This layering is important for two
reasons. First, there needs to be
precise control and actuation,
together with an easy user interface
that can start, stop, and add songs.
Second, it is important to be able to
extend the band to an arbitrary
number of instruments.
TeamDARE built the circuit boards
for this and etched some themselves.
With respect to mechanics, each
new robot in the band has seen a
steady increase in complexity. The
guitar is the most simple of the three.
It consists of six plectra on little arms
that each actuate one string. The
arms are rotated with a servomotor.
The left hand of the robotic guitar
player consists of a grid of pneumatic
pistons that press the string down at
the correct fret position. The robot
controls the volume of each note by
using a second servomotor to control
the height of the plectrum with
respect to its string.
The drums conceptually seem
simple: one stick for each tom,
controlled by a servomotor. However,
in order to get the timing, volume,
and bounce of the drum sticks right,
the system necessitated a very
complex motion controller.
Furthermore, the pedal for the hi-hat
and the muting of the crash cymbal
were implemented using pneumatics.
The pan flute robot is the most
complex of the three in terms of
mechanics. Instead of having a nozzle
for each tube, the team wanted to
use a single pipe and rotate the pan
flute back and forth. In order to get
the correct tone out of each tube, the
nozzle needed to be controlled over
three degrees of freedom:
horizontally, vertically, and on one axis
The airflow influences the pitch of
the sound. On each tube of the pan
flute, a semitone can be produced in
addition to a note. For this, a tube
needs to be partially obstructed. The
team implemented this using a small
rubber cushion that mimics lips and a
second airflow supply.
The whole band currently runs
on eight microcontrollers and two
PCs, due to the layered design. Most
of the code on the microcontrollers is
written in C, with the exception of
some small critical parts that are
implemented in Assembly language.
The PC software is mostly written in
C++. For some nice 3D visualization
on a big screen, the team wrote a
player in C++ and GPU code which
runs on a second PC.
In addition, a lot of software has
been written to automate the team’s
song writing, mostly in C and C++.
Basically, these tools convert MIDIs to
a format suitable for the robots; they
can also simulate how a song will
sound when played by the bot band.
TeamDARE already has plans in
case they win the $10,000. It would
be to finish a fourth band member
which would be a double bass that is
already in progress. SV
Boca Bearing contest page
Links to contestants and videos of
their projects in action
Boca Bearing site
Video of TeamDARE
robot band performing
SERVO 06.2012 13