My 450 is behaving a  bit erratically. Have just put in new servos and a swash. It flies fine for some time (3-4 btys) and then suddenly makes a dip towards the right. Has done this twice now and both times managed to save the heli.
1. The servos do not bind. Have checked them all.
2. The FBL system is working fine. Will hover almost hands free.
When its going down it seems that the rotor is losing power, but it's as if the the pitch on one blade suddenly changes.
Has anyone experienced this?
Could it be because of heat? ESC ?
I am quite at my wits end here..
Any and every help/ suggestion is welcome..
Thanks

The issue seems to be with electronics as it's behaving after 3- 4 batteries means after good 20 -25 minutes of flight time when the electronics is hot, majorly the issue can be because of loss of power from the ESC, also try replacing the servo positions and see if it starts to dip the other way, this would give you a fair idea of servo issue.

BTW what all electronics are you using on this 450?

Hellyflyer

Do you let it cool down between flights ?

I am using the standard Walkera electronics which came with this heli.
@ Anwar - Yes, I think heating is the issue here, but I don't fly 3-4 batteries at one time. Just 2. It's most prob the ESC losing its head with the heat. Going to now try only one battery at a time and see what happens. Will keep you all posted.
Appreciate the quick replies. This is a nice forum.

Turn the main rotor by hand. resistance can come from one way bearing or a rear rotor belt twisted at the factory among other things. When you turn the rotor as fast as possible with your finger and let go the main rotor should continue to spin for a while, at least a few rotations. Any resistance in the drive train can cause ESC to overheat and the heli will loose control. Also check for vibration during take off; unbalanced blades from the factory was my second heli's problem causing the gyro to build up on correction data and the heli would loose control. If you take off the tail piece to inspect the belt be sure the rear rotor turns counter clockwise as the main rotor turns clockwise after re-assembly, otherwise the heli will lose control.
 I have two V450's in fuselages.
Here is a video of one of my V450's in an Airwolf scale fuselage.


Here is the other V450D01 in a Swedish Army fuselage carying an iPhone 4 around:


Point is the stock V450 can carry a workload without overheating. Other factors in your problem can be one or more servo link rods need adjustment or a bad servo and yes I know you said your servos do not bind but I've had a tail servo that did not bind and my heli behaved just like yours till I replaced it. Even two turns on a main rotor rod link can cause balance problems in my experience.

Thanks everyone for your replies and suggestions. I stripped the head and re-lubricated everything. Seems to have solved the problem and it flies fine now. Seems the one way bearing was sticky..