When mechanical engineering graduate student Faye Yap saw a dead spider lying in the hallway, it got her thinking about whether it could be used as a robotics component.
Turning dead spiders into mechanical grippers may be some people’s idea of a nightmare scenario, but it could have tangible benefits. Spider legs can grasp large, delicate and irregularly shaped objects firmly and gently without breaking them.
So, in collaboration with mechanical engineer Daniel Preston, Yap and his colleagues at Rice University discovered a way to make the legs of a dead wolf spider unfurl and stick to objects .
This new type of robotics was called “necrobotics”.
Interestingly, spider legs don’t have muscles for extension, but instead move their legs using hydraulic pressure: they have what’s called a prosoma chamber, or cephalothorax, which contracts, sending internal body fluid into the legs , making them spread.
So the team inserted a needle into the spider’s prosoma chamber and created a seal around the tip of the needle with a glob of superglue. Pressing a small puff of air through the syringe was enough to activate the spider’s legs, achieving a full range of motion in less than a second.
“We took the spider, we put the needle in it not knowing what would happen,” Yap says in a video on the Rice University website.
“We had an estimate of where we wanted to put the needle. And when we did, it worked, the first time, right away. I don’t even know how to describe it, that moment.”
The team was able to get the dead spider to cling to a small ball and used this experiment to determine a maximum grip strength of 0.35 thousand newtons.
They then demonstrated the use of a dead spider to pick up delicate objects and electronics, including having this necrobotic gripper remove a jumper wire attached to an electrical board and then move a block of polyurethane foam.
They also showed that the spider could support the weight of another spider of roughly the same size.
(Preston Innovation Laboratory/Rice University)
Because spiders extend their legs by exerting hydraulic pressure from the cephalothorax, when they die the hydraulic system no longer functions. The spider’s leg flexor muscles go into rigor mortis, but because the muscles only work in one direction, the spider curls up.
While most artificial robotics components are fairly complex to manufacture, spiders already are, and (unfortunately for arachnophobes) are in plentiful supply.
“The necrobotics concept proposed in this work takes advantage of unique designs created by nature that can be complicated or even impossible to replicate artificially,” the researchers say in their paper.
Spiders are also biodegradable, so using them as robot parts would reduce the amount of waste in robotics.
“One of the applications we could see it being used for is micromanipulation, and that could include things like microelectronic devices,” Preston says in the video.
One drawback of the dead spider clamp is that it begins to experience some wear after two days or after 1,000 opening and closing cycles.
“We believe this is related to joint dehydration issues. We believe we can overcome this by applying polymer coatings,” explains Preston.
The researchers experimented by coating wolf spiders with beeswax and found that their mass decrease was 17 times less than the uncoated spider over 10 days, which meant that they retained more water and that their hydraulic system could run longer
This study was published in Advanced Science.