Ornithopter

The ornithopter has a mass of 3.89g and is constructed leveraging 3D printing techniques. The robot has an 85-second passively stable untethered hovering flight, showing the functional use of 3D-printed materials for flapping wing experimentation and ornithopter construction as well as for understanding the mechanical principles underlying insectflight and control.

Ornithopter Design 

The fuselage is designed to hold the motor, crank, and wing hinge.  The motor is placed as close as possible to the wing pivot point to center the mass. The wings are driven by a crankshaft connected  to the motors gearbox. The crankshaft includes two attachment points for the connecting rods powering the left and right wing to drive the wings in a symmetrical motion, These two attachment points are roughly 30 degrees out of phase from each other to compensate for the asymmetry of the crank position at any given point in the stroke.

The crank is designed to flap each of the four wings through roughly 80 degrees,  and when the flexibility of the wings is included, this angle is enough to allow the wings to clapand fling at the end of each stroke.

Two 10 mAh Lithium Polymer batteries are installed to power the motor and are attached on the opposite side to the motor to balance the mass.  

Wing construction

The 3D printed wings of the ornithopter are made of three functional elements: 

• the central beam
• the  surrounding frame
• the thin film wing surface.

The central beam is the most rigid portion of the wing and has the pivot point as well as the attachment holes forthe connecting rods. The outer frames of the wings are attached to the ends of the beam. The outer frames determine the flexibility of the wings and the deflection properties during flapping.  

The thin wing surface is a flexible film that extends through the area inside the outer frame. The surface has a thickness of 40μm, which is created by depositing two layers of material.   

Wing design

The wing has a length of 80 mm and a maximum chord of 30 mm.  The overall weight of the wing is approximately 0.3g and the thickness of the wing film 40μm.  The wing flaps at approximately 30 Hz through an angle of 110 degrees and produces a maximum lift force of 2.92g.  

The wing deflects to an angle of attack of roughly 45 degrees at the middle of the stroke. This angle of attack can be tuned by adjusting the flexibility of the main wing strut and the ribs that stiffen the interior of the wing.  

3D printing

3D printing expanded the possibilities for wing design, allowing shapes to replicate those of real insects or virtually any other shape. It has reduced the time of a wing design cycle to a matter of minutes. An Objet EDEN 260V printer and the Objet FullCure720 material were used to produce all printed components. This material costs roughly 0.22 USD per gram and the EDEN 260V prints with  a resolution of 42μm on the x-and y-axes and 16μm on the z-axis.