The
Robots
Omni-Bot & Axi-Symmetric Omni-Bot
"Omni-Bot", a six-legged omni-directional walking
robot ....and...the latest walkingrobot, the "Axi-Symmetric
Omni-Bot" (picture on the right).
Both robots are tetherless (=no umbilical) and weigh 2kg.
They use eighteen, high performance, S9450 Futaba servos.
"Omni-directional" means that the robot can
walk in all directions including rotating whilst translating
like in a Viennese waltz. Furthermore, the body possesses
6 degrees of freedom i.e. the body can rotate and translate
(albeit limited) about and along its fore-and-aft axis,
its athwartships axis and its vertical axis. This means
that the body of the robot can be a stabilised platform.
For example it can stay level and/or at a constant height
(within limits) whilst walking over uneven terrain. Thus
when we fit an on-board computer vision system, the image
can be kept stabilised, similar to our own eyeballs which
stay level even though our heads are moving. It's also
similar to the head of a bird of prey that fixates its
head (eyeballs can't move with respect to head) on an
image even though its body is shifting.
Both robots use the same leg module. The one on the
left has exposed areas for addition of a gripper. The
one on the right has its leg loading more evenly distributed
but still has enough room for accessories. The one on
the left will be programmed as a cunning stealthy predator
whilst the one on the right will be programmed as a
fleet-of-foot prey. We now have an, in-house designed
and built, vision system that shortly will be fitted
to both robots. The vision system can recognise circles,
squares and isoceles triangles together with the orientation
angle of each shape, the size of the shape, and the
location of the centre of the shape. Hence we have the
basis of identification marking of landmarks and robots
thus enabling a goal-directed behaviour robotics system.
We have ten Omni-Bots, and shortly will have ten Axi-symmetric
Omni-Bots. We want these twenty robots to carry out
team behaviour such as following each other in single
file.
An instantaneous centre of rotation is specified before
each step is taken then Omni-Bot rotates cw or ccw about
that point. Because it is an "instantaneous"
centre of rotation it can be continually updated before
each step. This is what gives the robot the property
of omni-directionality and also the ability to develop
complex behaviour patterns. The angular position of
18 servomechanisms, that actuate the six legs, are calculated
50 times per second by 9 Basic Stamp2SX microcontrollers
using only integer mathematics and not using sin, cos,
tan, arcsin, arccos arctan or square root. Instead,
specialised, highly efficient, realtime algorithms have
been developed that only use 16bit multiplication, division,
addition and subtraction. Look-up tables are avoided.
Instead, polynomial equations are used.
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