Are DUPLO gears compatible with LEGO gears? Can I make a transmission from DUPLO gear (Early Simple Machines Set 9656) to regular-sized gear?
To the best of my knowledge, the gears are not compatible in any way. The teeth on the DUPLO gears appear to be far too large.

One option could be to use one of the included DUPLO pulleys and create a connection to the Technic system that way: