Thanks guys, I figured it was something around that area causing the issue, I'll have a rethink about this area.
The 4 servos I have connected will all move if I don't use a 6v regulator, but they can't move much when there's a load on them.
My understanding is the higher the load, the more current a servo needs to move. If there's only 2 connected, then they can move with a load with no problem. I'm guessing this is to do with the amount of current it can draw from the 4 AA batteries?
Can anyone reccomend what I should use as a power source if I want to have 6 servos that will have a load on them (google suggests you should budget 1 amp per servo but that sounds pretty high to me)?
Ideally I would like it to be standard type batteries (AA, AAA, 9v batteries etc...) or is a wallwart the only way to produce the ampage needed for this?
Cheers