General ESC Theory Discussion

[BrianG]

Originally Posted by GriffinRU

No, No, No...

Only capacitors, and just a good bank of ultarcaps will convert low current LiPo into short-term (need to define voltage drop and timeframe, formulas available) high current killer power pack.

Inductor can be in motor leads, but not in power. Ripple current covered by capacitors, voltage drop can be covered by ultracaps and zeners (in one half).

Yeah, kinda figured, but doesn't hurt to ask...

[MetalMan]

Why not just capacitors? I'll admit I haven't yet studied inductors much, but capacitors still seem more logical to me. As you stated an inductor in series with the positive rail between the battery and ESC will require some hefty wiring, and that alone would cost more than I'd care to spend (due to wrapping of the thick or high-strand count wires over the core). In another post somewhere you mentioned that it's difficult to get extra capacitors close enough to where they need to be on the MMM, but what about modifying the case to allow additional wires/capacitors, sized/spec'd appropriately to handle excessive ripple current?

[BrianG]

Yes, caps can help, but a good combo of both may be better. I don't want to figure out the math of it right now until someone a little more knowledgeable on the topic can chime in. I'm sure it's been thought of at some point, just thinking out loud really.

[Serum]

what exactly IS the problem? is it the internal resistance of the batteries that gets worse on a high load?

An inductor would be adding too much resistance.

What is the exact problem? if lipo's are not up the task, perhaps the voltage ripple kills the esc; in that case it might be an idea of adding these diodes that short above a certain voltage. put these between the 3 motorwires and it would prevent an overvoltage to occur.

[zeropointbug]

Is it Zener Diodes you are thinking of Serum?

About the inductor, it's kinda hard to say what that would do on an ESC; but wouldn't a large cap bank like the one I have make more sense? Looking at my eagletree results from last year when I have my monster quark running, and comparing that to the replacement quark, I have discovered that the voltage drop at a given current level is definitely less. This could possibly be an error in the eagletree, but I don't really know. Just my two cents.

Anybody have a link to some Low-ESR caps that are similar to what is on the Mamba Max ESC? I was thinking about adding a cap bank to help it run a little cooler (only gets to around 120F with a fan and a medusa 4800 kv pulling some hefty gearing). I would like it to run even better though... It's starting to get into the low 90's down here in Florida, so I'd like some extra cooling insurance.

Also, I should solder them closest to the power leads, yes?

[lutach]

You can look around www.newark.com, www.mouser.com and www.digi-key.com.

Edit: I got some Axial type capacitors that I'll be adding them up. They are the same width as most of the ESC I have and I'll probably hook it up to my Scorpion controller. They are Nichicon 50V 1000uF each. Should make a good bang when connecting .

[GriffinRU]

Originally Posted by Five-oh-joe

Anybody have a link to some Low-ESR caps that are similar to what is on the Mamba Max ESC? I was thinking about adding a cap bank to help it run a little cooler (only gets to around 120F with a fan and a medusa 4800 kv pulling some hefty gearing). I would like it to run even better though... It's starting to get into the low 90's down here in Florida, so I'd like some extra cooling insurance.

Also, I should solder them closest to the power leads, yes?

Have you checked the links under my signature?

The best caps for our ESC's in current form factor would be Panasonic FM-type. Check datasheet for lead spacing and dimensions, look for lowest ESR and voltage at least 25% higher than you battery Voltage.

I like Atmel's and there is nothing special about finding rotor position without spinning, but tricky :) Solutions available but not every programmer now how to do math (or willing to do math...) on micro without floating point support...

Thanks lutach. Could I just pluck some off of a PCB I have laying around (say...from a computer's mobo?).

[lutach]

Originally Posted by Five-oh-joe

Thanks lutach. Could I just pluck some off of a PCB I have laying around (say...from a computer's mobo?).

I don't the the leads will be long enough, plus you won't know how many hours they've been working.

[zeropointbug]

Unfortunately caps from mobo's are lower voltage (~5v on mobo's)... and lot's of the time they are only lower rated 85C rated, which usually means not so low-esr.

Go on ebay and type in Nichicon low-esr 35v caps, and choose between 250uF and 500uF, they are usually the most effective for space/performance wise.

Lutach, a button size ultra-cap will have a relatively high esr, even compared to a lipo pack. You might want to look for something larger... I have found the Maxwell's to be the all around best for this.


http://www.maxwell.com/ultracapacito...l/bcap0120.asp These are the Maxwell ultra caps that I would use... 120F, 2.5V each (You will want +20% pack voltage handling), and are ~$15 each.

[lutach]

Originally Posted by zeropointbug

Lutach, a button size ultra-cap will have a relatively high esr, even compared to a lipo pack. You might want to look for something larger... I have found the Maxwell's to be the all around best for this.


http://www.maxwell.com/ultracapacito...l/bcap0120.asp These are the Maxwell ultra caps that I would use... 120F, 2.5V each (You will want +20% pack voltage handling), and are ~$15 each.

Yes, Artur said the same thing, but I see that some companies are using Capxx capacitors and they have higher esr then the ones I looked at. I can get the ultra caps fairly cheap, but I want to see what these other high capacity caps can do and they are much cheaper and comes in higher voltage.

Edit: I have also spoken with a company that makes a hybrid, low esr, high voltage and high capacity cap, but the price on those are up there.

Thanks guys for the info. I'll have a look around on the 'net.

Ok, I did some rummaging, and found my fried HV maxx controller, so I just stole the cap off of there. It's a 2700uf 25v low ESR (105 C) cap, so I'm guessing that should definitely be a good little cap to install on the mamba max, no? My only issue....I need a hotter iron. The traces on the PCB, the heatsink, and the wire leads themselves suck up WAY too much heat to get anything done. So either I need to use the 100 watt weller soldering gun my dad has, or connect the cap on the actual battery leads.

Any suggestions?

[Mister-T]

Hello,

Just to add my stone to this thread, most microchip/onboard controler manufacturer provide some thick documentation about there chips.

The most used in inexpensive BL ESC is the infamous Atmel Mega8, Acccording Mr del castillo (need quote) they didn't use it because they need more processing power to drive some motors and add more features.

http://www.atmel.com/dyn/resources/p...ts/doc8012.pdf

AVR444: Sensorless control of 3-phase
brushless DC motors
Features
• Robust sensorless commutation control.
• External speed reference.
• Overcurrent detection/protection.
• Basic speed controller included.
• Full source code in C.
• Source code can be adapted to a new motor by changing parameters.
• Several I/O pins/peripherals not used for motor control. Can be used for other
purposes, such as status LEDs, communication or user input.
• Works without modification on the pin and source code compatible devices
ATmega48, ATmega88 and ATmega168.

bla bla

The magnitude of the back-EMF is directly proportional to the motor speed. This
makes it extremely difficult to detect zero-crossings at low speed, since the signal to
noise ratio is very small. The sensorless commutation scheme presented in this
application note will thus not work during startup and at very low speeds. A number of
strategies for sensorless startup of brushless DC motors have been proposed over
4 AVR444
8012A-AVR-10/05
the years. These differ in complexity and computational complexity, and there does
not seem to be one solution that fits all. Furthermore, many of these startup methods
are patented.

BEMF vs. Hall Sensors
An important physical difference concerning determination of the rotor position via BEMF or
using Hall sensors is that for the BEMF the change of the magnetic flux in time within the coil
gives the BEMF where for the Hall sensor the magnetic flux is sensed. Because of this, for sensorless
commutation based on the measurement of the BEMF the rotor has to move before one
can determine its position. In contrast to that, Hall sensors always give a valid signal representing
a position. The position of the rotor is represented by a three bit vector with a resolution of
60° within the electrical period. For most BLDC motors, the Hall sensors are mounted within the
120° scheme that is direct compatible to the BEMF. Nevertheless, there are BLDC motors with
Hall sensors mounted within a 60° scheme resulting in a different Hall signal pattern. Those 60°
Hall sensor BLDC motors are not taken into account here.