Intro: Motion Activated Dropping Spider, Low Cost, No Programming
Step 1: Parts and Tools Needed
Note to people who like to scrap stuff:
If you find an old printer you can take apart, you can probably get the motor, the wire, a 3 pin connector, and possible the transistor and the diode for really cheap.
I used Radioshack and a site called www.taydaelectronics.com. Radioshack because it had the parts and Tayda because it lets you order in quantities of 1 and the shipping is low. Substitutions are very possible. Any transistor with enough continuous current capacity for the motor should work, in this case 800ma. I encourage scrounging a motor if you’re up for taking stuff apart, they’re in everything. If you're in a hurry to make this before Halloween all of this stuff can be purchased at a radio shack store.
Parallax PIR sensor Module $9.99
1-3/4” Mini perfboard (Comes in pairs) 1.99
If you scrounge a motor, try to get one like this with a gear, it will give the spool and the glue that holds it something to grip on to.
4 “AA” Battery Case
Any case that is in series to provide 6v will work, I like this one because it has a switch already installed on it.
TIP41C POWER TRANSISTOR NPN 100V 6A
If you need to buy this at the store, radioshack stocks the TIP31 and TIP120 either of which would also work.
120 Ohm resistor
1 1N4004 1A 400V Diode
If you don’t have some you can strip it out of an old phone cable, use some speaker wire. If you need to buy some there’s a link below, 2ft each of green, red and black 22awg stranded wire should do it.
If you’re uncomfortable soldering you can use this IC socket for the transistor, cut it down the middle with some clippers and you have two transistor sockets for 2 cents:
Long Rubber Band (as sold to hold file folders shut)
Cardboard, about 2 square feet of it.
Paper Glue or Wood Glue
A Paper clip
A milk cap
A 3" to 4" plastic jar lid wide enough to make the drum of the spool
Thread or fishing line
Paper Towel tube or TP tube
Pin or tack
Pumpkin Pail (Only needed if you want to hang it from the ceiling, not needed for hidden over door mount)
Hobby Knife (such as Xacto)
Hot Glue Gun
Black permanent marker
Step 2: Build the Circuit
This circuit has only 3 parts.
The transistor works as a switch, letting current flow from the negative terminal of the motor into the collector (labeled C) and out of the emitter (labeled E) When it gets a positive signal from the PIR at the base (labled B). Keep in mind when you follow this diagram that if you use a substitute transistor these pins may be in a different order. Though usually they are as shown.
The diode keeps the motor from shocking the system with back EMF (a pulse of high voltage that can occur when a motor turns off due to the spinning magnets passing the coils). Since the motor is small and the PIR has protection, you could leave this off, but I prefer to keep it safe.
The resistor is to limit the current from the signal wire in the PIR to the transistor. If you leave it out it will still work, it's just another protection feature.
Now, to make the circuit. My preferred method for items that are too simple to fabricate a PCB, like this one, is point to point soldering on a perf board. Each of the components is put through the breadboard, the leads are bent to hold it, then the extra is clipped off. The body of the component should be on the plain side and the leads should stick out of the plated hole side. Solder each component to the breadboard then solder bridge the points that need to be connected by adding some solder and dragging it with the iron until the points merge.
A layout is shown below that allows this circuit to be made with no jumper wires. The white indicates solder bridges. The red and black wires are not stuck down to the board, the ends are just soldered in.
The negative and positive wires on the diagram, and the motor need to be the ones that make the reel lower the spider when connected to the battery pack negative and positive.
To make the wire connector for the PIR use the piece of a socket, or another 3 pin female header and solder it on to the end of the three wires. You could solder the wires directly on to the PIR but I didn't want to fix it to this permanently, and that would make it harder to work with for the install.
Step 3: Build the Reel Mechanism
My first build used a metal jar lid, instead use a plastic lid about 1/2" thick and 3" diameter. Its easier to cut, more rigid and hot glue sticks to it better.
Take the milk cap and poke a hole in the center, it doesn't need to be extremely exact. cut two slots for the rubber band about 1/4" from the center on either side. (first picture) Cut the rubber band in one place and feed an end through each slot in the cap. Tie a knot in each end to hold it on. Double it over and
Use a 1/16 drill bit to put a hole in the center of the plastic jar lid if you're using a motor with no gear, otherwise use whatever diameter makes it fit past the gear. Put two holes close together on the side of the drum wall of the plastic lid between where the two flanges will go. These will be used to attach the string later and putting them in the center of the wall makes it less likely to jump off the spool.
Take a piece of scrap cardboard and cut a tiny slot with your hobby knife, just wide enough to fit over the motor shaft and deep enough that the spacer covers the motor. Place the spacer on the motor shaft. This will allow you to press the parts of the reel down to level them without jamming it against the motor.
Push the plastic jar lid onto the motor shaft, topside against the motor open side away from it, until it is up against the spacer. Keeping it pressed against the motor, apply a small amount of glue. Check that it's fairly steady when spun before gluing it all around, a little wobble is ok, this isn't going to go very fast. Once it's straight enough glue around the motor shaft where it meets the lid.
Now take the milk cap with the rubber band in it, apply hot glue to the remaining part of the motor shaft and press it down on to the shaft. If you're more patient use epoxy or gorilla glue for this part.
Glue around the edges of the milk cap against the jar lid. You can take out a little more of the wobble if you have any here by holding it straight when you glue this.
Now pull out the spacer and check the spin!
Step 4: Finish the Reel Body
To make sides for the reel take some more cardboard from a cereal box and mark out two doughnut shapes with a compass. The inner diameter should be at least 1/2" inside the jar lid which was a 2" diameter in my case, and the outside diameter should be about 3/8" outside of it, which gave me a 3-1/2" diameter.
Before cutting out the middle mark a circle the same size as your lid to help you center the part when you attach it.
Cut the cardboard, make sure that the outer edges are very smooth so the string doesn't catch on them.
Center each side using the marks and glue it on.
Step 5: Build the Enclosure
I used cardboard for the enclosure so that this would be easy for anyone to repeat at home, but wood or plastic would work very well if you have the tools to work with them. The inside dimensions are 4”x6”x2.5”. I left the top mostly open. It should be just wide enough to clear the spool, which as constructed here is 3.5” in diameter. As you can see from the picture I’ve used an existing box that wasn’t quite wide enough and I needed to cut out the sides to make the spool clear.
The top part should be built so it can fold up to access the motor compartment.
Before you close it up, cut a hole the size of a quarter in the bottom of the box, about 1.5" behind the reel. This is to mount the PIR sensor later.
Step 6: Mount the Motor to the Enclosure
Cut 2 pieces of wire 12" in length, strip about 1/2" off each end, loop them through the motor tabs and solder them on.
The motor will need to be positioned so that the rubber band is taken up but not stretched when pulled to the opposite edge. Once you find that point mark it out and put some small holes in the cardboard for zip ties to go through.
Zip tie the motor into place, then put the paper clip over the rubber band and clip it to the other side of the enclosure. Check that the spool spins freely, if it doesn't, adjust it or cut away part of the box. Once the placement is good secure it with some hot glue where the motor meets the cardboard.
cut a small hole in the back top corner of the enclosure and feed the motor wires through.
Step 7: Rig Up the Spider
Poke a hole in the enclosure centered under the spool, the centering between the walls of the spool is crucial, if you put it off the side the string may hop the spool when it retracts.
Feed the thread through the hole you just made, then into the hole in the spool and out the other. Tie it tightly against the drum.
Loop the other end of the thread around the pin or tack and tie it securely, then slide the knot up under the head. Press the pin into the plastic spider at the rear tip of the abdomen. The system will work with the string attached anywhere, but this is the location of the spinnerets on an actual spider.
Now you and take off the paper clip, and wind it up until the spool draws the spider all the way up. Then give it a few more twists. Now to test it, touch the wires to the battery pack. If it tries to pull the spider up you need to switch the wires to the opposite contacts. If it doesn't lower enough, unwind the rubber band a bit, if it doesn't retrieve, wind it up more.
Step 8: Install the Electronics
Use small screws through the cardboard or tape to stick the circuit board to the side of the enclosure just so it won't be loose.
Use hot glue to stick the PIR into the hole in the enclosure facing down. Feed the wire to the PIR through the same hole that the motor wires come out of and plug it into the PIR.
If you want it to go off whenever anyone is near, leave it as is. If you want it to go off only when someone walks directly underneath it, you will need to give it some tunnel vision by cutting a 1" piece off the cardboard tube and gluing it on around the PIR sensor.
Attach the battery pack to either the side or top of the housing. Make sure the switch is toward the top if you put it on the side.
At this point if you clip the rubber band to the edge, wind it up till it retracts the spider, and turn it on, it should work. It will just go off repeatedly since you're holding it.
Step 9: Install the Reel in the Housing
To mount it hanging from the ceiling in an enclosure first cut a hole in the bottom of the pumpkin pail with your hobby knife, make it big in the middle for the spider to go through with an extension at the side where you want the tube for the sensor to come through. Carefully turn the mechanism sideways and set it into place inside the pumpkin pail.
To mount it above a door simply set the bottom edge of the box on top of a door frame and secure it all in place with a thumb tack.
Step 10: Done
-Install it in a fake hanging plant instead of a pumpkin pail to make the spider even more unexpected
-Replace the motor in this circuit with a relay to power a much bigger motor, wind a couple of bungee cables and drop a prop the size of a basket ball.
-Use the simple motor control circuit for other props, like a rattle snake that shakes it's tail when people walk by.
This is one of my first Instructables, so if anything is unclear let me know and I will update it.
Hope you have fun with this little piece of Halloween tech! If anyone builds this I would love to see pictures, especially if you make a version with a wooden enclosure or another variation.
Fourth Prize in the