Motors / ESC not functioning properly

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I am just getting my APM2.5 board to work with my quadcopter. All has gone well 
until now. Firmware installed, hardware set-up, ESC's calibrated, etc. etc.

The first thing to mention is that I arm the APM with throttle at the lowest 
setting and the stick to the LEFT, rather than the right.Not quite sure if this 
is a clue. I arm the APM and increase the throttle and the motors all work fine 
as long as I keep it at relatively high speed. As soon as I drop the throttle 
to a LOW speed, strange things start to happen. The ESC and/or motors start to 
emit a sharp crackling sound.Some of the motors stop turning, the crackling 
sounds gets worse until such time the whole lot just locks up and the only way 
that I can recover is to power down and restart.

I have done the set-up of the board time and time again, re-flashed the EPROM, 
calibrated the ESC both individually and together, etc. etc. Still no luck. 
Please help.

Original issue reported on code.google.com by piyal.fe...@gmx.com on 8 Dec 2013 at 6:18

[GoogleCodeExporter]

I am trying to build a quadcopter but i am facing problem in calibration of 
ESC. I have 4in 1 EMAX ESC. I am using Arduino UNO to calibrate the ESC. My 
code is:

#include <Servo.h>

Servo esc;
int potpin = 0;// Pot pin
int val=0; 
void setup()
{
  esc.attach(9);// ESC attach to pin no 9
  }
void loop()
{
  val = analogRead(potpin);
  val = map(val, 0, 1023, 0, 179);
 esc.write(val);
  }
by using this code i have calibrated 2 ESCs (esc1 and esc2) out of 4 and they 
are working fine. but other 2 ESCs(esc 3 and esc4) are not calibrating properly 
although the ESC is giving the calibration confirmation tone but motors are not 
rotating.
my procedure is-
1- throttle the pot at full.
2- connect the li po and turn on the esc
3- after exact beep sending the minimum signal to ESC (by throttling pot to 
lowest position).
4- certain beeps come and finally calibration confirmation beep comes and ESC 
has calibrated. but motors are not rotating
Plz help me .

Original comment by amits0...@gmail.com on 27 Nov 2014 at 1:32