mike_flight Heliman Location: Troy, NY - USA
| Thanks MMcGinnis for such a great tutorial on how to fix the CX 4-in-1 controller!
Last week I bought a CX and burned out my controller just by tipping the helicopter over onto the floor (it didn't even break anything). After reverse engineering the motor drive circuit, it was pretty clear to me that the output stage is woefully under-rated, not to mention there is absolutely no current-limitting circuitry whatsoever. IMHO, E-Flite either forgot to add a couple of 10-cent parts, or they wanted to generate an additional $50 - $100 of revenue immediately after each CX sale (I would like to think they were just a little forgetful).
Anyway, I came across a newer part made by International Rectifier that comes in the same package as the IRF7313, but which features about half the ON-RESISTANCE. The part number is IRF7907PbF which can also be purchased at www.digikey.com ($1.12 in quatities of ten. With the IRF7907PbF at 25C ambient temperature, both outputs can drive over 9 amps continuous current. I also ordered some 7A pico fuses (part number F2318-ND) to install in series with the motor. That should be large enough to sustain aggressive flying, yet it oughta blow if the rotor comes to a screaching halt with the brushes straddling across two windings).
I'll try to follow up when I receive the parts and test everything out. |