My parts from Digikey arrived yesterday (after only 2 days) so last night I spent an hour soldering up everything into the receiver unit and it works great! Of the 5 FETs I bought, I tried out the IRL3713 FET first and didn’t have any problems fitting it in (other than my usual sucky soldering skills) and from some initial tests it appears to work just the same as the stock FET, but with 260A current carrying capacity, 330W power dissipation, and an on-resistance of only 0.0033 ohms. I had to cut the plastic case on the receiver unit to fit the heat sink, and I had to remove the connector for the drop module but hadn’t intended on ever using it anyway. The FET may have been fine without the heatsink, but the heatsink definitely won’t hurt, it was just harder to install and now it doesn’t look stock anymore. (As it turns out after subsequent runs, the heatsink is definitely NOT required, even when running a 3S lipo pack, so for simplicity sake, I would avoid using the heatsink. I’ve since removed mine and it works fine, barely warm to the touch). I used a dab of Arctic Silver 5 heatsink compound to ensure good thermal conductivity to the heatsink. Computer builder geeks love this stuff because it has an incredibly low thermal resistance, probably the lowest available in the industry for PC use, but who says it you can only use it on a CPU? I had some left over from the last couple of PC’s I built so I thought, why not? The stuff works great, but is a mess to clean up.
I still had some radio glitching, even after adding (3) .1uF caps to the motor. So I decided to add (3) .1uF caps straight to the PCB in about the same fashion as you do on the motor. I also changed out the tiny stock diode for a beefier 600V 1N4005 diode which should work a bit better at suppressing any voltage spikes caused by the motor. Now there’s just a small amount of rudder and elevator glitching and only at really low throttle, so it should be fine. A Futaba 6CH radio is sounding really good to me about now, and Tower has $25 off any order over $149. I need to pick up a better radio, soon.
I haven’t gotten to fly the Cub with the newly modified speed controller yet since the weather here has been super windy and cold this past week and today it’s raining. But I have just run the motor full blast for several minutes and the heatsink just barely gets warm, so I think this mod should last through just about any sized brushed motor I can throw at it.
The stock receiver module, IRL3713 FET, 1N4005 Diodes and some solder
Diode and FET installed, the gray band on the diode connects to the (+) red side
0.1uF caps installed across the motor and diode
Top view housing cutaway with new FET
Adding the Arctic Silver 5 heatsink compound
A thin layer is all that’s necessary, this is probably too much
The finished product but with way more current capability than before
Installed in the Super Cub
