Flickering Torch Prop

I wanted to make a prop torch for part of a costume that would be fairly robust, re-usable (i.e. not a one shot prop) but also be fairly safe. Since I wanted to make it look like fire, I made it flicker with an Arduino sketch and a LED array.

Step 1: Gather Materials

Here is the list of materials I used for all of the project. Substitutes can be made depending on what you have available in your area. This is what I had and used, some of it for convenience rather than accuracy.

• 600mm x 240mm x 1mm cardboard (Ridges of the cardboard along the length, not across the width)
• 60mm x 75mm x 3mm perspex
• 580mm x 12mm dowel rod
• Macetech MegaBrite LED array (Documentation)
• Arduino Nano (version 3.0)
• USB battery pack (Like this one but any similar sized one would work)
• USB (Type-A) to mini USB (Mini type-B) cable
• Female to female jumper cables
• A cheap cotton pillowcase
• Yellow poster paint
• Dark oak wood stain
• about 600mm copper wire
• Scrap cardboard
• Rubber bands
• String

Tools and other things used include:

• Hot glue gun (and lots of hot glue)
• Pliers
• Wire cutters
• Paint brushes
• Sandpaper
• Kitchen roll
• Masking tape
• Blu-tak (to hold things in place)
• Solder + Soldering iron

Step 2: Making the Body

Using the 600mm x 240mm x 1mm piece of cardboard, bend it along the grain of the cardboard to be able to roll it into a tube. I didn't pay too much attention to accuracy and this gave it a more organic look.

I used a piece of kitchen roll and a large paint brush to liberally apply two coats of the Dark oak wood stain to the cardboard tube. Again, I wasn't too bothered about an even spread because it is meant to look like a tree branch. The tube was then left to dry.

I used hot glue along the length of the cardboard to make it into a tube. The diameter of the tube isn't too important but I made it to resemble a fairly chunky branch and so it could hold the electronics inside itself.

Step 3: Making the Flame

I didn't want an actual flame (not very safe) so I made the shape of a flame and used LEDs to illuminate the shape from below.

To frost the plastic, you can either buy it frosted or frost it yourself. I went for the second option by using sandpaper on a clear piece. I would recommend using 80 grit (or more coarse) sandpaper since higher grits make a smoother and clearer finish. The difference can be seen in the comparison picture.

To make the shape of the flame, I used two pieces of copper wire (about 300mm each), bent them into an angle and then soldered the ends together. You might need to use a high powered soldering iron or propane torch to actually melt the solder to make the two pieces stick together. Or you could use hot glue or epoxy resin or some other glue.

Because the wire needed to be attach to the frosted plastic and it wasn't laying very flat, I used a fair amount of hot glue to attach one to the other. After securing it well, I twisted the wire a little to make the form into a bit of a spiral.

I used yellow poster paint mixed with a fair bit of water (probably about 1 part paint to 5 parts water) to make a yellow paint bath. I cut a corner from a cheap pillowcase and submerged it in the yellow paint bath. I agitated the cloth in the paint so that the cloth was evenly coloured. You don't want to make the bath too thick here: you're trying to change the colour of the fabric but keep it translucent. You can see a colour comparison in the picture.

The form was then put inside the dry cloth to ensure that there was a fairly large overlap of the material.

Step 4: The Electronics Bit

This bit makes the flame flicker. It isn't necessary but it makes the torch look more authentic to me.

Using the dowel rod and the scrap cardboard, I wrapped some of the cardboard (in 50mm wide strips) around the dowel. After getting a few layers glue on, I attached some loops of string so that I could extract the electronics when I wanted to. I then added enough more layers of cardboard to make this bit a snug fit within the cardboard tube. (i.e. The outer diameter of this part is just less than the inner diameter of the tube made earlier.) The amount of layers you'll need will depend on the size of your tube and the thickness of your cardboard shims. Keep going until it's snug and hot glue down each extra strip. I put on another spacer using 30mm wide strips near the LED array to limit the movement of the electronics.

The electronics part is wired up quite simply:
LED array <- female to female hookup wires <- Arduino Nano <- USB cable <- battery
The sketch I used is included here with comments in the code. It should be fairly self explanatory. The Arduino Nano randomly changes the red LED between an upper and lower value and matches the green value to half the brightness of the red LED and adds a little bit of jitter until the battery connection is removed. You could just vary the brightness on some yellow LEDs using an Arduino nano. I wanted it to be fairly bright and didn't have any suitable orange or yellow LEDs to hand so use the MegaBrite instead.

I then attached the electronics to the wooden dowel with some masking tape and used a piece of Blu-Tak to attach the LED array to the very end of the dowel. The length of the dowel was such that the LEDs would be near to the frosted plastic without touching it. All the components were allowed a little slack but not so much that they flopped around inside the tube.

Step 5: Putting It All Together

I used hot glue to attach the frosted plastic + form to the top of the "wooden" tube.

Then, I used the coloured pillowcase corner to cover the flame form. A rubber band was used to hold the cloth in place and allow a bit of shaping. Another rubber band was added to cover this up and make extra flame shapes.

The electronics were then partially insert into the tube. The battery was connected to the Arduino Nano via the USB cable and then the electronics section was fully inserted into the tube.

I think that the battery could keep the electronics working for 10+ hours so it should work fine for an evening out.

Step 6: Improvements

Overall, I am happy with the result and I suspect I'll use it several more times without much modification.

Some improvements that could be made include:

• Use more / different materials for the flame form to make it look more like a flame.
• Not use copper wire since it is rather stiff and could be construed as dangerous by some people, i.e. people who want to hit other people with props.
• Use hot glue instead of solder to soften the end of the flame.
• Use more layers of material to have different colours without so much dependency on the light.

There are probably other things too but I'm happy with how it turned out.