DaVinci Drives has really made a name for itself a few years ago by developing high performance electric bikes that used the high-end Astro Flight RC motors. The distinctive feature of his drives were the chunks of billet aluminum that were cut into beautiful and well-designed brackets, which mounted these motors to various bicycle frames.
The company had calculated out a lot of variables and optional configurations during the first year he was developing hot rod RC drives for E-bikes. The high-end Astro motors they used has the ability to run at very high RPMs, and to access the extra power that is waiting there, you have to use quite a bit of reduction to get the RPMs back down at the wheel speed.
Something that DaVinci did on a monster yellow trike was to use a smaller 20-inch driven wheel, which simplified several aspects of the design process, concerning the amount of reduction needed. Since they like to stick with things that have proven to work well for DaVinci, the following bikes also use a 20-inch driven wheel.