[mwharton]

When running the configuration wizard,  engines 1,2 and 4 spin properly as expected.  However engine 3 oscillates back and forth.   Motor spins back and forth, less than a quarter inch.  Increase voltage just shakes it harder. 

[TheOtherCliff]

That happens when there are only 2 of 3 wires connected between ESC and motor.  That can be caused by burned ESC or motor.  Sometimes caused by bad solder joint, even a bad factory solder joint at bullet connector.

Did you ever see or smell smoke?  If so, it is burned for sure.

Don't raise the throttle to try harder when you see this because it can turn a loose connection on leg #3 into a burned out wire on leg #1 or #2.

Give a medium pull on each ESC to motor wire to see if one is not connected.

[mwharton]

Hello TheOtherCliff

Thanks for your help and validating my theories.  I finally got it working.   I replace motor, esc, flight controller, etc.

It turned out the alligator clips that I just bought was the problem.  As probably most people may do, they use alligator clips to determine which wires to attach for clock-wise or counter clock wise spins. 

Just another thing to keep in mind if this happens to you.

[mr_w]

There is actually easier way of figuring out how to connect motors, so they are always turning in correct direction.

If you take a closer look, three motor wires are always aligned in certain way, that is of course if all the motors you are going to use are same model. So lets just number those wires from left to right as 1 2 and 3. That is easy to figure out, place motor in front of you and count from left. Or right. doesn't matter.
Then look at your ESCs. If they are all the same, then they have same layout and lets name their outputs as A B and C.

So now you just need to make sure that adjacent motors are spinning in opposite directions. You do it like this.

Connect one motor to the esc like this: A1 B2 C3
Then next one to it, A1 B3 C2 (just two wires swapped!)
Then next one to it, A1 B2 C3 (this is same as first one)
Then next one to it, A1 B3 C2 (just two wires swapped).

The number of motors you use (maybe building hexa) does not matter, just follow the pattern:
- one motor directly (A1 B2 C3)
- next one just two wires swapped (A1 B3 C2)

And that's it. It might happen that *all* of them are spinning in wrong direction, but that is nothing bad. Just need to let LibrePilot aware of it, by checking the option "Reverse all motors" in Vehicle tab, and you are good to go.