A group of researchers based at Canada’s University of Windsor have made use of 3D printing technology to investigate an unusual phenomenon in the natural world. They 3D printed replica ''robo-toads'', similar to other 3D printed robotic versions of animals that have been used for research in the past. These robo-toads were used to track the mating behaviour of toads. The males of a species of toad that lives in the forests of Central America turn yellow for one day a year, during their mating season, and behavioural ecologists Daniel Mennill and Stéphanie Doucet wanted to find out why.
The project started when the scientists observed the behaviour in Costa Rica. They were there to study birds, but were surprised by a remarkable transformation in the toads they saw. On the first day of heavy rainfall after a long period of dry weather, toads emerged that were bright yellow in colour, like a lemon. When they returned the next day, they had turned back to brown again.
The team wanted to find out why this happened, theorizing that it was a way for the male toads to impress potential mates. They wanted to produce replica versions of the toads that could be placed amongst the real ones to stimulate particular types of behaviour through their colours. Starting out with molding plasticine and clay toads, they figured out that the yellow colour was a way of toads signaling which sex they were. They then wanted to know how females made their choice among similarly-colored males, and this study required a higher level of realism in their models.
The idea to use 3D printed robotics came from Lincoln Savi, a University of Windsor Masters of Science graduate student. The advantages of 3D printing would be that the replica toads could be printed to a high enough level of accuracy that real toads would be fooled, and they could also incorporate robotic mechanisms that enabled them to move around, stimulating real toads through movement as well as colour and shape.
Savi started out by making use of photogrammetry, a technique that takes multiple photos of an object and uses software to creates a digital 3D model from the 2D images. This took a while, however, as the object he was taking photos of was constantly hopping around and would rarely strike a pose long enough to be captured.
"I only got 11 photos before he moved’’, said Savi. ‘’I couldn't get any photos of his underside and he was in some leaves, so there was some geometry hidden by leaves."
Making do with the best images he could get, Savi 3D printed the model and then sculpted the parts that he was unable to properly capture in the digital version. The initial printing took just one hour, and he was at work on the sculpting for around seven hours. He then applied different coats of paint to get the colours right, one for yellow toads and one for regular brown ones. All that was left was a robotic mechanism to enable the replica toad to move around in a vaguely realistic way.
(all images, credit: CBC.ca)
"The robo part was actually pretty easy," said Savi. "I used some programmable microprocessors and some servos and just made a simple program that chooses a random angle and makes the toad move there."
A research team is now in Costa Rica with the robo-toads, waiting for the heavy rainfall to start. They will expose females to their 3D printed creations and hopefully get a little closer to solving the mystery of the yellow toads and their mating rituals.
Posted in 3D Printing Application