A robot crab called Wavy Dave has been having a rough time as his real life rivals ripped his claw off.

The robotic crab was created by researchers at the University of Exeter who wanted to see how fiddler crabs react to rivals. Male fiddler crabs have one oversized claw, and they attract females by standing outside their burrow and waving it.

Researchers wanted to investigate how rival crabs affect each other's behavior, so they created a robot crab – nicknamed Wavy Dave – to venture out onto the mudflat where a large number of male fiddler crabs were displaying.

Dr Joe Wilde created Wavy Dave using a 3D printer and electronics that are controlled using an app via Bluetooth. The 3D printing was based on publicly available 3D scans of fiddler crabs.

He found a 3D printer to make a model, and taught himself enough robotics to make a crab that waved its claw. He then developed an app to control the crab via Bluetooth signals.

Like real fiddler crabs, Wavy Dave has one claw larger than the other. The printed major claw was glued to a mobile joint that allowed vertical movement. This joint was then fixed to a plastic base and a length of metal wire passed through the plastic base, allowing the printed claw to be joined to a Tower Pro Micro Servo SG90. This micro servo was attached to an Arduino Uno Rev3 microcontroller that controlled the timing of the micro servo movement and therefore the vertical movement of the printed claw, emulating the waving of a male fiddler crab.

The Arduino microcontroller was also connected to an HC−05 Bluetooth serial transceiver, allowing the wave speed of the robot to be changed remotely via Bluetooth connection to a phone. The robotic stimulus male could wave at two speeds: a ‘slow’ speed of one wave every 2 s, simulating low-intensity waving; and a ‘fast’ speed of one wave every 1 s, simulating high-intensity waving.

Thousands of crabs live on the mudflats where the study was conducted. The researchers set up the robot crab 30cm from a real male’s burrow, with two cameras recording.

Wavy Dave then waved his robotic claw and the researchers watched how the rival crabs reacted. 

The results show that males were less likely to compete when Wavy Dave's claw was bigger than theirs, possibly because they expected to lose or were fearful of being attacked.

Some crabs took issue with the robotic intruder, though. According to Dr Wilde:

“The females realised he was a bit odd, and some of the males tried to fight him."

“One male broke Wavy Dave by pulling off his claw. We had to abandon that trial and reboot the robot.”

You can see Wavy Dave getting attacked in the video above.

The conclusion reached by the study was that male crabs do indeed respond to competition with Dr Wilde stating:

“Our findings reveal the subtle ways in which these crabs adjust their behaviour to compete in a dynamic environment, investing more in signalling when it is likely to be most profitable.”

More Information

Robot crab reveals how males compete in claw-waving contest

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