One of my esc's must be bad because 3 motors spin up and number 4 just spurts around a little. This is a 4-in-one esc. I'm thinking I can just add in another single esc to replace the bad one. Power it and set the signal wire to the flight controller. I would be interested in your thoughts.

All ESC have the same settings? Did you verify that?

If there is space in your build to do that, then there's no reason why this wouldn't work.

If you haven't tried swapping the motor with one that does work properly, just to check that it's not an issue with the motor or your soldering, it would be a good idea to do that first.

I am going to piggyback on Mephi's post and ask some easy questions on this in case there are others who read this thread later trying to research the same question. 

Shouldn't the new ESC match certain things with the rest of the build such as:

• The new ESC can handle the protocol of the others (This one is kind of an obvious requirement)
  
• Match or exceed amperage
  
• I would think that making sure other things are similar such as if the 4-in-1 is running BLHeli_S then the new one should to
  
• Maybe try to find the literal equivalent in single ESC to the 4-in-1? Like this: This 4-in-1 = this one
  

Well, intentionelly i was asking about the settings on the 4in1. On some i received the settings were different on at least one partial ESC.
So it is a good thing to check and match the settings/FW Version even on factory new 4in1´s.

The esc in question is the Cicada 4-in-1 10 amp. The motor in question is the DYS BE 1104 7500kV.

I soldered pig tail wires from suspected bad esc number 4 to motor number 3 and also good esc number 3 to motor number 4. Opened motors in Betaflight for testing.

Turns out, it was motor number 4 and not a bad number 4 esc. Cigar goes to UNSEEN and much appreciation to all.

If this did turn out to be a bad esc partial, It does seem that a matching single esc , same brand, amps and features would have worked.

Interestingly, one of ESCs in my Cicada 10A 4in1 also died on the bench, but I have replaced the blown FET and now it's ok :-)

my concern would be to truly disabling the bad ESC. I would not want this one to catch fire in mid flight just because it was still sucking some energy but not directing it to a motor...I mean is it possible to fully disable just one ESC in a 4-in1 setup?

(06-Jun-2017, 08:23 PM)Kleinerbug_FPV Wrote: my concern would be to truly disabling the bad ESC. I would not want this one to catch fire in mid flight just because it was still sucking some energy but not directing it to a motor...I mean is it possible to fully disable just one ESC in a 4-in1 setup?

If there is nowhere to send the power, it's not using any. The laws of physics apply to ESCs just as they apply to anything else!

(07-Jun-2017, 09:46 AM)unseen Wrote: If there is nowhere to send the power, it's not using any. The laws of physics apply to ESCs just as they apply to anything else!

  my tought was that it would still recive a Signal...but you can just not hook this one ESC to the FC. I think you are right. But still I would not risk iit and just change the entire thing.