Maybe a 3, at most. It's not really hard, just a little time consuming. The worst part was merely getting parts I already had to work.

In it's simplest form, the second one I posted, it's holes for a hinge, a hole for the rod, and a couple holes for mounting. Adding the motor adds to the difficulty, but only slightly. I bought this motor off Amazon. (On mobile now, ugly links)

URBEST®DC 12V 50mA 5RPM 31Kg.cm High Torque Permanent Magnetic DC Gear Motor https://www.amazon.com/dp/B00NN3JHIM/ref=cm_sw_r_awd_tJ71ub08EXH2F

And i modified gears to work from an rc car. I could have bought gears, but didn't see the point.