# Braking Principle in Layman Terms



## Hornet (Dec 1, 2005)

I've been asked if i could explain the braking principle in a DC motor a little better.

I'm not gonna use North and South designations as it doesn't really apply for this simple explanation

Basically a slotcar has 2 motor mags that have a pulling and pushing side to the magnet,in correlation to the direction of flow of electricity through the arm.

When you apply power to move the car down the track,the flow of electricity is one way,when you apply a brake circuit or short circuit across the motors terminals,you basically turn the car into a generator,and it creates it's own internal electricity,"But" this flow of electricity is in reverse to the flow of electricity needed to make the car move forwards.
So now you've flipped the electrical flow path a 180,and what was positive is now negative,and what was negative is now positive.
What this basically does is make the poles reverse charged,and when you reverse the poles charge,the pulling and pushing side of an electrical field flipps.
But the car is still rolling forwards down the track,turning the arm,but it is now forcing the electrical field to run through the magnet field backwards to what it wants,because it's own internal electricity is flowing in reverse to what the car wants to continue forward.
So now as the poles of the arm enter the magnet field instead of being attracted to the magnet,they are repelled by the magnet,and as the poles leave the magnet field ,instead of the magnet pushing the pole away from itself,it is now trying to draw the pole backwards towards itself,applying a reverse torque to the arm.
The heat is generated because the magnet and electrical field create a pile of friction as they try to cross each other in reverse of what they want.
Hope that helps somewhat,it's a pretty simplistic description of the braking principle,but i hope it helps guys understand the principle a little better


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## alpink (Aug 22, 2010)

a DC motor, when not under power yet spinning, is a generator. to put a load (possibly a shunt) on that generated, albeit miniscule, source does have the effect of dynamic braking. the shunt(short) is across the leads of the motor (rail) and not the power source that makes the DC motor spin in it's normal application.


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## slotcarman12078 (Oct 3, 2008)

Exactly right Hornet!! This principal is used by among other things, diesel locomotives, which use dynamic braking to help slow trains down. Diesel locomotives use a diesel engine or two to generate electricity which powers motors to move the train. T jet types most likely will not benefit much from brakes as the back tires will more likely slide when the controller is let off than turn the motor (unless that chassis has a ton of coast like a nuther Dave chassis). Thanks for the plain and simple explanation!! :thumbsup:


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## Hornet (Dec 1, 2005)

It's a pretty simple explanation of the principle,.
Just hope it helps out the odd guy to have a better understanding of the braking principle,and it takes some of the confusion out of the principle:thumbsup:
A DC motor is a pretty simple thing,but some of it's principles can be hard to grasp.


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## slotking (May 27, 2008)

rick
let me help you

with a working brake system
when you let go of the controller trigger
the car stops faster than a car with no brake

hope that helps:wave::tongue::lol:



btw
pm me you address again!

thankls


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## Boosted-Z71 (Nov 26, 2007)

slotking said:


> rick
> let me help you
> 
> with a working brake system
> ...


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## Bill Hall (Jan 6, 2007)

*Jim Rockford...*

Along todays theme,

I'd like to add another "obvious-ism" as the effect relates to the slotcar universe. "Adjustable brakes" is what it's really about. Without a measure of control it's the scale equivalent of driving along and yanking the parking brake...then releasing it a mashing the throttle.


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## Hornet (Dec 1, 2005)

As long as it helps a few guys out,that's all that matters:thumbsup:

Mike i find a brick on the track is the best brake

Bill a truce,i enjoy your company too much to be at war:wave:

You too Al,i've enjoyed your posts lately,they're actually quite informantive:thumbsup:

Al i wasn't trying to step on your toes,so please don't think i was.
Rick


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## Bill Hall (Jan 6, 2007)

Sure Rick!

As for the topic. I'm never that far back on the heater to engage the granny circuit anyway. 

I'm just kicking back and waiting to see who sticks their head in this wicket and whether we can get some intelligent discourse on the effect.


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## Boosted-Z71 (Nov 26, 2007)

Bill Hall said:


> Along todays theme,
> 
> Without a measure of control it's the scale equivalent of driving along and yanking the parking brake...then releasing it a mashing the throttle.


Bill, I think that is how Drifting started, I watched some form of drifting competition on TV the other night & while I appreciate the car control I just cant imagine staying behind someone when you could clearly pass them.
Your explanation of the handbrake jogged my thoughts on drifting.

Boosted


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## slotking (May 27, 2008)

rick, I like the brick idea! LOL

I used to be a heavy break driver!
but when my brake pot blew, I have been racing controller brake free for years!
So I set my cars up for brakes

works well


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## Hornet (Dec 1, 2005)

LOL,me too:wave:

Basically what we're doing is maximizing the back EMF voltage while miniumizing the input voltage to the coils or poles.
Every DC motor creates back emf voltage as you turn it's coils or poles off,and it tries to back feed the built up voltage in the coil/pole back into the system.
When the coil/pole is "off" to input voltage,it's "on" to releasing built up coil voltage back into the electrical system backwards,that's basically what makes back emf.The coil/pole have an "on" and "off" side to the circuit,when "on" the pole is recieving input voltage
The electrical field is always flipping in a DC motor,depending on if your charging the coil ("on" ) or discharging it ("off")back into the system.
By shorting the terminals together the back emf voltage stacks up in the poles and creates a pretty big electrical field,that's where a pot or resistor in the brake wire circuit comes into play.
The pot absorbs some of the back emf voltage and turns it into heat, decreasing the back fed voltage from the pole,which also decreases the power to create the backwards electrical field,a smaller field translates to less pull and push on the pole by the magnet.
It's a little more complicated then that,but it's the basic principle of the dynamic brakes we're utilizing in our DC powered slotcars
Rick


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## AfxToo (Aug 29, 2003)

Rick, it's actually a lot simpler than you've stated. Making a slight correction to this statement from alpink:



> a DC motor, when not under power yet spinning, is a generator


to more correctly say:



> a DC motor, when spinning, is a generator


This is what makes shunt wound DC motors self regulating. Even under power the motor is generating a voltage that counters the applied voltage. This is why you can set a DC motor to a certain voltage and it stays at a certain RPM. Were it not for the generated voltage (back emf) the motor would spin out of control. This is also why the motor current drops significantly when the motor is spinning, because the generated voltage subtracts from the applied voltage. 

Dynamic braking simply puts a load across the motor when it is spinning and no voltage is being applied to the motor. All of the voltages, currents, and polarities that were in effect while the motor was under power are still the same, except the applied voltage is now zero and the motor is only acting as a generator. The heaviest load you can place on a generator is a short circuit, which is why a standard brake circuit with very low resistance results in the heaviest braking effect.


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## tossedman (Mar 19, 2006)

OK, that all makes sense Rick but what happens when you're in the southern hemisphere?

:wave:

Todd


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## Hornet (Dec 1, 2005)

Water flows counter clockwise in a flushing toilet,and up is down,lol:thumbsup:
Morning Todd


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