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Howdy,

So you need to NOT use a resistor style controller, but rather a electronic unit.

Each motor will have different resistance, therefore different characteristics.

Mine..................

 

http://www.thirdeyetechnology.net/

Horrific prices, though !


...............Take it easy

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I think Roger miss read your question.
Brake pot problems on PM controllers often happen.

I assume you have full brakes and when you turn the brake knob you loose all brakes?

If so the resistor in the pot is broken, These pots are of a different physical size to normal pots and have a 1/8 shaft.

It is possible to fit a conventional wire would pot but much easier to just buy a replacement PM pot from Thunderbird. You only need to desolder the two pot connections on the board and fit the new pot.

Edited by kalbfellp
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Phil

 

Hobart Miniature Car Club

 

Tassie Resins

 

Email

 

 

 

 

 

 

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I agree with Phil.

I suffered (what I think is) the same problem ... all OK when using maximum brake  but 'free wheeling' as soon as I started to reduce brake.

My friendly neighborhood 'Phil' diagnosed the problem and replaced the pot  for me.

Den

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Thanks for the replies, that slot.it controller looks good, but heard they are hard to work on and repair ?

 

I just don't have enough brakes on certain motors, including revo.  Not sure if i didn't notice before and its gotten gradually worse.  I put the brakes on full and it just doesn't stop in time.  Still got decent brakes on my thunderslot.  Put brakes on min or half and its even worse.

 

Was looking at getting this brake pot ?

 

https://www.professormotor.com/product-p/pmtr2039.htm

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The brakes on the controller may not be the issue. Some cars brake differently to others due to a range of factors, such as gearing and magnets and the overall quality of the motor.

Which 1/24 cars are you running? Have a look at the gear ratio and do a search on here or other forum looking for gear ration and braking. 

A change in ratio can bring about a change in braking characteristics.

cheers

DM

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2 hours ago, dangermouse said:

The brakes on the controller may not be the issue. Some cars brake differently to others due to a range of factors, such as gearing and magnets and the overall quality of the motor.

Which 1/24 cars are you running? Have a look at the gear ratio and do a search on here or other forum looking for gear ration and braking. 

A change in ratio can bring about a change in braking characteristics.

cheers

DM

 

Thanks running stock revo it was struggling.  Also slot.it red flat AW12-28 and  22 shark 13-32  thanks

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Jaycar have some in stock which would be much cheaper

 

 

 

 

 

5k Ohm Logarithmic (A) Single Gang 24mm Potentiometer

CAT.NO:RP3608

With imperial standard shaft & bushings made to our rigid engineering specifications. The potentiometers are full size - 24mm diameter types . Power rating is 0.5W max. They have genuine 6.35mm (1/4) shafts with a flat machined 25% of the diameter for grubscrews or interference fit knob mounting. The shaft is a generous 38mm long. The bush is a 3/8 32 T.H.D. type which we believe is necessary for good fixing to a panel. Another important feature of the pots is their PCB mount capability. The pins are rigidly mounted on phenolic with the centre pin offset from the two outer terminals. When soldered into a PCB, the pot is quite rigidly held on its own. Double gangpots are held in 6 places and require no extra mechanical mounting assistance. The pins are large enough to terminate screened cable, etc., if the job requires hard wiring. An engineering drawing appears below. You may safely use it to design PCB artwork etc., as we have standardised this design.Value5K

5k Ohm Logarithmic (A) Single Gang 24mm Potentiometer

 

 

 

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5k Ohm Linear (B) Single Gang 16mm Potentiometer

CAT.NO:RP7508

 

These pots have imperial standard shaft.- Shaft is 1/4 D type (30% of shaft has been removed for flat), so they suit all our knob range.- Shaft length is 30mm, so there is plenty there if you need more length.- Power rating Linear 0.2W and Log 0.1W.Value5K

 

5k Ohm Linear (B) Single Gang 16mm Potentiometer

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5k Ohm Linear (B) Single Gang 24mm Potentiometer

CAT.NO:RP3508

 

With imperial standard shaft & bushings made to our rigid engineering specifications. The potentiometers are full size - 24mm diameter types . Power rating is 0.5W max. They have genuine 6.35mm (1/4) shafts with a flat machined 25% of the diameter for grubscrews or interference fit knob mounting. The shaft is a generous 38mm long. The bush is a 3/8 32 T.H.D. type which we believe is necessary for good fixing to a panel. Another important feature of the pots is their PCB mount capability. The pins are rigidly mounted on phenolic with the centre pin offset from the two outer terminals. When soldered into a PCB, the pot is quite rigidly held on its own. Double gangpots are held in 6 places and require no extra mechanical mounting assistance. The pins are large enough to terminate screened cable, etc., if the job requires hard wiring. An engineering drawing appears below. You may safely use it to design PCB artwork etc., as we have standardised this design.Value5K

 

 

5k Ohm Linear (B) Single Gang 24mm Potentiometer

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These pots from Jaycar are not suitable they are not wire wound.Also will not fit the circuit board. Brake pots are usually 5 or 10 ohm.

If the brake pot is on full brakes and you do not have enough brakes then the pot is not the problem.

Easy test is to bridge the two lugs on the pot and test.

The wiper may not be contacting the brake stop.

As DM mentioned braking is different from car to car.

 

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Phil

 

Hobart Miniature Car Club

 

Tassie Resins

 

Email

 

 

 

 

 

 

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Hi again r377,

I have four (4) Revoslot cars and haven't noticed any problems with the braking - excepting, of course, when the defective 'pot' was still fitted.

A few more questions come to mind :

Is anyone else having problems with the braking on your track? Have you tried using another controller? Have other people driven your cars with their controllers?

And as silly as it may sound, is the wiring on your track set up for braking? I can tell your that one of the tracks that I race on in my local area DID NOT have 'built-in' braking until the track-owner rewired the track earlier this year.

Den

 

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10 hours ago, big den said:

Hi again r377,

I have four (4) Revoslot cars and haven't noticed any problems with the braking - excepting, of course, when the defective 'pot' was still fitted.

A few more questions come to mind :

Is anyone else having problems with the braking on your track? Have you tried using another controller? Have other people driven your cars with their controllers?

And as silly as it may sound, is the wiring on your track set up for braking? I can tell your that one of the tracks that I race on in my local area DID NOT have 'built-in' braking until the track-owner rewired the track earlier this year.

Den

 

 

Good idea thanks for reply.  Yes, it might be more of different tracks and different cars.  I don't race heaps regularly enough to see this ongoing problem might take a while to work out.  Ill try more controllers and different tracks to try and work it out.

 

Pulled my controller apart last night and cleaned the brake pot, will see if its any better next time out..

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Just curious- what is the difference in wiring that makes a track "have brakes" or "not have brakes"?

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So........A Dc motor becomes a generator on the down run, eg coasting along.

Via the controller trigger, a contact is provided, that shorts out this power from coast down.

The Brake pot thing is placed in this circuit, providing variable amounts of flow path power, in layman's terms, to make it stop in shorter or longer distances.

 

You can see how a different power motor WILL provide different characteristics, in stopping and going as well.

Therefore I suggest going to an electronic controller for more consistent performance.


...............Take it easy

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On 7/3/2021 at 11:21 AM, Shaynus said:

Just curious- what is the difference in wiring that makes a track "have brakes" or "not have brakes"?

Hi Shayne,

The difference is exactly where (or if) the red wire (brake) is installed within the track wiring. When you release the trigger (hopefully) you activate what is known as 'dynamic braking' in which a reverse current is applied to the motor thus slowing it down. If the brake wire isn't installed in the correct position there isn't any dynamic braking and the car will just coast rather than brake. (as was the case at my local track until February this year).

The tracks I first ran at in the 1960s used a 2-pin connector for the controller to plug into, with a separate terminal that you could connect your 'loose' brake wire to for braking. The clever boys of that era quickly found out that by incorporating a 9-volt battery in series in the brake wire they could have 'power braking'.

The early Scalextric power supplies only had two terminals for connecting power to the track but with an after-market MRRC controller (or similar) you could have braking by connecting the third (brake) wire to one of those terminals.

Den

 

 

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It’s easy to wire in a pot to a Parma controller and they are cheap.

Of course you can go overboard. :D

240390428_1425146507872596_2237760113614

Edited by Sports Racer

May the downforce be with you.

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Funny guy Sports Racer - - - planning to do all your driving with that above ? :lol:

- r377, have you ever resolved the problem from back in June?
Do you know which model of controller do you have (All P.M. controllers are identified by a 4 digit model number)

By "upgrade" you really mean "repair" 
You can never get extra braking capacity by adding or changing the brake pot. They are there to provide a reduction in braking, by adding some resistance into the dead short circuit.
In other words, you can't upgrade braking to make it better than dead short.

Depending upon the model of your controller, and it's original purpose; the brake pot it will have been fitted with will be either of
PMTR2039   5 ohm wire-wound for commercial 1/24th racing
PMRT2042  25 ohm wire-wound for 1/32nd  RTR racing
See here

The product code 1417 doesn't gel with me.
So it MAY be a PMTR2039 5 ohm pot for 1/24th controllers,  it certainly isn't a 25 ohm PMTR 2042 as used in 1/32nd scale racing hard body controllers. They have quite different marking on the can.

ALL controllers start from that base position of dead short to the track at rest. So if you are lacking brakes compared to another controller, then you may have any of
- something is wrong with the existing brake pot which is possibly open circuit
- or the controller wiper arm is not properly contacting the base position of the wiper plate
       - either by wipe/swing angle, or  some loose play is allowing it to float above the wiper plate
       - and/or the flat brass stopper at the base of the trigger is not contacting with the screw that comes through the board  - (or that is extremely dirty)

There must be some experienced racers in your group who will be able to identify the issue with just a quick drive with the controller.

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Walks upright Unaided  *  Ties Own Shoelaces  *  Can Mispronounce Own Name In Five Languages  *  Mostly Aims Rattle Cans Away from Self
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On 8/31/2021 at 10:24 AM, SlotsNZ said:

Funny guy Sports Racer - - - planning to do all your driving with that above ? :lol:

I have lots of controllers including a few electronic ones but the Frankenstein is my favourite. 

It may look strange but I use it for all the tracks I race on and all the cars I have. 

 


May the downforce be with you.

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That's weird SportsRacer - your controller image has disappeared.

- So has r377. I spent some time writing a full and definitive reply regarding his issue, [Phil also took some time] and not a bean back since, in 2 1/2 months.

On 7/4/2021 at 10:55 PM, big den said:

Hi Shayne,

The difference is exactly where (or if) the red wire (brake) is installed within the track wiring. When you release the trigger (hopefully) you activate what is known as 'dynamic braking' in which a reverse current is applied to the motor thus slowing it down. If the brake wire isn't installed in the correct position there isn't any dynamic braking and the car will just coast rather than brake. (as was the case at my local track until February this year).

Den

Den, what you wrote there is not quite correct. 
Nothing is "applied" to the motor, the circuit simply becomes a dead short, and so the motor itself attempts to become a generator - into a dead short - thus causing the fixed magnets to resist the rotation of the armature caused by the rolling of the rear wheels moving back through the gear train, which is generating a conflicting magnetic field


Walks upright Unaided  *  Ties Own Shoelaces  *  Can Mispronounce Own Name In Five Languages  *  Mostly Aims Rattle Cans Away from Self
 My Track Oakland Raceway V2     Our Club  HMBRC     

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Hello Mark
I accept the science of what you wrote in the previous post.
However, the practical point I was wishing to make in my July 3rd  post was the importance of having the correct wiring in place to provide braking capability on a slot car track.
The desired effect is to slow down the motor, regardless of whether a force is being applied to the motor, or whether the motor is applying the force to itself i.e. by attempting 'to become a  generator'.
Interestingly 3 of the local tracks in Northern Tasmania are fitted with 'variable brake knobs' that allow people with basic hand controllers to have adjustable braking available to them. Some people actually prefer ZERO brakes!
Occasionally I get caught out by not returning the knob to the 'FULL ON' position when I am racing.
Den

 

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The part that I have a hard time getting my head around is that a brake pot is MORE brakes with LESS resistance. It's because you're resisting the power generation of the motor to act as a brake, so a higher resistance means less power is going back into the motor, and so it's braking less.

However it works, adjustable is always better than no choice, or only all/none as your choices. :)

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 Mr Flippant, you just did the same thing. Power is not “going back to the motor”.

for you, Den, anyone else reading this thread, it IS important to understand correctly how this works, or you will not understand how the addition of resistance to the circuit works,  thus reducing the motor generated braking, nor the impact of swapping out one motor for another with a stronger magnetic field/higher torque - and thus stronger braking.

Den - yes, I’ve come across tracks with a 25 or 50 ohm pot wired into the stations. But I didn’t know some Tassie tracks had that facility.
when I originally designed my controller stations, I put in a hole in the panels, for a pot to be mounted and offered that as an optional extra…but after a couple of years I only ever sold one set of stations with it…. Ah well. 
worse, we had a guy in club who sometimes wired his motors wrong way round, so would flip over the DPDT direction reversing switches - and not flip them back when he moved to the next lane :ph34r:

 


Walks upright Unaided  *  Ties Own Shoelaces  *  Can Mispronounce Own Name In Five Languages  *  Mostly Aims Rattle Cans Away from Self
 My Track Oakland Raceway V2     Our Club  HMBRC     

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Not being someone good with electronics, it can be hard to understand. I get that power isn't actually being generated and going back into the motor with an opposing polarity. I also get that the motor is a generator when power is not being supplied to it. I get that the resistance of the brake pot is what reduces braking effect as opposed to increasing it. What I don't know is the proper way to describe it such that a layman such as myself can understand it, while also NOT upsetting those who ARE good with electronics. ;-)

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