Possibly the most compact, simple, cheapest and fastest iron farm.

Setup:
1. Waterlog the Mechanical Drill and the Andesite Funnel.
2. Apply rotational force to any point in the machine (64 RPM seems to be the sweetspot).
3. Watch the fan. If it sucks, reverse the source of the rotation. If you are unable to do so, change the 2 Cogwheels behind the fans to Encased Chain Drives or a Belt.
4. Setup either a disposal system or a storage for the flint. You can dig a 1x1 hole below the Smart Chute to let them despawn, or place fire/lava.