Robot Wars Home Page Southampton University
Robot Wars 1999/2000

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PAGE INDEX
INTRODUCTION
WEAPONS SYSTEM
DEVELOPMENT
ARM PROFILE
DESIGN & MANUFACTURE
ARM MOVEMENT
ARM MOUNTING
CONCLUSIONS
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THE ARM
INTRODUCTION
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 operation.

Before any detailed plans could be drawn up, a choice had to be made over how the weapon would be powered.


WEAPONS SYSTEM
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 hydraulic systems.

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 effectiveness.
DEVELOPMENT
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 weapon.


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 arm's development.


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.


ARM PROFILE
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.


ARM MOVEMENT
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.


ARM MOUNTING
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.


CONCLUSIONS
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.


THE ARM