AVR-Chat

A while ago I put together an 8 channel fan controller, for controlling
the speed (via PWM) of computer fans.

Works fine with fans, but last night I attached a couple of little DC
motors to it (for a little robot project I am working on with my son)
and to my surprise the AVR started resetting.

It would give a short burst, then reset (motor would run for a little
bit - maybe a quarter of a second).

Does anyone have any idea what could be causing it? As I said it works
fine with the fans. Output is via logic level MOSFET's.

Many thanks
Dean Claxton