I bought an inexpensive, radio-controlled helicopter for my 13-year-old son this past Christmas. Traditionally, “Santa” would get him one of the $15 two-channel types, but this year, I more than doubled the budget and bought a three-channel device -- lift, pitch, and yaw.
After he opened the gift, I watched him launch it on its maiden flight. It was immediately apparent that something was wrong. He seemed to be able to control only two of the channels -- lift and pitch, but the helicopter acted as if the yaw control was pegged full on. There was a “trim” control that allowed him to zero out the yaw, but he could then only turn the helicopter in one direction. With disappointment in his voice he said, “Something’s wrong Dad, can you fix it?”
Being a mechanical engineer, my normal approach in these situations is to disassemble whatever needs fixing, and hope that the failure reveals itself. It was clear that the helicopter was operating properly, so I took the controller apart and examined its circuit board. I looked for obvious failures -- burned out components or broken wires -- without success.
I had resigned myself to ordering a replacement controller when I noticed that the potentiometer attached to the yaw control was soldered to the circuit board differently than the pitch and lift potentiometers. It appeared that two of the three connections of the yaw device had been soldered together to the circuit board common ground. I broke out my soldering iron and corrected the problem.
The board seemed to be manufactured using automated wave soldering equipment, so I believe all the controllers must have the same problem. It appears the monkeys were out to lunch during any design verification phase granting approval of the controller assembly process.
This entry was submitted by Eric Hamkins and edited by Jennifer Campbell.
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