  To date, insect scale robots capable of controlled flight have used flapping
wings for generating lift, but this requires a complex and failure-prone
mechanism. A simpler alternative is electrohydrodynamic (EHD) thrust, which
requires no moving mechanical parts. In EHD, corona discharge generates a flow
of ions in an electric field between two electrodes; the high-velocity ions
transfer their kinetic energy to neutral air molecules through collisions,
accelerating the gas and creating thrust. We introduce a fabrication process
for EHD thruster based on 355 nm laser micromachining and our approach allows
for greater flexibility in materials selection. Our four-thruster device
measures 1.8 x 2.5 cm and is composed of steel emitters and a lightweight
carbon fiber mesh. The current and thrust characteristics of each individual
thruster of the quad thruster is determined and agrees with Townsend relation.
The mass of the quad thruster is 37 mg and the measured thrust is greater than
its weight (362.6 uN). The robot is able to lift off at a voltage of 4.6 kV
with a thrust to weight ratio of 1.38.
