SERVO 05.2014 27
If you're a tree, there is a significantly increased
likelihood that this pruning robot will climb up you
and violently lop off as many of your limbs as it
The reason why a pruning robot is actually a
really good and important idea is that climbing trees
and then holding on with one hand (or no hands)
while sawing big heavy bits of them off is incredibly
dangerous, with injury rates about 10 times that of
working in a factory.
This teleoperated robot means that you can
stand very far away while the pruning gets done. The
'bot seems to do a good job — able to climb up and
down trees with no trouble while cutting branches
off in a spiral motion.
At 13 kilograms, the robot can drive straight up
trees between 6 and 25 centimeters ( 2. 3-9. 8 in) in
diameter at 0.25 m/s, while tackling branches with a
diameter of less than 5 cm. It can automatically adapt
to a variety of tree morphologies (whatever that is), and is relatively energy efficient since it
can support itself passively on the tree by using its own weight to securely grip the trunk.
Most of the testing of this robot has so far been in an "experimental forest," where the
trees seem to be about as straight and perfect as a sprouting telephone pole. Continuing
research will involve making the robot a bit more robust towards different sorts of trees and
foliage, and teaching it the difference between trees that it should try to prune and tall
humans that it shouldn't.
ETH Zurich has taken its quadcopter fail recovery
software they've been working on — that can completely
shrug off the loss of an entire propeller — and pulled it out
of a controlled environment to show that it works in the
The algorithm is executed on the quadcopter's
onboard microcontroller, and the only sensors required
are the quadcopter's angular rate gyroscopes.
They use blinking LEDs mounted on the quadcopter's
arms to indicate a virtual yaw angle, so that the pilot can
control the vehicle with the same remote control
commands after a failure. As an alternative to the LED
system, an onboard magnetometer could be used to
track the vehicle's yaw angle. Alternatively, using more
sophisticated algorithms, the system could be made to work
using only the rate gyroscopes.
The failsafe controller uses only hardware that is
readily available on a standard quadcopter, and could thus
be implemented as an algorithmic-only upgrade to existing
systems. Until now, the only way a multicopter could
survive the loss of a propeller or motor is by having
redundancy (e.g. hexacopters, octocopters).
However, this redundancy comes at the cost of
additional structural weight, reducing the vehicle's useful
payload. Using this more efficient technology, quadcopters
can be utilized in safety critical applications because they
still have the ability to gracefully recover from a
This fail recovery process is completely transparent to
the user flying the quadcopter; you don't even have to flick
a switch, and the vehicle responds to all of the same control
inputs. You're probably not going to manage quite as soft of
a landing as you would otherwise, but the point is that the
quadcopter doesn't just immediately reduce itself to rubble.
It can be steered, hover, then land.