It's always difficult to make these types of comparisions because there are endless permutations and combinations of motors, props, spinners, motor mounts, etc, but if I am being asked to generalize, then I would say that the weight difference between a system consisting of a Contra Drive and a Neu Motor with Budd Mounts, and your Hacker C50 system with an APC 21x14 prop, a Tru-Turn Spinner, and also with Budd Mounts, is about 57 grams.

However, if you substitute the Neu motor with a Hacker C50 motor the difference will be more because the Neu without a gearbox is lighter than a Hacker without a gearbox. Also, if you don't use Budd Mounts for your single prop system the difference is more still, etc...

Ignoring comparisions, the all up weight of a Contra Drive system with a Neu f3a Motor, our latest 22x20 props, (at 65 grams each ..) and Budd Mounts, is about 810g +/- 5g. The tolerance is needed because there is variation from prop to prop.

Generally, if you have enough weight margin for an outrunner, then you have enough weight margin for a Contra Drive.

Brenner ...