Tuesday, 17 January 2017

Light up Lego continues

There's a very special little person having his fifth birthday in March, so there's a few weeks to finish this one. But then again, having a few weeks leadtime often means leaving it for a while and not worrying about even starting it, and before you know it, you're up til 3am the night before the deadline and nothing's quite working as it should....

But this is going to be a light-up Star Wars Lego set of characters. At first it seemed easy - stick some 0805 LEDs around the place, a few resistors, connect up power and ground and off you go. But as we started to put together our first character, things starting getting trickier.

Firstly, we can't just put power and ground - one up each leg - and hope that a 5-year old understands direct voltage polarity and why sometimes some things light up and sometimes they don't.

As we already had a blue light sabre, it made sense to start assembling Luke Skywalker. The first thing was to drill "up" the arm, from the wrist, towards the elbow.

Because of the bend in the arm (and because our drill bits are perfectly straight, not bent half-way along!) we couldn't get the channel to go perfectly from the wrist up to the shoulder (as we would have preferred). The best we could manage was to come out just below the shoulder joint

Which meant that this arm isn't going to move all that much (we might even glue it to the body just for good measure). And a matching hole had to be made where the arm meets the body, just under the shoulder socket.

We cleared out the body cavity (to make a little room for the sot-23 rectifier when it arrives)...

... and pushed the wires from the lightsabre up the wrist and out of the shoulder.

We then re-assembled the light sabre into the hand, the hand into the wrist and the arm into the socket. As this is a dry fit, we just left everything clicked into place. Eventually all of these pieces will be glued, to make the character much more robust (and hopefully more likely to stand up to the rigours of being played with by a five-year-old).

As there's no rectifier yet, we had to make sure to get the connections the right way around for testing.

Lego Luke and his blue light-up light sabre.

At first we thought connecting to pads in the feet (which in turn connect to the studs in the Lego) would be easy. But we'd forgotten that kids like to actually play with their toys, not treat them as fancy models to be admired. One thing that we definitely couldn't get away with (despite our protesting to the kids parents about how hard it would make the whole project) was simply gluing the legs on.

Kids want to sit their Lego characters down, put them inside Star Wars space ships and run around the room with them - not place them on a dedicated plinth and admire the technology and dodgy hand-soldering of tiny surface mount parts that make things light up. Which means we had to keep the pose-able legs.

As we only had one set of Luke Legs, we tried a couple of ideas out on some spare minifigs before hitting upon a solution with a left-over C3P0 (the pearlescent one, not the cool one with the ultra shiny chrome paintjob).

An example of "powered" Lego studs

When our Lego character is on a powered base, connection pads in the feet will make contact with metal studs pushed into the surface of the Lego bricks.

Running wires from the body into the legs at this point is easy. But when the character sits down, with the legs folded out in front, either the thin magnet wire will stretch (and possibly snap) or will get snagged up again when the legs are straightened out. What we decided on was tiny pins connecting the bottom of the body to the top of the legs, with any "loose" wire contained within the leg.

So we drilled a hole from the top of the "hips" (with the body part removed) into the tops of the legs. Then, put the character into a sitting position and drilled through the same point in the hips - this time into what would become the front of the legs, when the character stands up. Then simply cut away the excess between the two points

(this photo was taken after completing C3PO to demonstrate the technique on a different character)

The end result is a character with little slots in the front of their legs. It's a good job Lego Minifigs are so stylised that it doesn't really distract too much from the characterisation of the person it's supposed to represent.

When added to the character, we have legs that can still move from standing to sitting, while maintaining a short length of solid-core wire between the top of the leg and the base of the body

The leg is allowed to move without bending or stretching the solid core wire

We're still waiting on our rectifiers (Farnell have them on back-order, due around about the 19th/20th Jan) and pads for inside the feet. So it's difficult to build an entire character and try one out fully. But in the meantime, we've got a Darth Vader that needs a red LED light sabre, an Emperor wanting some edge-light acrylic cutting for his lightning-hands and a C3PO that needs wiring up to see if we can't make his eyes light up. So plenty to get on with for the rest of tonight at least....

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