The SC6 Electronic Speed Control
by Bruce K. Stenulson, SKYFOX RESEARCH & CONSULTING
P.O. Box 69, Fairplay, CO 80440
Designed and flown since early 2001; Revised / Updated 02/12/2003
Suitable for 5 cell to ~12 cell flight systems (while using BEC), and for up to 14 cells without the BEC. Conservatively designed to operate to ~30 Amps without heat sinking & much more (60+ Amps) if additional heat sinking is added to the latest generation HEXFET power transistors.
1.1 x 1.7" PC Board; <½ ounce assembled, without wires. Completely assembled with 16 gauge wiring, arming switch, & Rx connector, weight of one of mine is about 7/8 ounce.
This ESC uses conventional through-hole component mounting techniques, and the latest generation HEXFETS for minimal heat generation during operation. This PC board assembly project is hobbyist-friendly. (Unlike Surface Mount component designs with their extremely small contacts & impossibly close spacing, you can actually work on this PC board if you do manage to somehow kill it! :>)
This is a Proportional, Very High Rate PWM (Pulse Width Modulated) RC Aircraft speed control: The pulse repetition frequency was selected through oscilloscope analysis in typical motor drive dynamic testing. As a result, the SC6 has better efficiency in mid-range throttle settings, and cleaner motor drive waveforms.
On board BEC: Features 5V 1.5 Amp Low Dropout L4940V5 voltage regulator in a TO-220 case for good heat dissipation characteristics; needs only 5.5 volt input to supply 5.0 volt to RC system; (or the SC6 can optionally be built without the BEC feature, for use with a separate Rx battery pack.)
This SC6 can be built with either one or two IRL1404L ‘Logic Level Gate' High Efficiency HEXFETS: these new MOSFETS have .004 Ohm on resistance ("RDS on") with 5 volt gate drive per device, and only .002 ohm On resistance when two HEXFETS are used. When installed in the cooling air flow inside your aircraft, additional heat sinking should not be needed. Optionally, for more modest current draws such as typical speed 400 systems, only one of these MOSFETS would be needed.
You can also build it with a pair of smaller case, lighter weight I-PAC MOSFETS, such as the IRLU3103, which are rated at .019 ohms ON resistance each, giving .0095 ohms for a pair- very usable for 20 Amp continuous current applications.
TECH NOTES: No ‘Low Voltage Cutout' is used in this ESC : (I was personally tired of two other commercial ESC's that would cut out before motor RPM had dropped off very noticeably. When flying an aircraft with this ESC, I'll listen to the motor in the air, and cut the throttle for a landing when the RPM is dropping off, indicating I'm close to the end of the pack's capacity. There should be some battery reserve for more power application if needed in setting up for a landing approach. Since modern radio receivers are capable of running on lower supply voltages, this should not be a problem if you don't try to ‘fly the battery dead'. If you are inexperienced in electric flight, it might be safer to use an ESC with a built-in Low Voltage cutoff. I've now completed the SC7, which has this feature as well as a prop brake, which is especially useful to stop folding props from wind-milling so they'll fold quickly. )
On 5 cell systems, using the BEC option on the SC6B might be a questionable approach- you'll have to avoid crowding the battery capacity when flying; but on the 7 to 10 cell systems I had in mind when designing this SC6, there should be a reasonable safety margin for chopping the power yourself when you notice the power / RPM dropping off during flight, and landing with plenty of reserve power to keep the radio system happy. You could otherwise use a small Rx battery supply, and not use the BEC section- the choice is yours.
On battery system cell counts above 12 cells, it might also be better to use a separate receiver battery.
Above is the component placement diagram, as well as the parts designations which corespond to the SC6 circuit diagram above. 5 pages of assembly, testing, and installation instructions, and a parts list are included with each PC board ordered. DIGIKEY is my preferred source for these special MOSFETS; all of the other electronic components are also available from them.
Yes, I have built several of these for my own use over the last three years, and fly them regularly in several aircraft; they do work well. No, unfortunately I don't have time to offer full parts kits, and I do not offer completed ESCs at this time, and my consulting business keeps me busy so that I don't have time to answer a lot of questions- sorry!
(Etched & drilled Bare PC Board available for the SC6 for $12.00 including full instructions, plus delivery.)
Bruce K. Stenulson
P.O. Box 69
Fairplay, CO 80440