By Jonathan Pillai
My first encounter with building fighting robots came at Alstom Gas Turbines in 1999, the year before I came to Imperial College. I was working during my year out as part of the Year in Industry Scheme when an email was sent around appealing for potential roboteers.
Meetings were held, many people came initially, but six remained sufficiently interested to take action. Ideas for two robots were tabled, a conventional 4WD skid steer design and the hitherto unheard of concept of Stinger. Much scepticism was invoked by the latter, but its originator, Kevin Scott, was sure of its validity and began planning its realisation.
The concept is in essence very similar to a toy many people may have made in their childhood, called a cotton reel tank. This consists of a cotton reel (surprise), an elastic band and a pencil. The elastic band is fed through the spokes of the cotton reel and around one end of the pencil. The band is wound up by holding the pencil and turning the reel. When set loose on the floor, it propels its self along, dragging the pencil behind until the band is unwound.
In the case of Stinger, instead of reels and elastic bands there are two wheels and electric motors, with the pencil analogous to the weapon. A key feature of the implementation is that the motors and batteries are mounted fixed inside each wheel so that they rotate with the wheel. Each wheel drives its self around a fixed gear on the axle via a planetary gear drive. This maximises the second moment of inertia (how hard it is to change the speed of something turning) against which the weapon can be operated and thus the weapon’s effectiveness. The concept of Stinger is elegant in that it minimises component redundancy, that is, it uses structures and components for more than one purpose whilst maintaining simplicity.
When I left the Stinger team after my year out, I wanted to build a robot of my own. I wanted to evolve the Stinger concept by implementing an active (powered) weapon. After settling in at Imperial, I started setting the necessary elements in place to facilitate the creation of a fighting robot, starting with funding. Having done the Engineering Education Scheme, Year in Industry, and Headstart, the first source I investigated was the RAE’s Individual Bursary Award. I was awarded £700 as a result of this. I then found out about a meeting of the Old Centralians Trust, the charitable alumni organisation of City an Guilds College, but only 20 hours before it was due to start. I prepared an application and obtained two supporting letters from members of staff with 15 minutes to spare. I was awarded a further £700, more than I had asked for. Two days later, I fell while snowboarding at a dry ski slope fracturing two bones in my right hand, which it turned out required stabilising with two titanium plates and 10 screws. This put me out of action until after my summer exams.
During this period I finalised the design of the wheel assembly. I had hoped to begin construction over the summer holidays, but fellow students who had indicated they would like to help were otherwise engaged and I found my lack of workshop training meant that finding a way to get it built was very difficult. I kept on the lookout for sponsors, and managed to get some free Nickel Zinc batteries. This is a very new technology and was a real boon to find. I also got some LDPE sewage pipe which I decided would be a good material for the wheels.
Towards the end of the summer holidays, after not having found a suitable construction environment in college, I was even reluctantly considering looking outside college when, out of the blue, I received an email from someone in the Electronic Engineering workshop. I had never realised it was there, but it turned out to be exactly the place I had been looking for. Ray Thompson and Phil Jones, the two workshop engineers, were very keen to get involved and were surprised that I hadn’t found them already.
The magnitude of the task of building a good fighting robot had become more obvious to me as I progressed. Even though I had found the base I needed in the EE workshop, I still thought it necessary to try concurrent engineering. The design lends its self very nicely to this approach in that the weapon is largely independent of the wheels. The design demands that the weapon has its own power source and radio receiver, so there is no communication to the wheels. I spoke to a member of staff in Mechanical Engineering who agreed that designing and building a weapon would make a very good 3rd year project. I drew up a simple specification, and handed it over to Chris Liston, a third year student who had been interested in the project for some time.
My task was now limited to building the wheels. Instead of jumping straight in to construction, Ray was keen for me to render every single component in SolidWorks, a 3D CAD environment. In doing this, and listening to the opinions of people with years of practical experience I was able to hone the design even further and know exactly the shape of every component, and how it would be made.
In the first week of the new academic year, I set up a table at the freshers’ fair. Many people put their names down, but I was particularly impressed by one student, Gary Ewer, who immediately recognised the Bosch GPA motors on display. Most roboteers use these. He had also built a robot in his year out, so also knew about the engineering culture of building fighting robots.
Gary and I spent quite a while in the workshop making the easier components, learning to machine as we went along. We were very fortunate to be able to do this. Most workshops would not let people with our (lack of) experience use machine tools.
This pattern of work carried on through to Easter before which time new sponsors had offered free bearings, FETs and polycarbonate. Over Easter my main job was making the axle. This was a more advanced task than other components and involved welding, which I assumed I would have to lean on someone else to do. After waiting a while, I decided it may be quicker for me to learn to weld and make it myself, so I did and it was.
It was over Easter that I heard of the possibility that the EEE workshop may be closed for relocation at the end of the summer term. Although this seemed quite ominous given that several other workshops were affected by the relocation, I assumed that given all passed obstacles, if necessary, I would be able to find an alternative and so pressed ahead with construction.
Leading up to and during my exams I stayed away from the project as much as I could to do all the problem sheets I should have done while I was in the workshop. Immediately after the exams I visited the workshop to see how things were down there. I was greeted with two excellent pieces of news. The workshop was staying put and a very important CNC job was well under way.
The floor temperature in the workshop was a steady 58OC due to the exhaust gasses from the combined heat and power plant below. When the academics who were to be moved to the site visited in the heat of summer, they realised that it was much too stuffy for them and refused to move there.
The important CNC job was a 6082 T6 piece that holds the motor, gears and main bearing. It was complicated and time consuming to make, so Ray and Phil had found it difficult to find a suitable window in the schedule for the CNC mill. Such a window had opened while I was enduring exams and one of these components was in manufacture when I walked in. This was a real milestone because once this component was made it enabled many of the other components to be assembled.
Throughout the year I had been keeping in touch with the weapon project. I gave advice where I thought useful, but had to let the group work autonomously to satisfy the requirements of the third year project. The group decided to build a hydraulic crushing weapon. I suggested that it would be difficult to make an effective hydraulic weapon within the mass I had allocated, but they seemed satisfied that they could do it.
The construction phase of the weapon occurred during my exams. I knew that it had not been finished but when I went to have a look I was still quite disappointed. It was very heavy and was quite characteristic of “old school” engineering. Most of the components were mounted on a ¼” steel plate. This approach doesn’t really use the limited weight effectively. The hydraulic pump was driven with a 37mm Æ motor via a nylon-geared drill gearbox (each of the main wheels is driven by a 110mm motor through 2 mod steel spur gears). Such a setup could not be robust enough to produce a good weapon. Indeed the flow rate produced was not even enough to overcome leakage at any appreciable pressure. I still thought these problems were rectifiable in the 5 weeks remaining, however Chris was unwilling to put in extra time, which was a shame considering all the effort he and the rest of his group had put in so far.
Ray, Phil, Gary and I had a 20 minute brainstorm session after which we decided that we would build a drum spinning on an axis parallel to the main axle, with mass to be concentrated at the perimeter. By the end of the day we had identified suitable materials in the stores.
After trying to design a friction drive for the weapon, although simple and tolerant of misalignment, it proved impractical for the space available, so chains were chosen. Rather than modelling the weapon in SolidWorks, to be expedient I did a full size drawing, cut out pieces of paper to represent the motors, batteries etc and moved them around until it looked right.
Shortly after that, Gary had to return to Cambridge for his summer placement. Ray, Phil and I worked mainly on the weapon from then on. We first made the drum and axle, then the frame, making brackets to mount everything as we went along. Gary returned towards the end of this process, three days before qualifying, his main task to put the finishing touches to the electronics. We all worked our way through the myriad final touches until it looked like we might just make it in time.
On the day of qualifying, in early August, we arrived at the workshop at 7 AM (when we are allowed in) and worked manically until 2 PM. We put Gahra in the Back of Ray’s car, and drove down to Wembley arena with ½ hour to spare. We fully assembled the robot for the first time in the car park and took it in for inspection. At the weigh in we discovered we were 15 Kg too heavy. The reason for this was that I had chosen the materials for the weapon with the intention of wasting away much of the structurally redundant metal. If necessary, any further reductions were to be made by skimming the weapon periphery.
Unfortunately we hadn’t had time to do either of these. Conversely, the wheels weighed on their own were only 500g heavier than expected because they were carefully designed and built. The Robot Wars crew decided to let us fight another overweight robot. The other robot stopped moving as soon as we hit it. We caused further significant damage despite having very poor radio reception. After the battle, the reaction to Gahra was very positive.
The designer of the house robots and head of visual effects at the BBC came over to us and commented in his opinion it was potentially one of the best fighting robots, if we could reduce the weight. We knew we would be able to reduce the weight and tried to convince the crew of this but they didn’t seem to agree.
In the three days following, we reduced the mass by 17 Kg, only having to take 1mm from the weapon periphery (900g). I then received the letter informing us that we had not been selected for the TV show.
Of course, we have continued to work on Gahra, albeit in a more relaxed and measured manner. The wheels and overall concept of Gahra worked better than I imagined. The weapon does swing over against the inertia of the wheels. Even though the maths predicted it would, because the weapon was so much heavier than that of Stinger, I was still not sure that the torque required could actually be met and born by the keys holding the gears to the axle.
We are currently concentrating on refining all the fittings and detail that was rushed at the last minute as well as using counterwound toroidal helical antennae to Improve reception. Eventually we will design and remake the weapon chassis. Although functional and adequate, the current weapon incarnation is not optimal due to its hasty creation.
The project continues and now that we have a physical incarnation of our ideas and work is attracting much more interest and there are many more avenues of destruction to explore.