thread title tells all. the unit landed hard at an angle and got sand in two of the motors. blew out and WD-40 but still wouldn't work. dug through my stuff and found a set of four replacement motors. plug-in units so no soldering! managed to disassemble and remove old units. put replacements in one at a time so as not to confuse the wiring. problemo; the new units had red/blue and red/black wires; the old ones had red/yellow and red/green! (the little black/white red/blue on top were the same to indicate clock/counter). turns out the receiver/board has two sets of sockets, one of six and one of four. the six-socket is for lights and sequence doesn't matter. the four then are for the motors. tried to launch, no luck. wrong colors. re-did. the red/black were the motor wires and the red/blue for the lights. (I'm very glad I got the motor assemblies, not individual motors and stems, which would have been a bear to put together). unit tried to fly but rotated and stumbled. more problemo. figured might be prop issue but props matched rotation. researched and found that the motor plugs had to be in sequence. got it but still no good. found a way to reset gyro. no fix. concluded unit had suffered a fatal software error and reluctantly ordered a new one (original was $100, now down to $51, made the decision easier). got and opened up the new one. as I kinda figured, the motors alternated between counter and clockwise (right front counter; right rear clock; left rear counter; left front clock). this contradicted the engrish directions in the UDI user guide. so I switched the two rear motors, ensuring motor wires plugged in proper sequence. WORKS!!! HA HA HA HA HA!!! 1) VERY happy I bought this with the plug-ins. no way I could have done all that soldering. 2) frowny face for UDI for poorly written directions. had to find a privately-done tutorial on internets to get as much done as I did. without the new one to compare I might have never gotten a fix. 3) sucks to spend money on a new unit, but at least it's half. (still in the box and could return but won't); I want to modify the frame (those rings round the prop blades) to try to get it less wind-driven (any little breeze pushes it). doesn't fly as well as the Syma but much better camera. I might remove one of the camera units and try to plug in the Stryker (Syma, Stryker, same thing).