Fitting LEDs to a 1/144 Jaguar GR.1 model


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Jaguar GR.1 birds eye view (38.1kB) This tiny model (fuselage length 11cm, wing span 6cm) was fitted with flashing wing tip lights and two oscillating fuselage anti collision beacons. Actually there should also be a light in the tail fin but I saw no way to fit either a LED or fiber optics in the fin.

There are a number of problems to solve when fitting electronics to a small model kit: room inside the model is limited, an oscillator circuit or batteries will not fit, so power and signals should be supplied from the outside. Ideally power and signals should be supplied by two wires so each wire can be run along a landing gear leg.

By using a NE555 timer circuit as a base for the oscillator circuit the problems can be solved: the output connection of a NE555 can supply as well as drain current.

Some basic info on using LEDs can be found on a separate page.

The electronics for this model consist of two parts: an oscillator circuit with power supply fitted into a display base and a small circuit with four LEDs, some resistors and a capacitor fitted inside the model. To light the wing tip lights, fiber optics were routed through the wings.


External oscillator circuit

schematic of NE555-based oscillator circuit (5.7kB) The NE555 timer circuit can be powered by voltages ranging from 4.75V to 15V and can be configured to generate a symmetrical block-shaped wave by choosing a much lower value for resistor R1 than for R2.
For the Jaguar I aimed for a 0.5Hz wave so I picked 22 kΩ for R1 and 1.5 MΩ for R2 with a value of 1µF for capacitor C1. For C1 I used an electrolytic capacitor, note polarity.

NE555 pins
pinfunction
1Ground (V-)
2Trigger
3Output
4Reset
5Control Voltage
6Threshold
7Discharge
8Power (V+)

Since I used batteries (four 1.5v AA-batteries) , I split the power supply into two halves. By connecting the LED circuit to this split, the output wave appears to alternate between +3V and -3V instead of +6V and 0V.


Electronics inside the Jaguar

schematic of LEDs inside Jaguar model (1.9kB)

The oscillator circuit provides a block-shaped wave with equal 1 second periods of +3V and -3V. The lighting consists of two pair of lights: one pair of red alternating lights on the back and belly of the fuselage and a light for each wing tip (red for left, green for right).
By reversing one in each pair of LEDs one will light at the positive part of the wave whilst the other lights at the negative part.

The wing tip lights flash then light up normally, this is done by adding a capacitor in series with the wing tip LEDs.
Since a fairy large capacity is needed in a small package, a bipolar tantalum capacitor (10µF, 6V) was used. Be sure to pick a bipolar type as tantalum capacitors may explode when submitted to voltages outside of its range. Apart from a small size another benefit of tantalum capacitors over electrolytic capacitors is that these can not leak.
Components used for the Jaguar (20.4kB) The LEDs used require less than 10mA of current so a value of 120 Ω was used for both resistors in the schematic.

The actual components were selected for minimal size: micro-mniature LEDs with a lens diameter of 1mm, small 1/8W resistors and a small tantalum capacitor. Due to its weight and size the capacitor was placed well forward in the fuselage, right behind the engine intakes.
The whole circuit was assembled by connecting the leads of the components and some solid core low voltage wire, then all connections were soldered. With the LEDs for the tip lights care was taken to make sure the LEDs could be repositioned by bending the leads, this was done by bending the leads of these LEDs in gentle curves rather than making sharp bends.


Assembly

All of the electronic components (four micro-miniature LEDs, two resistors and a capacitor) were fitted inside the center fuselage, forward of the main landing gear.
The LEDs for the fuselage anti-collision beacons were fitted to the fuselage by drilling a hole the size of the lens of the LED at the proper locations, inserting the lens of each LED through the hole and fixing the LED in place with some CA glue.
To light the wing tip lights, a small bundle of glass fibers was inserted into a length of shrinkable tubing of 1.5mm diameter and cut to a length of 35mm, then a groove was carefully cut across the underside of the wing, running from the wing tip light to the wing root in front of the mounting tab.
The fiber bundle was placed into the groove and secured with a few drops of CA glue applied to the shrinkable tubing. After the CA glue had cured a loose LED was used to verify that the fiber bundle conducted sufficient light, then the groove was filled using model putty.
After the putty had cured and was sanded flush, wing pylons were fitted to reinforce the wing.
The tip light had been cut away before, its rough shape was formed by the ends of the glass fibers, some CA glue was used to recreate the smooth shape of the tip light, this was later carefully sanded into the exact shape.
A 1.7mm hole was drilled in the fuselage side of the wing root at the location where the fiber bundle emerged from the wing, making sure the fiber bundle would slip through the hole unobstructed when the wing mounting tab was inserted into the fuselage.
This procedure was repeated for the other wing, whilst making sure the location where the fiber bundles emerged from the wings differed by at least the width of a LED body.

Then the LEDs for the tip lights were carefully aligned inside the fuselage so that the maximum amount of light reached each wing tip light.

Jaguar GR.1 frontal view (15.0kB) Finally a hole was drilled in each main wheel bay just inside of the main landing gear leg and each solid core connecting wire was fed through one of the holes. The insulating sleeve was stripped off of these wires and the wires were made to look like the stabilizer bars of the landing gear, with the ends of the wires running between the main wheels and touching the ground.

The oscillator circuit and batteries were fitted to a base, a pair of small metal tabs mounted flush with the surface of the base supply the output from the oscillator circuit to the Jaguar.
Since the output wave is symmetrical, the model can be placed over the metal tabs facing either way.




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