I have two 12V motors (300 RPM) running from a L293D H-bridge circuit. I find that the speed when I provide 12V is not satisfactory. Will it damage the 12V motors if I provide 18V or 24V? Will they go at higher RPM at higher voltage? The L293D circuit has maximum rating of 36V anyway.
The datasheet for your selected H-Bridge indicates a maximum amperage of 600mA per channel. It seems like this should be enough for your 12v motor. (whats the model number of the motor?)
So this could mean that your power supply is the problem. You are thinking about raising voltage:
But unless I misunderstand, what you need to do is this:
Unless of course one of your motors draws more than 600mA then you need a different H-Bridge