I see you are building an Antweight robot. I get that you are using gutted servos, but perhaps you'll get to the point where you will want to use low voltage motors and microcontroller powered by a small LiPo. Here is my solution for that:
I am using a mega8 (just because I had some laying around and wanted to use them, you can use 168) with a 3.3V regulator from a 3.7V LiPo. To drive tiny pager motors I still need an H-bridge, so only a low voltage one will work. After much research, I got a $2 FAN8200 from here
. This chip needs one or two pins from the micro per motor. The least you can use is 3 pins total, or, if you tie both enable pins high, you can use only the 2 direction pins to drive the motors. here is a quote from the site:
To implement sign-magnitude PWM, the Enable pin is pulsed and IN1 determines direction. For locked anti-phase, IN1 is pulsed and Enable is used to enable/disable the motor. We have used PWM frequencies up to 20kHz.
Microbot is a small line follower that uses the FAN8200 to control a pair of Solarbotics gear pager motors powered by a single Li-Poly battery. Microbot weighs a mere 1 ounce!
Using this chip allowed me to use the remaining free pins from the microcontroller to light up a 7 segment digit like Axon II has for a nice light show and marquee text.
Good luck on your project!