Many ideas were considered for the
construction of the arm. Originally conceived as a large multi-jointed structure mounted at the
rear of the robot, with a preferred weapon, a jackhammer or rock-breaker being located at the
tip. It was also envisaged that a crushing mechanism would be introduced into the arm's
Before any detailed plans could be drawn up, a choice had to be made over how the weapon would
Several different operating systems were considered to allow the arm to move. Chains driven by
electric motors, pneumatic systems and hydraulic systems were all carefully evaluated. Chains
seemed unlikely to transmit the required power, and could only be effectively used to locate
the arm over an opponent. After investigation, the potential for an electric driven weapon
seemed low. The decision was therefore reduced to a straight choice between pneumatic and
The group researched the benefits of both pneumatic and hydraulic weapons. The process included
browsing a number of websites, and posting questions that other web-users were able to answer
along with hard literature research. The consensus was that pneumatic weapons were the most
appropriate for the purpose. This is born out by the prevalence of pneumatic weapons featured
in the television show. However, after deliberation, the group decided to take on the challenge
of producing a workable hydraulic weapon. This conclusion was reached partly by considering the
group's intention to produce a weapon that is both unique and truly effective.
The major characteristics of hydraulic and pneumatic weapons are listed below in the figure below.
The group concluded that the most effective form of weapon in the Robot Wars television series
appeared to be high power weapons. Conversely, weapons that are based on high frequency strikes
or high rotational velocities tend to become jammed too easily. Once jammed, they often remain
disabled for the duration of the contest. The group decided that the most effective approach
would be to produce a weapon that would be virtually impossible to jam. The cost, complexity
and weight of hydraulics were considered surmountable problems in the pursuit of maximum
The original concept sketch of the robot (figure 15.1) shows a long arm starting from the back
of the robots' chassis, and protruding forward to the front of the robot. The arm was expected
move about pivots at various points, and to use up to three pistons to locate and actuate the
Requirements on the arm changed after the decision was made to use hydraulic power systems.
Additional cost and weight of hydraulics forced the arm design to be altered so that it
included only one pivot point, with the arm mounted near the front of the robot's main body.
The change in location enabled significant weight and cost savings in material and allowed a
more spacious area in the body in which to fit the hydraulic pump and fluid reservoir. The
bending stresses caused by the weight of the arm were also reduced because it was moved forward
on the robot. The figure below demonstrates some of the arrangements that were examined during the
It was calculated that the arrangement shown at the top-right of the figure above was the most
suitable for the task. The arrangement allowed a wide range of attack angles from almost
horizontal to vertically downward and beyond. It would also allow the piston that moved the arm
to be protected behind and above the arm.
In order to negate the potentially damaging vibrations caused by rapid firing weaponry, the
weapon was changed from a rock-breaker to a "semi-automatic" hydraulic punch. The punch is
actuated by a hydraulic piston. It is very powerful, but needs to be moved in and out on
separate manual commands.
Before the arm could be designed in detail, agreement had to be reached concerning the exact
attack positions required. These needed to be considered in tandem with the design of the
robot's ramp, which was intended to act as a platform upon which to attack opponents. The
specification was drawn up as shown below.
The exact positioning of the hydraulic pistons within the arm depended upon their dimensions and
stroke lengths. CAD software was used to represent possible combinations of extended and
retracted pistons, pivoted about various points within the arm. Figure 15.5 below shows the
geometric drawing that was used to calculate the positions of the pistons in the final design.
The arm can be rotated through an angle of 60°. The extremes of rotation are from 15° behind
the vertical to 45° in front of the vertical.
DESIGN & MANUFACTURE|
It was necessary to produce the arm in two parts, each made as a box section from 1.5mm thick
sheet steel. The larger part is attached to the chassis and protrudes both forwards and upwards
from it. A second part is housed within the first, and rotates about a pivot that runs through
both parts. The construction method of the arm is shown below in the two figures below. For the
production of both parts of the arm structure, steel sheet was cut and folded into four plates. These plates form the front, back and sides of the arm's parts. The plates are joined together by a series of spot welds. Slots are cut into the arm to allow the parts to fit together and rotate freely.
Two hydraulic pistons provide the arm movement. The ends of the pistons need to be kept static in relation to their housings. To allow
this, the pistons are provided with 16mm diameter holes at the three ends that require fixing.
(The piston that carries the chiselled stabbing tip is threaded at one end. It therefore
requires just one pin hole). Pins made from silver steel were manufactured to run through the
three holes in the two pistons. The arm structure also required holes to allow the pins to run
through the entire arm. The pins therefore provide pivot points for the pistons to rotate about.
The positioning of the pins is illustrated in the figure below, showing the layout of the arm.
A secure mounting system between the arm and chassis is core requirement of the arm design. In
order to achieve this an open box structure was bolted inside the front of the chassis. The
base of the arm fits inside this box, and can be securely fixed by a bolt that runs through
both the box and the arm. This system has the benefit of allowing the arm to be removed from
the chassis at any time, although the hydraulic cables would need to be detached for complete
separation. The integration of the arm and chassis was of paramount importance, and it was
achieved very smoothly because the two elements were designed in parallel at all times.
The arm has been produced to meet all of the requirements placed on it, although it differs from
the original concept. A crushing mechanism excluded due to the enormous strength required by a
crushing arm - which would have added too much to the arms mass. No rock-breaker is employed
because excessive vibrations may have caused problems. In addition, the mass of the pistons
means that only two were employed instead of three.
However, the arm is very strong, benefiting from both a box section construction and the
excellent mechanical properties of steel. The arm is light enough to be firmly held in place by
the chassis. It offers a wide choice of weapon tips, a great variety of attack angles, and
enormous power. Its manufacture and construction were quick, simple and cheap.