To achieve untethered flight, this latest iteration of the Robobee underwent several important changes, including the addition of a second pair of wings. The change from two to four wings, along with less visible changes to the actuator and transmission ratio, made the vehicle more efficient, gave it more lift, and allowed us to put everything we need on-board without using more power, the team said. The extra lift, with no additional power requirements, allowed the researchers to cut the power cord -- which has kept the Robobee tethered for nearly a decade -- and attach solar cells and an electronics panel to the vehicle. The solar cells, the smallest commercially available, weigh 10 milligrams each and get 0.76 milliwatts per milligram of power when the sun is at full intensity. The Robobee X-Wing needs the power of about three Earth suns to fly, making outdoor flight out of reach for now.