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Old 07-20-2006, 04:32 PM   #1276
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Interesting things, these electric motors...
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Old 07-20-2006, 04:38 PM   #1277
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The power capacitor is there to supress ripple current caused by the transistors switching on and off.

This ripple current, if left unchecked, causes extra heating in the transistors and thus, less efficiency.
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Old 07-20-2006, 04:58 PM   #1278
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Could you explain ripple current a little better? What exactly is it? I assume it's power fluctuating up and down, or bouncing back and forth between the batteries and the esc? If so, how exactly does it start rippling? Does the power sort of bounce back from the esc to the batteries when throttle is cut?

Sorry for all the questions but searching did me no good whatsoever. I even found a 10 page tutorial on every kind, or what appeared to me as every kind, of capacitor in the world, and the only mention of ripple was that capacitors work as ripple filters, but it didn't explain anything on that subject.
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Old 07-20-2006, 07:23 PM   #1279
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The cap acts like a valve and only allow`s the voltage to flow one direction and never be able to go backwards, causing interferance or heat or, I guess, "ripple`s" ....
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Old 07-20-2006, 07:35 PM   #1280
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wow I had no idea tht it didn't allow voltage to go backwards. Good to know.
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Old 07-21-2006, 12:17 AM   #1281
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Quote:
Originally Posted by Wild Cherry
The cap acts like a valve and only allow`s the voltage to flow one direction and never be able to go backwards, causing interferance or heat or, I guess, "ripple`s" ....
I thought thats what a diode did????
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Old 07-21-2006, 02:25 AM   #1282
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Idd thats a diode explained there, thats blocks current going one way and allows current to flow another way.

Ripple voltage is a small alternating voltage that is on top of your constant DC voltage.

To get it out you mostly need a capacitor (or thats what I remember, definately in a powersupply a filter needs to be calculated on maximum current draw and allowed ripple voltage (filter can be just a capacitor or a capacitor and a coil or...).

Thats all I can say, its too long ago for me...
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Old 07-21-2006, 06:15 AM   #1283
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The cap smooths voltage ripples.

How?

WHen you get hard on the throttle, you are pulling big amps from the battery through the ESC.

As a result, the battery voltage drops. Some enterprising person can look up a battery discharge chart to confirm this. But the quicker you suck the juice out of a batt, the lower lower voltage it will be at. There's only so much energy in a battery - somehting has to give. This is a function of ohms law.

Anyhoo, this is highly inefficient for the ESC which then heats up. I'm not sufficiently educated electronically to explain why ESC's don't like the voltage drop, but this is my understanding of it. But i believe resistance increases as the voltage drops.

With a cap however, the drop in voltage causes the cap to discharge. Caps discharge in the region of milliseconds (in rc apps), and this bumps that drop back up.

The ESC thus sees a average very small drop in voltage and is more efficient. No heating. ALthough caps are polarised, i'm not sure they act as a voltage gate.

The bigger the cap, the more it is able to fill the drop in voltage. Of course, the actualy voltage rating of the cap is important too. Caps with lower voltage charge quicker and react faster to the drop.


The voltage gate thing is the function of a DIODE, not a cap.
THat's why schottky diodes are used on brushed ESC. These diodes stop the large backwards current from flowing into an ESC when the brakes are engaged.

WHen the brakes are engaged, the spinning rotor acts like a generator, sending a big voltage spike into an esc. An external schottky is more robust to these loads. Most esc's have built in diodes, but at racing speeds this taxes the esc's tiny integrated electronics.

That's why an external schottky is used...
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Old 07-21-2006, 03:31 PM   #1284
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Interesting Interesting...

Anyone know why brushless motors don't act as a generator when coasting?
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Old 07-21-2006, 05:12 PM   #1285
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That's a good question HVAC... I think it may have to do with the fact that a brushed motor has a D/C connection. Just positive and negative. However, the alternator on your car is basically a driven brushless motor. But the stator (can) has to be powered to create the magnetic field in order for it to generate power.. I may be totally off on this one, just a guess.

I can't wait to see the 3.5r in action... That's going to be some ridiculous friggin power...
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Old 07-21-2006, 06:30 PM   #1286
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Well, the current in a motor/generator is made when you pass a magnet through some wire.

Okay that's a bit simple. IF you wind some wire into a tube and pass the magnet through that, then you have a small electrical current. In a brushed motor the same relative movement happens but the magnets are fixed.

So a BL motor is really just generating a current too..But instead of a + and a -, there's er.. three+ and three - right? Seeing as there's three phases inside.

Oh.. and from what i understand, the "Brakes" on a brushed motor are the result of an electrical short placed across the terminals. Not sure how a BL does it..
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Old 07-21-2006, 07:17 PM   #1287
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Probably the same way just alternated like the throttle.
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Old 07-23-2006, 01:56 PM   #1288
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1. What oil should I use to lube my 4300 bearings (there are two . . right?)

2. How many races/days/hours of use should there be between relubes?

3. What procedure is used to ensure the correct amount makes it into the bearing and doesn't just attarct more dirt?
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Old 07-26-2006, 07:48 AM   #1289
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Is Trinity coming out with a brushless system?
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Old 07-26-2006, 02:15 PM   #1290
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They already make a brushless motor that is compatible with the Mamba 25 and Tekin Rage escs, but I doubt they will come out with their own esc. I don't think Trinity has ever made electronics.

http://teamtrinity.com/shop/motors/cobalt_b.html
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