MartinL:
The 50Hz generated by the servo library too slow and in any case is software based so is prone to jitter.
You can easily increase this by modifying this line
#define REFRESH_INTERVAL 20000 // minumim time to refresh servos in microseconds
in Servo.h
e.g. reduce to 10000 which equates to 100Hz.
How much you can increase this is limited by the need to fit 4 2000us pulses (plus some overhead) in this window.
Obviously if you have some conflict between servo and another library then this may make that worse. But on its own I found that making this change gave a significant improvement in terms of getting a quick and smooth response from a quadcopter.
adelphysi:
i have already tried the pins you mentioned ( it is known that they are PMW out put on uno)
however it is not necessary to use them , i have tried that( as Joop Brooking says ^_^)
How was it? Better/worse/no difference? What made you choose to use the 'servo' approach instead?