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This is another one of those can be made at any times parts, as though its not so important, I need anything that will move or extend to be finished around the same time as the main body, as those parts will have to be placed so a frame can be made round them. So I had a bash at this bit.
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So as always if you have looked at other stuff I have made, I start with a rod of resin cast to nearly the correct size. The first job is to face it off, so the surface is smooth and the diameter even the entire length of it.
With that taken care of its time to mark out the sections to be machined. Having the plans already drawn up saves a lot of time. In the past I have had to extrapolate measurements from pictures using a known size, and then calculate the rest from that, while a very positive way to obtain precise measurements its very time consuming. With the measurement pre done, is just a case of transferring them across to the resin rod.
With the main arm section nearly done, it was time to start thinking about moulding and casting it. This is actually a very important time, as making something to large or awkward makes it very difficult to first make a mould of then secondly cast.
To start with the end section has to be able to slide out, so a thinner section of tube will be needed for this, so that has to be considered in the moulding and casting. As this was going to be an easy shape to cast, but a tad heavy, being so much resin, I decided to use a length of hollow copper rod to run through the middle, and then affix the sliding mechanism to that. Not only does it make casting easier, it also allows for the sliding mechanism to be carefully constructed outside the arm, then glued in place when right, but saving weight at the same time.
To affix it to the end part which it will pivot on inside the body, a large threaded ring is added, so when moulded and cast, the thread will be cast into the main arm. It will also have the hollow copper rod at the centre for added strength.
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It was now time to start on the end section that extends. However I always watch the film I am making something from frame by frame on DVD as this allows for spotting extra detail. In this case I watched the part of ANH when Luke and co are trapped in the trash compacter after escaping the cell block, and R2 uses his interface arm to stop the compactor squashing them.
Using a vernier gauge to take measurements from the screen, I noticed a few discrepancies in the end bit, when comparing the measurements on the plans and the dimensions on screen.
As I was going more for on screen accuracy, I made a couple of alterations to match the screen. I always thought when just looking at the plans and the screen, the very end bit was to short just to the naked eye. No harm done, and with that sorted it was back to machining it.
The end bit took a bit more time as a few angles were needed, and not having every angled cutter there is a few careful cuts were needed to match up. Came out alright though.
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Next was the end pivot. This needed to screw onto the main arm, but have an offset pivot so when pulled downwards on with a cable the arm swings up to the horizontal position. I know some use compressed air, and some a small motor attached to the arm, but I wanted all accessories cable operated. The reason for this is cable can be run through tube, so the motor and mechanism operating the arm doesn’t have to be anywhere near it. This allows for more arms or accessories closer together without having to worry where the motor will be.
With a bit of trial and error the angle is worked out, and the pivot arm fitted. This will have a custom made bracket made out of carbon fibre to attach to the main frame when finished.
Next is s bit of fine detailing in the end piece. The end layout is as per the plans but I altered the side section just a tad, so I could incorporate four steel balls to look like electrical contacts when glued in place. I will place brass rod in the tubes on top to also resemble contacts.
The last picture shows the arm completely assembled. When finished the end will shoot out via a solenoid and cam to get the correct length, to look as the film one did.
The work on this page is ongoing, so the page will be updated as it progresses :)
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