'Flipperbot' to provide turtle solution to sandcrawling

Presented today in Bioinspiration and Biomimetics, Flipperbot has been designed to test how real-life organisms, such as seals, sea turtles and mudskippers use flippers and fins to move on surfaces such as sand.

The 19cm-long robot was built by Nicole Mazouchova, working in Professor Daniel Goldman’s Complex Rheology and Biomechanics (CRAB) Lab at the Georgia Institute of Technology, and Dr Paul Umbanhowar from Northwestern University.

It weighs 790g and crawls using two flipper-like front limbs, spanning 40cm. Each limb is driven by small servo motors and has a thin, lightweight flipper at its end. During the study the robot was tested on a 122cm-long bed of poppy seeds and was recorded using a high-speed digital camera.

The researchers believe that the improved understanding of flipper-based locomotion gained from their study could inspire the design of future multi-terrain robots that can swim and walk effectively using the same appendages.

Prof Daniel Goldman and his group have previously studied the high walking performance of hatchling sea turtles, and the goal of this new study was to use a robot to further understand the mechanics of flipper-based movement on land.

In a statement Prof Goldman said, ‘Flipperbot allowed us to explore aspects of the sea turtle’s gait and structure that were challenging, if not impossible, to investigate in field experiments using actual animals.

‘One of the main findings of our paper was that when the robot was fitted with a free wrist, it was able to move more effectively over the ground as it allowed the flipper to remain locked in place within a solid region of sand and thus disturbed less material during the forward thrust.

‘With a fixed wrist, the robot also interacts with the ground that has already been disturbed by its previous steps, which hinders its movement.’

As well as the wrist flexibility, the researchers also investigated the different depths to which the flipper penetrated the poppy seeds, while also measuring the body lift, flipper thrust, the drag of the robot’s base and the amount of ground that was disturbed.

Co-author of the study Dr Paul Umbanhowar said, ‘Our modelling shows that flipper driven locomotion on soft ground is largely determined by simple granular physics.

‘But the inherent sensitivity of this type of movement to disturbed ground means that very small changes in gait or body structure can cause dramatic decreases in speed.’