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Old 02-07-2006, 09:56 AM   #1
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Arrow diode

can anyone please tell me what a (schottky)? diode on a motor does exactly? and what are the benefits of running one verses not? and what about that capacitor on esc's- sorry for my ignorance but i am a converted 1/8th scale buggy racer.
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Old 02-07-2006, 10:10 AM   #2
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Diodes help protect your ESC from reverse voltage coming back from the motor, that's why you can only use them with forward-only ESCs. Capacitors are like batteries, they store electrical energy and can be charged/discharged in a matter of seconds. When you go full throttle, there is a spike in voltage, a capacitor helps smooth this spike so that your servo doesn't lose voltage.

One-ways let the front wheels spin independently from one another, so when you turn the outside wheel can free roll faster than the inside one (which is getting power). Running a one-way is faster in the right situations, but only if you can drive it.
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Old 02-07-2006, 01:17 PM   #3
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to expand on the diode part-

A motor acts as a generator when the shaft is spun by an external force. This spinning causes back emf (Definition- Back Emf is an Electromotive force that occurs in Electric motors where there is relative motion between the armature of the motor and the external magnetic field. When the coils of the motor rotate, the magnetic flux threading through the area between the coils is constantly changing. This causes a back Emf that, by Lenz's law, opposes the motion of rotation.) The purpose of the diode is to use up all the voltage emitted from the motor while braking(when the car is spinning the shaft of the motor). Many components are prone to fry when a voltage is applied in reverse of what it is designed, specifically the f.e.t.s located in the esc.
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Old 02-07-2006, 08:18 PM   #4
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Quote:
Originally Posted by rcguy2477
to expand on the diode part-

A motor acts as a generator when the shaft is spun by an external force. This spinning causes back emf (Definition- Back Emf is an Electromotive force that occurs in Electric motors where there is relative motion between the armature of the motor and the external magnetic field. When the coils of the motor rotate, the magnetic flux threading through the area between the coils is constantly changing. This causes a back Emf that, by Lenz's law, opposes the motion of rotation.) The purpose of the diode is to use up all the voltage emitted from the motor while braking(when the car is spinning the shaft of the motor). Many components are prone to fry when a voltage is applied in reverse of what it is designed, specifically the f.e.t.s located in the esc.
Wau...!! You've given me a Brain lock after reading those...!!
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Old 02-07-2006, 11:29 PM   #5
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On low turn motors I was told to use higher diode values, right now i have a total of 35amps. is this enough? Will this protect my speedo 100%?
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Old 02-08-2006, 08:52 AM   #6
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The most common way to address this issue is to use two normal diodes that are included with motors/esc's in parallel.
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Old 02-27-2006, 10:06 AM   #7
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does it do any good when used with stock motors? i read somewhere that it inreases RPM - I could use that
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Old 02-27-2006, 10:10 AM   #8
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I asked the same question on from my local club guys. One of the club guru's (MattS) answered with this article from Novak

From teamnovak.com

The following is a brief explanation of Schottky diodes and their use with electronic speed controls.

A Schottky diode is a special type of diode with a very low forward-voltage drop. When current flows through a diode, it has some internal resistance to that current flow, which causes a small voltage drop across the diode terminals. A normal diode has between 0.7-1.7 volt drops, while a Schottky diode voltage drop is between approximately 0.15-0.45 this lower voltage drop translates into higher system efficiency.

At partial throttle, a speed control switches the battery power to full-on and full-off at varying duty cycles. The ratio of the duty cycle determines the throttle setting for example: 50% on to 50% off is 1/2 throttle. The Schottky diode is used to carrying the re-circulating current from the motor during the 'off-time' while the speed control is at partial throttle.

Similarly, the motor in a car is like a big inductor. During the off-time at partial throttle, the motor will not allow the current to just stop. Instead, the voltage across the motor will reverse, and current will flow through the Schottky diode. If no diode is present, the current will flow through a parasitic diode built into the brake transistors. The current flows through the Schottky diode before it will flow through the brake transistor because the forward voltage drop of a Schottky diode is less than the brake transistor diode (this is why Schottky diodes are used and not other types of power diodes).

For the highest efficiency, during the off-time while the motor continues to flow current, the voltage should ideally be as close to zero as possible. One reason Novak uses an external Schottky diode is because the closer the diode is to the motor, the lower the voltage drop during this period. This is due to the voltage drop through the wires back to the speed control. This will also reduce some radio noise due to the current spike not having to travel a long distance.

Speed controls like the Hammer, Racer, Tempest, Atom and the Cyclone are racing speed controls. For the ultimate performance, an external Schottky diode is used (The Cyclone has one built-in also.). As a result, the speed control is smaller. Also, as a convenience to the newcomer, Novak's sport models have it built-in.

Another reason Novak uses an external Schottky diode is to prevent the brake transistors from overheating and losing brake power. When a Schottky diode is built into an ESC, it is positioned next to the brake transistor. As the Schottky heats up, it heats the brake transistor and consequently loses braking power (the on-resistance increases).

The hotter the motor that is used (i.e. the lower the number of turns), the higher the current that flows through the Schottky diode. In some cases, two diodes connected parallel must be used (connect both striped ends to motor positive and both non-striped ends to motor negative).


Hope this helps, it helped me.

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Old 02-27-2006, 07:21 PM   #9
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My GTX speedo has an internal shotke diode, am I correct?

I also use an external diode at the motor. am I helping, hurting or just adding weight?
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Old 02-27-2006, 07:44 PM   #10
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Default diode number

can you tell the international number diode IN.... for i use in lrp SR?
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Old 02-27-2006, 10:40 PM   #11
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What is consider the correct a diode? On the motor or the esc? Thanks.
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