12V to a lego 9 v motor

Hi, i built a lego robot that has 2 x 9V motors. \one for each wheel.

I am using a 12V 1.25A adapter (adapter of an HP scanner)to power the motors
and a parallel port optocoupler circuit.

Will i damage the motors if i use 12 Vs? Tey seem to work fine at the
moment.

And one of my motors is slightly slower. Is this normal or should i look for
new motors.It goes 15 cm to the right every meter or so.


Thanks
Teoman
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Did you check the web site first?: http://www.crynwr.com/lego-robotics