I've developed a circuit for my model aircraft, which requires 3.3V @ 100mA. My aircraft uses a 3S LiPoly, which ranges from 9V - 12.6V. When the motor is off, the 3.3V supply is good; very low ripple. However, when it spins up, the battery voltage ripples, and the supply voltage to my MCU occasionally dips below ~2.5V, and this occasionally resets it, and at the very least it causes problems with the rest of the analog circuitry.
I've attached a diagram of my system.
What can I do to reduce this problem?