Homebrew ESC questions

[fregon45]

Hi all, I'm trying to design and build a high quality ESC based on a PIC (628 or similar). I plan to use variants of it in cars (w/ brake), boats (water cooled) and airplanes (LV cutoff). I've looked at a lot of the homebrew designs out there and most of them consist of a PIC directly driving one or two MOSFETS with a few other features like BEC, LV cutoff, and brake.

Usually the homebrew circuits are very simple. When I look at a professionally built ESC, though they seem to be pretty complex. What is there to a good comercial ESC that the homebrew stuff doesn't have? Do commercial designs use fancy signal conditioning or other glitch-reducing features not found in homebrew stuff? I want my design to be as good or better than what I can buy.

Do commercial designs use FET drivers? If so, what is the advantage over driving the MOSFETS directly from the PIC? I plan to drive up to 5 or 6 MOSFETS. BTW, weight and size aren't too much of a concern for me at this point (within reason). Thanks for your input.

Nathan

[zagisrule!]

Older ESC's (commercial and home-brew) often relied on comparators and a slew of passive components to generate PWM in proportion to input signal.

Modern MCU's (PIC and AVR) have greatly reduced size and complexity.

Industry standard as far as one-directional brushed componentry goes - 2 resistors and a cap for LVC, 2 resistors and a NPN BJT for driving the P-channel brake MOSFET, gate and grounding resistors for the main switching N-channels. An LED, resistor and possibly a switching BJT. Also a diode and cap for the motor usually.

Reversible controls have double the MOSFET's and driver circuitry to comprise the H-bridge.

Commercial ESC's are usually only better in the fact that their software might be better developed, but this is not something a hobbiest can't do! :)

Signal conditioning, glitch-reduction and all the other features are software based, including beeping and the like as well as programability.


-Matt

[zagisrule!]

Most commercial designs use MOSFET drivers when using all N-channel on BL designs (gate must be driven above rail to switch the positive rail with N-chan).

You could probably get by without it but watch gate capacitance. Because MOSFET's are voltage-controlled you won't be sucking much current from the PIC pin but the inherent gate capacitance may cause issues unless you have a beefier drive setup for the multiple MOSFET's.



-Matt

[Comatose]

Mosfet drivers are really used more often in industrial drives where the drive voltage is a couple hundred volts. An all-N bridge or three phase bridge drive is pretty easy to do with discretes at the voltages we run.

Zagisrule pretty well summed up a typical commercial brushed ESC. what do you have thats more complex than that?

Glitch reduction is easy to add to software, its really just bounds checking and holding the last good signal for a period of time, then shutting down if another good pulse doesn't come along in a predefined period of time. A moving average filter on the input will make it appear smoother and less glitch prone as well.