Animated Jack-O-Lantern




Introduction: Animated Jack-O-Lantern

About: Recently finished a Ph.D. in Mechanical Engineering. Still love creating in my spare time
This Instructable will show you how to animate a Jack-O-Lantern using Shape Memory Alloy

I decided to create this pumpkin because I find that jack-o-lanterns are too static, they just sit there staring. I wanted to create a pumpkin that not only looks great, but actually moves.

Step 1: Gather the Materials

To animate your pumpkin you will need:

- A Pumpkin of your choosing
- Aluminum channel bar
- Threaded Rod (8 NC 32)
- 1 8NC32 Thread Nut (Meccano Size)
- Bamboo Skewer
- Fishing line
- Small piece of Plexiglas
- Solid Core Wire
- Stranded Core Wire
- 3 Large Paper clips
- Candles (for the pumpkin)
- Appropriate pumpkin pattern to animate

And now for the more exotic material:
- Flexinol (a Shape memory alloy)

I got my Flexinol by ordering directly from Dynalloy (have a wide variety of choices), but it is also possible to get it from places like Jameco (more limited selection).
If you can't get Flexinol, it is possible to still animate the pumpkin using the same frame and setup, just attach a motor that will wind up the fishing line, where the Flexinol would pull it.

- Pencil
- Pliers
- Hack Saw
- Tin Snips
- Drill
- Drill Bits
- Tap and Die set (optional)
- Glue Gun
- Knife
- Pin

Step 2: Form the Frame

The first step is to build the frame that everything will be attached to.

To do this you will first need the measurements of your pumpkin; the maximum internal height and depth from front to back (you can just eyeball it). This will allow you to form it into the shape in the last picture of this step.

The first step is to create the overhang where the Flexinol will attach.
To do this, measure about 5 cm from one end of the aluminum channel bar and mark it on the side without the opening.

Next, draw 2 lines at 45 degrees from the back of the bar

Now cut along the lines using the tin snips (you could use a hack saw, but it would be very hard) and then cut the back side to match (See pictures).

Now simply bend it with your hands to a 90 degree angle.

Repeat these steps for each corner, being sure to measure along the back of the bar. This is so the extra material ends on the inside and it still fits in the pumpkin.

When you have made the last bend, cut off the extra material about 1 cm above where you want the middle of the moving pumpkin parts to be.

Step 3: Prepare the Frame

This is a simple step, Drill the holes where they are needed.

The size of drill bit I used is a 9/64" bit, the size recommended by my tap set for an 8NC32 thread.

The first set of holes is for the Flexinol, one on the overhang and one along the bottom channel along the vertical line with it, but more toward the top of the channel bar.

Now you need holes to guide the fishing wire to the front. The first hole is needed along the bottom bar, lower in the channel to avoid rubbing the Flexinol anchor and switch later. The last guide hole is needed in the lower front corner, on the bottom channel.

The Final hole for this step is the switch hole. It should be placed along the bottom bar somewhere in the middle away from the other holes. It should also be drilled near the top to avoid the fishing line.

All of the holes in this step should be tapped using a 8 NC 32 thread size. If you don't have a tap, you will need to get some nuts to fit your threaded rod, and use a slightly larger drill bit.

Step 4: Thread the Flexinol

To calculate the length of Flexinol, start by measuring the inside distance from bottom to top of the frame, and multiply it by 2.

Next, attach the crimps to the Flexinol by threading the Flexinol into the crimp hole and pinching it closed. To do this I used the space on a pair of pliers between the handles (See 2nd Picture), instead of buying a crimping tool. Do this on both ends.

Now to attach the Flexinol to the frame, cut a piece of threaded rod (metal to conduct electricity) slightly wider then the channel bar. Locate the lower Flexinol hole drilled and tapped earlier, and as you thread the rod into the lower hole slip one Flexinol crimp over to attach it.

Now take a bamboo skewer (electrically insulating) and push it into the upper threaded Flexinol hole and turn it. This is so it forms threads as it comes out the other side. Now cut the extra off each side so it is stuck in the hole.

Finally, Loop the other end of the Flexinol over the bamboo skewer and pull it down.
If the Flexinol is the right length, the loose end should not be able to touch the lower part of the frame.

Also, there is no need to worry about bending the Flexinol over the skewer. The skewer won't burn at 90 degrees Celsius (the temperature the Flexinol contracts at) and it won't hamper it contracting fully.

Step 5: Thread the Fishing Line

For this step, start by putting bamboo skewer into the fishing line guide holes drilled in the frame earlier, this causes them to become threaded. Then cut off the excess as in the last step.

Now cut a length of fishing line that can run the full length of the frame. Tie one end of the fishing line to the loose end of the Flexinol.

Now thread the fishing line under the bamboo skewers in the guide holes and up the front channel bar.

Step 6: Add the Switch

This is the component that will automatically contract and expand the Flexinol as needed.

The setup for the switch (it will be calibrated later) is pretty straight forward.
First, cut a piece of Plexiglas about 1 - 1.2cm wide by 2.5-3cm long.

Next, drill a 5/8 " (or slightly larger then 9/16") Hole in the middle of one end and 3, 1/16" holes in the other end.

Now thread a bamboo skewer into the switch hole drilled in step 3, and cut all of the extra off one side, but leave 1-1.5cm sticking out the other side.

Next, attach the piece of Plexiglas to the bamboo skewer by putting the skewer through the large hole and threading the nut behind the Plexiglas on the skewer. Tighten the nut down so the Plexiglas will move stiffly.

Step 7: Rough in the Switch Connections

To rough in the switch connections, you will need to first take a length of fishing line (15-20cm for plenty of working room) and tie it to the lower fishing line about 2-3cm behind and in front of the switch. Be sure to tie knots in both lines, so it doesn't slip later. Now bend the loose line tied to the lower line and thread it through the middle hole on the switch.

To rough in the electrical of the switch, take a length of solid core wire and strip it. If it is too thin, wind 2 pieces together as I did. Now thread each end of the wire in a side hole om the switch and wrap it around to fasten it tightly. Now bend it into a loop so it will contact the frame in front of the switch.

Finally, take a decent length of stranded wire and attach one end to the wire loop. Create a loop of stranded wire behind the switch, and hot glue the wire to the bamboo skewer in the switch hole (hot glue won't stick to the aluminum).

Don't worry about the exact positioning of the electrical wire now, it will be adjusted later.

Step 8: Prepare the Frame End

For this step you will need to start by drilling a hole through each side (9/64" Bit) of the front top of the Frame.

Next cut the bottom of the front channel out, about 2-3 cm from the top(See 3rd picture).

Now bend the sides outward and align the ends upward. This is so the Flexinol doesn't have to work as hard to lift the pumpkin.

Step 9: Attach an Anchor to the Fishing Line

The point of this step is to give the armature(see next step) something rigid to attach to.

To do this, take about a 3-6 cm length of bamboo skewer(it depends on the height of your front bar), and using 1/16" drill bit, drill 2 holes near the top (close together) and one near the bottom.

Tie the fishing line to the bottom through the hole you drilled, so the middle of the 2 holes are lined up with the holes on the top front of the frame (See pictures).

Step 10: Add the Animation Armature

For This step, take the paper clips and bend them as shown in the first and second picture.

Once You have made 2 of them, thread one in each side and attach them to the bamboo skewer by bending them around so they are loose (See 3rd picture).

Next, bend a 3rd paper clip around behind the other 2, holding them together (see pictures 6-7).

This configuration will create a flapping animation in the pumpkin. If you want to change the style of animation, here is where to do it.

Step 11: Calibrate the Switch

The first part of this step is to get a counter weight on the armature so it can function. Once you have that, pull the fishing line the same way the Flexinol would, to judge if the Flexinol has enough strength, based on the gauge you bought, to move the weight on the other end.

To calibrate the switch, tie the front fishing line to the plexiglas switch while the Flexinol is in a relax state.

Next, pull the Flexinol back to where it would be when contracted and tie the back fishing line attached to the switch tight to it.

The purpose of doing this is so that when the Flexinol pulls back, it will only turn off when it reaches the limit, and only turn back on when completely relaxed.


The switch does move!

Step 12: Pumpkin Carving

Now it is time to carve the pumpkin.

To start this step just follow the standard pumpkin mangling steps.

To attach the moving parts of the pattern to the frame, push it onto the paper clip spikes created earlier.

There are some photo notes on the pictures of this step to help you integrate the frame into the pumpkin better.

Step 13: Admire Your Masterpiece

Now all that is left is to set out the pumpkin on Halloween and enjoy the results.

If you do use this method, or a similar one, uploaded a picture and explanation of how it moves for the rest of us!

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    13 years ago on Introduction

    from where do you get the shape memory alloy?


    Reply 13 years ago on Introduction

    cancel that last request. I apologize, I skimmed the article the first time thru and have now read it and saw the link. Thanks


    Reply 13 years ago on Introduction

    Ah, well now it is easier for everyone to find :)


    Reply 13 years ago on Introduction

    I got my SMA (Flexinol specifically) by ordering directly from Dynalloy (ordered over the phone). But I have also seen it sold at Jameco robotics and various other online robotics stores.

    Hope it helps :)