To get the ball rolling we designed and constructed two of our own "company"
robots. The robots we made are not meant to be the best design for the
ultimate boxing robot. We wanted to build a couple examples of this class of
fighting robot with the least amount of work in the shop. Building an
eight-foot tall Real Steel-type boxing robots like the ones in the
Robot Combat League are too much for the
average team to commit to. Roboxers are a smaller alternative.
We used a lot of water-jet cutting and a standard
BattleKits base to
keep the build time down. Another time-saver was the use of several
off-the-shelf extruded aluminum square tubes in the arms, legs, and hips.
Almost all the components are available from either
These robots put up a good fight but a different design from a clever
builder should be able to spank these things. Keep in mind that this is not
the only way to build a robot! You are welcomed to use any part of our
design that you like but our purpose in posting this is to help you use our
experience to come up with a new, different, and hopefully better design.
picture shows most of the tricky parts of the robot. We used
an all-electric design to keep things simple.
To get a
sense of scale, note that the hips are 15 inches wide and
the sprockets in the upper chest are 5 inches in diameter.
The robot stands just over four feet tall.
The upper body is divided into four distinct areas, each
of which houses components that provide a different
function. Below are descriptions of each area.
Starting from the lowest level, here we see
the electric linear actuator that flexes the robot's hinged
spine. Most of the actuator is hidden inside the robot's
"shorts". We used a
Motion Systems actuator that has a unique and very
useful clutch that disengages at the ends of the travel.
This eliminates the need for limit switches and it also lets
you use full power right to the ends of the travel without
damaging anything. When the actuator reaches the end of the
travel it simply stops while the motor continues spinning.
This same type of actuator was used in another one of our
robots - BattleBots champion
We liked the idea of disengaging the motor
at the ends of the travel so much that we also used it in
our punching mechanism, (details below).
This picture shows the single electric motor
that powers all the punching action. We used the
AmpFlow motor for its light weight and extreme power.
The motor power goes through a two-stage speed reducer made
from #25 chain and sprockets. The speed reducer has a
heavy-duty design using 3/8" thick aluminum plates because
it serves triple duty as 1) a speed reducer, 2) a mounting
point for the spine hinge and linear actuator, and 3) a
mounting point for a 7/8" central shaft, (not visible in
this view), on which the rest of the upper body is mounted.
Keep in mind that the central shaft is fixed
in place and does not turn, yet there are a total of six
power transmission elements either fixed to the shaft with
keys or riding on bearings on the shaft, (four sprockets,
one gear, and one friction wheel). The shaft is keyed to the
body of the speed reducer and it runs all the way up into
the head. It does not turn but all the power of the motor is
ultimately transmitted through that shaft. How is that
possible? Details below.
After the power passes through the two-stage
reducer it goes into this section of the torso. In order to
get realistic punching power from our single electric motor,
we felt it was important to come up with a design that would
enable us to use full power right to the ends of travel.
Here is a view of the mechanism we came up with.
The power from the motor goes into the
little red urethane drive wheel on the right. It presses
very hard on a big aluminum friction wheel that has a flat
spot on it. The aluminum wheel makes only one rotation when
the robot throws a punch. When the flat spot reaches the red
drive wheel it disengages and the drive wheel and motor spin
freely without jamming up the mechanism.
This set-up also does double-duty as a
torque limiting device. If the arms get jammed, the urethane
wheel slips and the motor will not stall.
The aluminum friction wheel spins freely on
the central shaft. The motion from the wheel then goes
through another three-stage speed reducer that is made from
#35 and #40 sprockets and chains. The large sprocket in the
final stage of this speed reducer is keyed to the central
Not only does the friction wheel spin freely
on the central shaft, the entire torso above the first
two-stage speed reducer also pivots on that shaft. This has
the effect of rotating the upper body left and right by 25
degrees each way as the friction wheels rotates one
revolution. When the robot throws a left punch, for example,
the shoulders and upper body rotates left to get maximum
power behind the punch with very human-like motion.
The red drive wheel is fixed to a shaft that
passes through a curved slot in the aluminum plate. The slot
and the flat spot on the friction wheel are visible in the
above picture if you look closely. The only thing holding
the upper and lower sections together is that central shaft.
The head is also keyed to that non-rotating shaft so it
always points forward. The robot always "looks" at his
opponent even as his arms are swinging and his chest and
shoulders are pivoting back and forth. This is another
design element that adds realism to the action.
The same motor that pivots the torso also
powers both arms. Take a look at the above picture to see
how this is done. The central shaft continues up through
this section of the chest. Since the upper body moves
relative to this fixed shaft, it is possible to pick up that
motion and use it to drive the arms.
Three large bevel gears take that motion and
send it off at an angle that gets it to the shoulder joints.
The central bevel gear is fixed to the non-rotating shaft
with keys. The other two bevel gears pivot around the fixed
gear in a planetary motion as they move with the pivoting
torso. A large sprocket transfers the resulting rotation to
smaller sprockets in the shoulders.
Also visible in this view are some
electronics that, (among other things), flash a strobe on
the top of the head when the robot is struck. The central
shaft is hollow and some of these wires pass right through
the shaft to get into the head and down into the lower body
without the possibility of getting mashed in the gears and
chains. Thanks to teammate Dave Andres for his work on the
Inside the "H" shaped blocks are 2" long
springs that absorb the arm's momentum at the end of the
travel. Only a short length of the springs protrude from the
blocks. The springs are kept in place with urethane bumpers
that are screwed on to shoulder screws that pass through the
The sprocket in the shoulder joint is fixed
to the upper arm so the whole upper arm rotates along with
the sprocket. The final step in this convoluted path of
power transmission is getting the forearm to move. That is
done with one last set of sprockets and a chain, (visible in
the elbow area). The number of teeth in all the sprockets
was carefully chosen to provide the correct range of motion
in every joint.
There are a total of six stages of speed
reduction, (and torque multiplication), to get the 6000 RPM
of the motor down to a reasonable punching speed. The final
gear ratio is 183 to one. Ignoring the slowing effects of
friction and inertia, this works out to about four punches
When one arm extends to throw a punch, the
other arm retracts. The chest and shoulders pivot in the
direction of the punch while the head keeps looking forward.
One motor actuates the pivoting chest, both shoulders, and
both elbows, while the other motor in the linear actuator
flexes the spine to aim the punches up and down. That is a
lot of motion from just two motors. We did it this way to
keep things simple, reduce the build time, and make
controlling the robot easier. Good robot builders will find
ways of using additional motors and possibly pneumatics to
make more powerful and effective boxing robots.
Here is a view of the rolling platform. It's
BattleKits base. One of the keys to getting this all to
work is to put as much weight as possible into the base. The
robots are tall and if they get too top-heavy they will have
a tendency to tip over. The components in the base include
AmpFlow E30-150 motors, Two AmpFlow motor controllers, and
four 13Ah batteries. Everything is connectorized using