>I have used a "trim" series resistor at times
>(very low ohms) to make two motors run at the same
>speed, assuming relatively constant load. The
>other solution of course is to go to proper
>encoders with closed loop speed control.

No, the other solution is to connect the motors together in parallel using
a relay or by putting the resistor in series with the supply of the two
H-bridges. Or by using crappy batteries which will be like the resistor,
only better ;-).

In general, if the motor voltages are never low (>>1.2V) then the H bridge
reverse diodes will couple the motors together fairly well if they run out
of sync. MOSFET (again! ;-) H-bridges will couple them even if they run on
lower voltage.

Peter

PS: To all diy homemade dc-motor driven robot users: You really should use
a small resistor in series with your batteries, going to the motors. The
starting current is several times the run current...

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