Construction of the ScratchGPIO Dalek – Invasion part 2

Here’s the second installment of the ScratchGPIO Dalek – the first part can be found here. My apologies for the poor quality of the photos. Our camera was in use elsewhere so I only had my mobile. I’ve discovered that it can’t cope with low light and close up shots. Perhaps I should have used the Raspberry Pi camera?

MostOfTheBitsHere’s what I’m starting with. I’ve got a servo, some LEDs (red and blue), Chromed LED bezels and a few bits of plastic cut on a CAM router. The Dalek is a plastic container originally for bubble bath,but having removed the bottle it seems that there’s plenty of space for a circuit board, a servo and some odd bits of wiring.

EyeballThe eyeball LED is made from a piece of chromed brass tubing removed from an old telescopic aerial. The LED is soldered to the end of stranded wire and carefully sealed with hot glue. A clip-on LED bezel is used to complete the effect and makes for a realistic eyeball. I would have liked to add on some disks half-way along the stalk, but I didn’t really have time and perhaps it can be easily overlooked?

The head lights are made from blue LEDs soldered to the end of stranded wire and then pushed into some chrome LED bezels that were in my parts stock. At first, the LEDs were difficult to see as they are so directional and the bezel tended to shield the light coming out sideways. The solution? Fill the bezel with hot glue (in fact, overfill it) and then let it cool without disturbance. This created a slightly domed translucent light which can be seen from all angles. For such a simple solution, I’ve been really impressed with the result. And I didn’t burn my fingers. The domed lights are then pushed into the head. The slightly rubbery nature of the head means that I’m unlikely to need to put the nuts on the other side of the bezels. I don’t think I’d succeed either!

BufferboardThe bufferboard is one of my own designs (more information here) that I produced a while ago. I use it as I managed to kill a couple of Raspberry Pi computers while experimenting with servos. I’m not sure whether it’s a faulty servo that did it, but ever since I’ve been quite nervous to work without this board in the way. It also level shifts the outputs to 5v instead of 3.3v, making the LEDs (particularly the blue LEDs) able to run at their full brightness. Having said all that, I’ve used a 330Ω resistor in series.

ServoWheelThis part is a simple three-spoke wheel that fits on top of the servo horn. The outside diameter has been chosen to fit the inside hole under the dalek head. The three spokes gives plenty of space for the wires to pass upwards from the base. I had pondered how to get the servo horn to stay attached as I’ve found hot-glue to be a bit unreliable on these and there wasn’t really room for the M2.5 screws that I usually prefer. Cable ties to the rescue! They hold well, especially as I filed a few little slots in the servo horn. Simple and effective.

DalekbaseFitting the servo up inside the base was a bit more tricky. There are quite a few obstructions up inside the base which have to be taken care of. In the end, I cut out the top section carefully and then used added a foamed pvc plate which carries the servo. After nearly exhausting my supply of M3 screws, the servo was mounted and the horn fitted.

TwoPartsOfDalekHere are the final two parts ready for fitting together. The cables will pass down through the wheel into the base where they are then connected to the buffer board with 330Ω resistors. The servo is also connected. I ran a little test routine from Scratch to ensure that the servo can reach both extremes and also find the centre. Once this was done, a few blobs of hot glue ensures that the head and the wheel are joined.

Coming up… programing the Dalek with ScratchGPIO (and Python eventually).


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