electronics in the sport. The brain is a
Nios soft processor, running inside a
Cyclone FPGA, made by Altera. The
processor runs a Web server that is
hooked back through an 802.11
wireless link with user commands
coming from a USB joystick hooked
to a laptop. The laptop runs a
custom application which allows a
copilot to tweak various parameters
during combat.
The toughest challenge the team
hit with Cyclone Drive was maintaining directional information inside the
machine. In order for the robot to
process a command to go “North,” it
needs to know where North is, in the
driver’s reference frame. Quadrature
encoders are used on the wheels,
and this is pretty reliable for relative
direction. However, the wheels slip,
change diameter based on speed,
and when the bots go flying on
impact, all bets are off! Thus,
some system is needed for absolute
correction of heading, locking
the robot’s reference frame to the
driver’s reference frame.
Their first approach was to use a
two axis magnetometer to measure
the Earth’s magnetic field. Measuring
that magnetic field in an environment
with 18 HP of brushed DC motors
that see peak currents over 1,000A
was extremely difficult and required
extensive lab testing. They had
to test a variety of different
shielding, grounding, physical
locations, wiring architectures, and
algorithm parameters for the
magnetometer to best insulate it
from the motor, motor controller, and
power line noise.
They found that on the second
version of the bot (with its lower
chassis), the magnetometer was only
2” from the arena floor, which
swamped the ability of the
magnetometer to read to Earth’s
magnetic field. So, they changed
over to a dual laser transmitter. One
(a visible laser) is used for sighting,
and the other (an infrared laser) for
directional information.
After prototype testing using a
simple eight bit microprocessor, they
built their “beta” version using a
DSP-based control system. The
fairly advanced 16-bit DSP processor
had all the usual motor control
peripherals: quadrature encoders
and pulse width modulation
generators, in particular. This setup
worked for them from the start. They
got some basic communications and
controls running, but the system wasn’t flexible enough for all their needs.
So, they moved to the combination of the Nios processor and Altera
Cyclone FPGA. The communications
system uses a dual approach:
802.11b for the primary system and
a robot-specific 900 MHz system for
the backup system.
Operation at the laptop is intuitive. CycloneBot can be commanded
with simple joystick input to move
north, south, east, and west.
Telemetry is passed back to the
laptop through the data stream for
real-time status checking and later
diagnosis and evaluation.
The heavy computational lifting
is handled by the onboard
Cyclone/Nios combo, freeing the
driver from the usual demanding
relative-path-based control requirements. This intent-based control
allows the pilot to focus his attention
completely on the strategy of the
match. SV
Material and photos were contributed by
Ilya Polyakov, Team Carnivore; Rich Olson,
Team Spambutcher; Michael Worry,
CM Robotics; and Dale Heatherington,
Dale’s Homemade Robots.
MAN UFACTUR IN G:
Win With Bulletproof
Planetary Gearb xes
● by Nick Martin
Most combat bot builders in the
smaller weight classes start out
using drill motors or small custom
planetary gearbox boxes such as
those marketed by BaneBots. Many
of those builders have found, as I
have, that the stress of combat will
break the gearboxes at the most
inconvenient times.
The failure is usually a broken pin
in the second stage, which leads to
stripped gears, motor burnout, and
crushing defeat. Fortunately, this
cheap and easy upgrade will fix
the problem, win battles, and save
you money.
Parts and
Resources List
You will need only a few
consumable parts, some scrap
aluminium, and a few small tools
that you may need to buy. You will
also need some gearmotors; I chose
the BaneBots 42 mm model for this
project. For major tools, a drill press,
grinder, and either a good bench vice
or an arbor press is essential.
Jig Making
This project relies on several jigs
SERVO 03.2008 31