Lit A-Wing Engine Mod

I was asked if I would like to post a guide on how I made my lit A-Wing model, and I said sure. I had fitted an A-Wing with lights in the engines, for a gift, and the wires almost entirely internal to the model. As a first run/attempt, the model is permanently attached to the stand, so to get pilot token must be split to slip onto the base. I have a few custom bases made to get around this, but I have not entirely worked out the tiny connector required to make it work.

The original in question:

A-Wing Lit

 

I am writing this guide with the assumption that you may not be familiar with everything I used, regardless of how common it may be. I would like anyone with determination to sit down and give this a try. So to get started you will need the following tools, materials, and a great deal of patience…

 

Tools required:
– Pin Vice (Half vice, half drill)
– Drill bits from #80 up to 0.1” (possibly a touch larger, when drill bits get really small they start to designate them with numbers instead of the fractions, the bigger the number the smaller the diameter. A #80 is a smaller drill bit then a #20, charts of exact decimal equivalents are easily had on-line)
– Flush Cutters
– Soldering Iron and more importantly one where you can control the temperature, ideally with a fine tip like 1 mm to 2 mm or so. This depends on largely how good you are with SMD/SMT electronic components, I can easily get by with a large tip because I work in the electronics industry. So hand soldering tiny things with incorrect tools is not a problem for me, it may be really challenging to you. Remember to make things aas easy for your self to start. The temperature setting will give you a greater chance of not destroying the LEDs you seek to install.
– Tweezers
– Hobby knife, fresh blades make all the difference.
– Helping hands style clamp (optional)
– Plastic jewelers loupe, this is that little one-eye-magnifying-glass in the old cartoons they woulduse to examine gems. Inexpensive and versatile for so many tasks.
– Paint brushes, there will be touch-ups.

 

Materials:
– A-Wing model
– Paint for touch ups
– Epoxy putty, to fill gaps.
– Super glue
– 2x 0603 LED, ideally amber coloured for authentic A-Wing engine glow. For those not familiar with the 0603 designation, it is a size delimiter and there is an imperial and metric 0603. I used the Imperial size (0.063” x 0.031”). It is about a grain of rice in size, possibly smaller. Get more if you have never done this and need practice, very inexpensive. I used “475-2712-1-nd” from Digi-Key. Digi-key is a massive electronic component supplier and I do not mind paying the shipping for generally what is the best and cheapest selection (their parametric search is just excellent).
– A CR2032 coin cell battery holder, I used the “BU2032M-BT-GCT-ND” from Digi-Key as well.
– A CR2032 coin cell battery for said holder, there is a variety of coin cell batteries but that size is common and in terms of power and size it worked best for the limited space under the base.
– Some resistors capable of handling the power being put into them. They may be 0805 or 0603 in size depending on how you size them. I was using two 1000 ohm resistors in parallel to get 500 ohms, as it is what I had on hand. Ideally you want two resistors, one for each LED and I will get into all that in this guide.
– 36 AWG wire, it is hair thin and also known as magnet wire. It generally is coated with a clear insulator. It won’t handle much current but it is more then we need. I was not running this near full brightness and it is bright.

 

Model Information:

First we need to figure out how to get wires through the model. Having worked with injection molding machines, I have some idea of how the models could be made. Depending on geometry and/or cost, they will be either solid, hollow or some combination.

As I suspected with the A-Wing the body is hollow but the engines are not, and likely glued on after the fact. The stand is acrylic or closely related, which is a bonus. What the model material is I am not sure, definitely a soft, inexpensive plastic. The peg that is in the body for the stand to fit into appears to extend inside the body, possibly with some sort of flange that is embedded into the plastic of the body. There may be some sort of internal body support plate between the peg and the engine area. I may have misjudged the size inside as it is really small. It is hard to tell but it appeared some wires got caught on something as I fished them through.

So where does this leave us? Well, we could take the model apart and make the wires entirely internal, but we will probably wreck it beyond repair if we did. If the following is not entirely clear , the next section goes into detail and has pictures as well. Well the easiest method (and the method I choose) is to glue the LEDs right onto the engines in the nacelles themselves. They blend in at a distance so no one will notice them when they are off. From there I would route the wires around the engines to the bottom corners, drill part way through engines until I just past the back plate of the A-Wing. At this point I would drill into the corner of the A-Wing nacelle where the nacelle, back plate and bottom of the model meet, this will provide an exit from the hole we drilled into the nacelle out to the back as close to the model as possible. Then drill into the back plate in the same area. This allows the wires to go through the engine, out the side of the nacelle and immediately into the model. After that, we drill right into the mounting peg straight into model cavity. Basically, you want to drill straight and through as few (ideally hollow) pieces as possible.

 

Drilling:

This is either the most tedious, or second most tedious, aspect of the mod. Patience is required. It is easy to go off course and have holes where you do not want them, or worse yet snap a drill bit. The bits at this size are very thin and if you break it off inside the model, you are done. If you go off course, you can probably straighten the hole out but it’s going to be such a pain. Once I had the bit started I just watched TV and slowly drilled out the model.
So I drilled my holes basically one of two sizes, one that was a few wires diameter in size and the other about the size of the hole in the stand peg. By this I mean, if you look at the bottom of the A-wing there is the tube for the stand. It is a wedge shape and I drilled out most of that wedge shape.

First I drilled into the engines. The bit size was tiny, #74 or similar. Looking at the back of the A-Wing right side up. The right engine was drilled between 6 and 9 o’clock. The left engine was drilled between 3 and 6 o’clock. You want to drill further then the point of where the wire will come out. This makes it easier to push extra wire into the body to fish out. You could drill to where you drill the holes in the next step and the wires in theory would pop out the side… but I doubt it.

Engine Holes

The wires actually peek out in the corners where the nacelles intersect the body on the rear of the model. You drill perpendicular to the hole you made as close as you can to the back plate of the A-Wing.

Nacelle Hole

Then drill into the back plate of the A-Wing in the corners as close to the hole in the nacelles as possible.

Back Plate Hole

Drill into the stand peg using a 0.1” bit, it will take some time to actually get fully into the body, the bottom plate/body is rather thick. Once that is done, using the hobby knife or flush cutters remove the peg from the body. You want to save this piece. There will still be the piece inside the body, I used a hobby knife with a fresh blade to cut it out, some was left floating in the body, some was removed.

Bottom

Drilling the stand pipes, use the same bit as you did for the stand peg in the model. Take your time so that you are going straight through the entire length. It is tedious but easily doable. The difficult task is when you reach the peg on top of the stand pipe. I actually partially drilled those out, that way I could keep them to glue the pipes together and more structural stability and was entirely worth the hassle. I had to press on the peg a bit because they want to bend or move out of the way of the bit and break off. If you can do at least half the peg that is great. Clip the top of it off.

For the base itself, use the same bit as above and drill out the center peg as best you can from the bottom. Once done just clip the peg off. From the bottom using the soldering iron (some people are going to hate me for this) melt a shallow channel from the hole towards the front of the stand. This is so the wires can come in and we can glue the battery holder over the hole so the model will balance on the battery.

 

Wiring:

This is the most tedious bit, or second, that took me sixteen or more hours.

Cut four pieces of 36 AWG wire about 6 or 8 inches long. Length is good, the ends are going to get screwed up and damaged during fishing/routing and you want to cut those parts off. Remember, removing material is much easier then adding it back.

So, you are going to do this four times ever so slowly. Stick with it, it can be done.

Fish the wire into the nacelle and out the side. The trick is to use a very tiny drill bit, like #78, to go into the side of the engine, hook the wire and pull it out. I have no magic technique to impart upon you, it is just work you must soldier through. Once that is done push the wire into the back of the body. Aim for the center of the model and then fish it out the bottom. Again, this is tricky. It is tedious and there is no easy way to do this that I could find. In retrospect if you have dental tools available to you, that may work out really well, though I could not get a pair of small tweezers in there and the wire is hard to grab. Put a small piece of tape on both ends of the wire and give them the same, unique, designation. It is important to know which wire is which as LEDs have a polarity (meaning they need the electrical current going in a certain direction to light).

Then repeat that another three times.

Touch-ups, final routing, and such:

First you will want to cut off any really bent/damaged wire ends (do not lose those wire designators). With wire this fine they can easily break over time, and it would be saddening to have it stop working; I know, I had a model do that once. Using the hobby knife, scrap about 1 to 2 mm of coating off the end of the wires sticking out of the engine. You will see it become a very bright copper colour, instead of the red-orange of the polymer insulation typically used. Using a fine tip soldering iron, blob some solder onto the scrapped part. It will just tin it or blob a bit, that is all that is needed.

The following is not going to follow best soldering practises. That is fine, the joints will be more then strong enough for the project. The components being used are typically board mount only so improvisation is the key. You will want to do this on a surface that will not burn or will join with the solder. I had a piece of aluminum which I covered with Kapton tape because I had that laying around. A ceramic tile would be ideal, possibly a silicon mat. Holding the LED down with tweezers, carefully apply a blob of solder to both of the contacts. Do not go much above 660 degrees with your soldering iron. Next, tape down the wire, weight it, whatever, close to the end where you will solder the LED. Place the LED just touyching the tinned portion of the wire and hold it with tweezers. With a blob of solder on the tip of the iron, touch the two together, they should join. Do not take more then a second or two to do this. Repeat until you have two wires on each LED. See the image below for the ideal way to do this, you do not want anything sticking out the back. It will be much easier to glue the LED flat onto the engine.

You will have to make a note which side the anode (positive) and cathode (negative) of the LED are on which of your labeled wires. There is no universal marking method, you will have to check with the datasheet of the LEDs you chose and physically look at then. The jewelers loupe goes a long way here. If you don’t know what type of LED you have (and why do you not?) you can use a diode checker or a DC voltage checker to figure out the polarity of the LED. There are many guides to this on-line.

Now, pull the wires of the LED as a pair to bring the LED into the engine. Once into the engine, carefully pry the LED off to one side and put a tiny drop of super glue behind it on the center of the engine. I used the jewelers loupe and a pin to dab the glue in there. Then press the LED into the glue, make sure to hold it there a few seconds until the glue drys. Super glue is insulating (don’t ask how I know this), so there is no worries if it gets on things.

Repeat for the other LED.

Once all that business is complete, patch all the tiny holes with epoxy putty. Tip, gather the wires coming out the bottom of the A-wing and try to keep them bundled. This makes getting them through the stand easier and less likely to bunch up and jam. Let the epoxy dry before going any further.

Touch up all the paint and drill spots as required.

I slipped all the wires through the stand then glued it all together. The reason is I wanted to avoid getting the wires caught between pipes of the stand and such. I would pull the wire fairly taut and half put the stand pipes together. I would apply a tiny drop of super glue and quickly squeeze them together. The stand pieces are likely acrylic and most super glues will weld acrylic. Once it is together, that is it. Eventually I got all the stand pieces together and then glued the model to the top. After I inserted the pipe into the stand base; even though the center peg is cut off the base there is the two side pieces that will wedge the pipe in place.

Pull the wires forward or backward, into that channel melted into the base earlier, and glue or epoxy the battery holder over the opening. For the last of the wiring I connected the cathodes (negative side) of the LED’s to their own separate resistors. The reason is while you can have two LED’s connected to one resistor, they are not a perfect match and one tends to glow brighter then the other. Sometimes it is not noticeable as the tolerances get ever better in commodity components. The other possibility is because of the difference one will be handling more current and depending on a number of things may burn out before the other. The way I did mine, not likely, but it could happen. After all that work, why risk it? Those resistors are then soldered to the negative of the battery holder and the anodes (positive side) of the LED’s to the positive of the battery holder. If you want to get fancy, it is possible to get very small toggle/dip switches that could handle a few milliamps DC. They can be a bit challenging to source. It is harder to switch DC then AC currents, but that is beyond this article’s scope. Then you could turn the model on and off without having to remove the battery every time.

That is it.

 

A thing about current, the wire used, and deciding values:

36 AWG wire is tiny. The amount of current it can handle is very limited, you could get around this by using more wires in parallel but wire is not a perfect conductor. They have resistance, this leads to unbalanced current load in each wire which can lead to a burn out, like a fuse (which is essentially what is a fuse). When that happens the load on the other wire that burnt out gets split across the remaining wires, which causes more of the wires to burn out, repeat. A cascading failure is the result. You could go to a slight larger size like 35 AWG of 34 AWG if you need really bright LED’s. Going too big makes it hard to route the wires, it is best to work with something as small as you can deal with and work within those limits. The AWG number gets smaller as the wire get physically bigger (so #2 is much larger then #14). Lucky for us we do not need much current. I ran the LED’s at about 3 mA (milliamps) each. The wire is rated to carry approximately 35 mA in enclosed spaces/bundles where cooling is limited. It can carry up to 210 mA (a fifth of an amp!) if it is in the air/cooled and not enclosed. I do not recommend doing that, it will get hot. The LED’s I used could go to about 20 to 30 mA but they are painfully bright at that point. I do enjoy whatever eyesight I have left.

So how do we pick our resistors then? We will need to know how much current we need, the voltage of our battery, and the voltage forward drop of the LED. The last bit means you need to have a certain amount of voltage or more, otherwise the LED will not conduct, therefore not be lit. This is typically 1.5 VDC to 1.7 VDC (Volts Direct Current), you can measure to be exact but that is not at all required. I just went with the datasheet rating of 1.5 Vf (Forward Voltage). So I need at least 1.5 VDC to light.

Cool, now what? Well I choose the CR2032 battery because it is flat (good fit under the base) and 3 volts which is more then I need. It’s mAH rating is also descent (mAH is milliamp-hour which determines how long it will last with a given current draw). Voltage does not magically disappear. I can not use just 1.5 volts of the 3 Volts; in a circuit, the potential (voltage) must return to zero at the end of the circuit/path. So what do we do? We need a resistor in series with the LED to drop that extra voltage, the nature of the LED is it will always drop its rated voltage, for me that is 1.5 VDC. So we will always have 1.5V across the resistor as a result. If I used a 9V battery the LED still drops 1.5 VDC but the resistor is now dropping 7.5 VDC.

Almost there! The other thing about LED’s (diodes in general) is when they conduct they are a short. This means they will draw all the current they can from their source. Usually releasing the oft-joked “magic smoke” or “blue smoke”. “Magic smoke” powers everything, once the smoke is out, you can not get it back in and it will not work. In other words, they will burn. So we need to limit the current, and that is the other purpose of the resistor. The voltage across the resistor is fixed (our battery minus the forward voltage of the LED), so by varying the resistance we vary the current. Ratios! So there is some math, if you are really bad with math thenuse one of the many interactive online ohms law calculators where you can enter two values to get the third.

Ohm’s Law is Voltage (E) = Current (I) * (multiplied) Resistance (R)
Or E = I * R

Keep your bases the same at all times! If you used say milliamps, you must use milliohms or millivolts, and your answer is in millis! Very important!

Well we know our voltage and what current we want. So with some magic rearranging R = E / I
With numbers R = 1.5 / 0.003 (0.003 is 3 mA written as amps)
R = 500 ohms.

I want a 500 Ohm resistor. But (of course, something else, I mean, what else did you expect at this point?) what about power? The resistor has to be able to handle the power going through it. Electrical power (in Watts) is easy.
Power (P) = Voltage (E) * Current (I)
or P = E * I
With numbers P = 1.5 * 0.003

P = 0.0045 W
Power is 4.5 mW (milliwatts)
Well the resistors I used handle a quarter Watt or 250 mW. I think we’re safe here.

A lot of SMD/SMT resistors are in the 1/4 to 1/8 Watt range, more then adequate for our purposes. But always check if you are unsure! It sucks to come so far and have something burn or melt with no way to fix it.

 

Conclusion:

You now have a lit A-Wing!

It will bring all the nerds to your yard!

And they’re like, it’s better than yours!

Damn right it’s better than yours!

I can teach you, but I have to charge.

ANYWAYS. I hope this guide provided you with some insight into how I made my choices regarding this mod, and that it gives you enough information to do it yourself!

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