This paper presents the design of a highly manoeuvrable and untethered under-actuated legged piezoelectric miniature robot called PISCES. It comprises of a piezoelectric patch bonded onto a thin diamond-shaped aluminium plate to form a planar unimorph piezoelectric actuator, with three rigidly attached legs to generate locomotion. Unlike other under-actuated robots found in literature which uses compliant mechanisms, our robot utilizes three different standing wave vibration modes of a thin diamond-shaped aluminium plate and well positioned rigid leg positions to achieve forward, clockwise rotation and anticlockwise rotation motion using a single piezoelectric patch. This approach have the benefit of generating a more predefined motion and thus more controllable.
A finite element analysis approach is proposed to understand the modal vibration of the 2D unimorph actuator and how the geometric placement of the rigid legs together with the robot center of mass can be utilized to achieve under-actuated planar locomotion is described in detail. To verify the proposed locomotion, PISCES of a size of 90 × 60 × 11 mm, weight of 21 g is built. It is able to achieve a linear speed of 203.5 mm/s for forward motion, an angular speeds of 7.7 Revolution Per Minute (RPM) for clockwise rotation and an angular speed of 10.6 RPM for anticlockwise rotation using an input sinusoidal voltage of 100 V amplitude. Under a payload of 100 g, it moves with a linear speed of 110.8 mm/s and angular speeds of 4.1 RPM clockwise and 12.5 RPM anticlockwise. A tether-less remotely driven PISCES featuring a full suite of onboard electronics, and a more detailed experimental verification, analysis and characterization of PISCES are also demonstrated in this paper.