Brushless mCPX wobbles 90 seconds into flight

[supertoyz]

I've got a 100% microheli mCPX. The only things stock eflite is the servo's and 3 in 1 board. Throttle curve is 80% in ST1 and 100% in ST2 which I never use. I'm using the 550 mah packs. It flys pretty well for about 90 seconds then the tail begins to swing in circles like the heli is wobbling around it's axis. It starts out slow and builds into a significant wobble. If I switch it to normal mode (lower head speed) it goes away. I rolled the throttle curves back to 65% in ST1 and 80% in ST2 but haven't tried it yet. It seems like it's related to head speed but it starts out fine the develops as the voltage drops and I assume head speed along with it. Why then would switching to N and dropping the HS even further stop the wobble? Any idea's as to what's going on?

[mixfisto]

This is just a thought, but sometimes with higher head speeds My main gear slips a little, and makes the heli 'loose' and the tail will slowly and randomly lose direction...??
Maybe check to see if it's slipped or lost the flat spot on he shaft...

[everydayflyer]

ESC, version if flashed, motor ,gearing (pinion)?

Sounds like battery voltagre dropping or perhaps tail MOFETS getting warm and dropping in effeciency or perhaps the tail motor itself but most likely the LiPolys.

How old in time and flights are the LiPolys,do you store them at 3.8-3.85 or as flown or do you charge them right back upo and leave them so for days / weeks at a time
?

It seems that 98 % of LiPoly users have yet to learn proper LiPoly management.