RC-Monster Forums - General ESC Theory Discussion

RC-Monster Forums (https://www.rc-monster.com/forum/index.php)

- Brushless (https://www.rc-monster.com/forum/forumdisplay.php?f=12)

- - General ESC Theory Discussion (https://www.rc-monster.com/forum/showthread.php?t=8279)

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

Quote:

Originally Posted by zeropointbug (Post 173806)

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.

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?

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

Quote:

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.

Quote:

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.

Sorry it seem that i can't edit my previous post anymore

http://pix.nofrag.com/8/1/0/bf124943...35eb817185.jpg

Mister-T,

Good info. Do you follow the BLDC thread in rcgroups? Some of the guys there have said that the Atmel MCUs do a better job in brushless application. That's why a lot of companies use the ATMEGA8 and ATMEGA16. Most of my controllers that have those will drive all motors that I have very smooth. They might not have all the memory like the Silicon Labs one, but some manufacturer can stuff a lot of info in them.

I have seen some interesting stuff with STm microcontroller, they do have there own patented way to detect back EFM, so it can pretty much always start the motor even under load (compressor application they said)

Quote:

Originally Posted by Mister-T (Post 173937)

I think some of my Kontroniks have a STM MCU, it's not really clear. Maybe tht's why they have such an incredible start up. I haven't been able to get any of my Jazz controllers to cog on start up.

I wonder what CC used on the MMM?

Quote:

Originally Posted by zeropointbug (Post 173957)

I wonder what CC used on the MMM?

Rubycon (http://www.newark.com/39K2343/passiv...-35ZLH390M8X20). The picture in the link is only for your reference.

http://www.rc-monster.com/forum/showthread.php?t=11912

Quote:

Originally Posted by lutach (Post 173962)

Rubycon (http://www.newark.com/39K2343/passiv...-35ZLH390M8X20). The picture in the link is only for your reference.

http://www.rc-monster.com/forum/showthread.php?t=11912

I think he was asking about the microcontroler, not the capacitor ;)

Quote:

Originally Posted by Mister-T (Post 173966)

I think he was asking about the microcontroler, not the capacitor ;)

I must've been day dreaming about caps :rofl:. Castle uses Silicon Labs MCU.

Quote:

Originally Posted by Five-oh-joe (Post 173801)

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...

Couldn't you just send a small pulse to two or three coils to sense position when stopped? I noticed that the quark ESC would always make an outrunner hum a bit when idle. It also started up outrunner like a champ with no audible noise.