8.0 CENTRE OF MASS ROBOT
During the study of walking robots a
completely different method of walking locomotion was derived. Chapter 2
mentioned how very few robot designers ever moved the centre of mass of their
robots. This was opposed to the findings in chapter 3 where almost all animals
even insects moved their centre of mass. It became apparent that to move the
centre of mass, allot, could be very advantageous.
By using a moving center of mass, a
completely different SCR is developed.
The reasoning was based on making the
simplest possible walking device. The design is shown in figure 8.1 Joints A, B, C & D are actuated.
Figure 8.1 lay out of COMR (Centre of
Mass Robot)
Figure 8.1 continued
The method of locomotion is as follows.
1) move mass to one end such that the sum
of moments around pivot A is 0 or slightly -ve around A.
2) Cause actuator at joint A to rotate to
desired position (this raises foot 1)
3) rotate joint B to through desired angle
4) remove actuation force at joint A
5) drive counter weight to other end
6 )repeat this process with the other
foot (foot Q)
A demonstration of this is supplied in
the second segment of the Video.
This process allows the robot to climb to
two surfaces within the range defined by the angle of incline and length
between the two feet.
A prototype was built out of Technical
Lego and tested.
This approach has some major advantages
over conventional walking robots.
1 There is no complex leg placement.
2 walking around corners is very easily
achieve as the robots next step can be in any direction, this removes all the
complicated leg Co-ordination, for turning corners or through any angle.
3 The vertical height that the robot can
achieve is quite remarkable when compared with other small and even large
robots, it easily out performs any comparably conventionally sized robot .
4 Almost any surface could be
accommodated by allowing three screw
type feet on each foot.
5 The power supply was part of the pay
load, it was made into a useful component instead of a liability, as in most
robots. It serves as part of the counter weight mass.
6 Climbing is very efficient, their re no
complex positions that the body has to assume to keep balance.
7 There is lots of scope for development.
This model is only a prototype. The practicality of the idea is demonstrated in
the time it took to implement, which was about 3 hours.
8 Control systems and strategies, would
be much simplified, due to the reduction in d.o.f and the way in which this
type of robot navigates terrain.
This robot design achieves walking, and
the tested robot can almost climb a step.
Its limitations stems from the physical
layout of the robot. That is the counter weight, when at one end limits how
close the robot may move towards a wall. A dynamic running motion would be hard
to achieve., but again wheels could be used on the feet to drive over smooth
terrain.
This entire idea is quite a radical
departure from conventional robot designs, however it demonstrates an
alternative method of type 3 terrain navigation. Several advances could be made
to improve the robots performance.
1) Use a heavier counter weight.
2) Redesign the robot so that is can
rotate to the position shown in figure 8.03.
3) Make the connecting beam element 3
telescopic, this would reduce the distance the counter weight has to travel
climb small distances, thus making the robot more efficient.
4) Make the robot lighter, use aluminium
and carbon fibre elements instead of Lego.
5) Redesign the robot such that one foot
may be place vertically over the top of the other foot.
By combining improvements 3 ,4 and 5 the
counter weight and thus the total power consumption of the robot may be greatly
reduced, as well as improving the maximum height that the robot can climb. It
would be quite feasible to make a robot of similar proportions to the six
legged robot able to make a vertical step of over 1 m. See figure 8.2 to see how the turning circle can be reduced to the
size of the base foot. Figure 8.3
shows how the improvements would argument the COMR's vertical performance.
Figure 8.2 .This shows how the turning
circle may be reduced to the size of the base foot
Figure 8.3
shows how the improvements could argument the climbing ability. (1) The feet
are place vertically in line and the telescopic tubing is also vertically
aligned, this is to avoid buckling upon extension. (2) & (3) The telescopic
tubing is extended (4) The upper foot is place. (5) the counter weight is moved
to the upper platform. (6) & (7) the lower foot and tubing is retracted to
assume the position in (1) again.
The pay load of the robot would be
accommodated as part of the counter weight and feet. To compensate for a change
in payload the counter weight would vary the distance it travels beyond the
pivots.
The success of this method warrants further
investigation of this approach to a walking robot. It yields a solution that
circumvents many of the traditional problems that robot designers have faced,
such a gaits and leg design.
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