slipstick:
A 7805 might just do for a single SG90. It's definitely not enough for 3 or 4 of them.But first, what type of "9V battery" are you using? A lot of the servos problems we see round here are people trying to use those little rectangular 9V PP3-type batteries. They will not deliver anywhere near enough current to drive even a single servo. And since you mention a motor shield I guess you have some motors too? No chance without a decent battery/power supply.
Since you're the only one who knows exactly what you're trying to do perhaps you should provide the schematic. And if you are going to use 7805 you're going to need some capacitors too.
Steve
Thanks for the reply Steve,
I'm using a 'rectangular' duracell 9V battery which seems to drive one servo fine, but as soon as I wire it up to more than one, I start getting some problems.
Yes, it is for a little autonomous robot so there are motors as well as a couple sensors as well.
Could you suggest a more appropriate battery solution?
Regards
Kaleb