10 SERVO 12.2015
ROW, ROW, ROW YOUR ROW-BOT
Robots are pretty good at some things. However,
none of those things are energetic autonomy: the ability to
operate continuously and indefinitely without dependence
on humans for refueling. There certainly are robots that
operate autonomously for long durations; they’re either
feeding off of radioactivity, or they’re relying on solar
panels that don’t work half the time. A better option (at
least in some situations) might be robots that forage for
food like animals do, taking care of their own energy
needs all by themselves.
This is only a slightly crazy idea. Fuel cells that are full
of living microbes are a real thing. At the Bristol Robotics
Laboratory in the United Kingdom, they’ve been
developing a robot called Row-bot that can swim around,
harvesting energy directly from the water using a
microbial fuel cell as an artificial stomach.
According to the researchers, Microbial Fuel Cells
(MFCs) generate electricity by “electrons mobilized by the
redox reaction that takes place in electrogenic bacterial
anabolism.” More specifically — in the case of their device
— they explain that “raw organic biomass is used as both
an inoculant for the bacterial culture and the anolyte that
In other simpler words, microbes eat stuff in the
water and poop out electrons, and as long as you’ve got
enough water with stuff in it to keep the microbes fat
and happy, they’ll keep giving you electrons that you can
use to make your robot do things.
MFCs work in all kinds of water, including fresh
water in rivers and lakes, seawater, and even waste water,
and they actually clean the water as they go which is nice.
Microbes are kind of tiny and each one doesn’t
produce a lot of energy, so to do anything useful you
either need a whole bunch of them (multiple fuel cells) or
a very efficient robot. Row-bot is very efficient, modeled
after a water beetle. It has two side paddles to move, little
floaty feeties to keep it from drowning, and a
microbial fuel cell in its tummy.
It has a mouth, too, that it can open to ingest
water for the fuel cell, and also a fuel outflow port on
its posterior end. Each time the robot opens its
mouth, it swims forward, ingests fresh water into its
MFC tummy, digests for three minutes, and then
expels the water out the back as it swims forward
again, making room for a fresh gulp.
Row-bot stores the energy generated by the
As long as Row-bot has water to swim through, the
MFC makes it more or less energetically autonomous,
although the current design is mostly a testbed for
integration of the MFC with actuators to see how well it
works. There’s a lot more optimization that needs to
happen like reducing body drag and finding the most
efficient combination of materials to use for the paddles,
as well as altering the “stride” of the robot to better
mimic actual water beetles. Also, multiple MFCs could be
configured in series if you need more power for those
aforementioned laser turrets.
Eventually, the researchers suggest that Row-bot could
be developed for applications such as remote sensing and
environmental monitoring and clean-up, although space
exploration isn’t out of the question either.
Row-bot with mouth open (inset shows mouth closed).
Image: University of Bristol.