In this Intstuctable I’m going to show you how to make a very simple motion activated spider that drops down rapidly and startles anyone that walks underneath, then retracts. I designed this to be an inexpensive and practical electronics project that a beginner can make. The sensor directly powers a transistor that runs a motor to reel down a spider. The reel is attached to a rubber band, when the sensor pulse ends, the motor turns off and the rubber band winds it back up. The speed of the spider drop can be adjusted by simply winding the rubber band more or less, from a slow realistic decent to a startling plummet.

It can be built using only a handful of inexpensive electronic components, some plastic bottle caps, cardboard, a rubber band and a motor. If you have to buy every single part it will be around $20, much less if you have some basics. No microcontroller or programming is required. It works very reliably and best of all, it actually does scare people!

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.

Electronic parts:
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

Motor 3.49
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.

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

Some wire
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:

Craft Supplies:
Plastic spider
A pin
Long Rubber Band (as sold to hold file folders shut)
Cardboard, about 2 square feet of it.
Hot Glue
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
Zip tie
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
Soldering Iron
Black permanent marker
wire strippers

Very clever approach!. What happens if someone stays close enough that the PIR stays triggered? Would the motor wind up the rubber band until it broke?
No, the spider actually stops when the string unwinds all the way, the rubber band balances it out so that it is strong enough to turn with the help from the weight of the spider but not after it reaches the bottom where the weight works against it. In the opposite direction it is stopped by the spider hitting the hole the string goes through. In short, if you stay under it, the spider just stays down.
<p>how does the motor not burn out then if someone just stands under the sensor for a long time? As you said, the motor isn't strong enough to pull the spider up, so won't it just draw more and more current which will eventually ruin the motor?</p>
<p>The main reason it is ok is that this PIR gives you a high pulse for <br>about 2 seconds, then turns off for about 3 seconds, so if you stand <br>under it and keep moving around it will just drop and retract over and <br>over. It also helps that in this case I'm using it at very low power so <br>stalling doesn't really cause it to heat up much. If it were a big <br>powerful motor moving a large prop I suppose I would have set up a <br>switch on the reel such that it would turn off when it hit the bottom, <br>and turn back on when it finishes retracting so that <br>the motor would always stop at the end of travel.</p>
<p>Thanks for the quick response! I have another question: how do you recommend that someone find an appropriate motor for this project? I already built the whole thing, but unfortunately, the motor I used is WAY too strong and the rubber band has no effect on it since the magnets are strong and it takes significant force to turn the armature. It doesn&rsquo;t stop at the bottom like it is supposed to, the motor just keeps going, reeling the spider back up the wrong way. You said that the motor you used is from a floor sweeper, so you obviously don&rsquo;t have any specs on it, but is there a test that people can do to see if a motor is too strong or weak without having to construct and glue on a new reel each time they try a new motor? I was thinking about trying this motor: https://www.radioshack.com/products/radioshack-6vdc-micro-super-high-speed-motor?variant=5717359749</p>
Clever and elegant - Well done!
Very nice! Congratulation <br> <br>:-)
Thanks for the great project! <br> <br>I picked up my PiR sensor from a different source, and found it only outputs under 2V when active, therefore not enough to get the TIP41C to be fully on to drive my motor. In case anyone else finds the same, an additional transistor (I used a 2N2904) between the PiR output pin and the limiting resistor for the TIP41C sorted this. <br> <br>Now we're back on track for Halloween 2012!
Thanks for the details on your variation.
Hi Paul <br> <br>I'm having difficulty matching the motor and rubber band - hoping you found same and have some advice here. The first motor I tried was a small high rpm hobby type and it wasn't powerful enough in the end to wind the spider down against the force of the rubber band. <br> <br>I've now re-assembled it with a DC motor scavenged from a printer and I'm having the opposite - the motor is strong enough to wind the spider down, then keep winding until it comes back up again. Even when I've pre-wound the rubber band some, the motor always wins. <br> <br>I'm thinking of putting a potentiometer in the circuit to limit the voltage to the motor, but with time against me hoping you have some advice that can help. <br> <br>Thanks ! Geoff
What are the pins for and the paper towel tube for? Also this motor has changed radio shacks motor is has a short shaft and the gear is on the very end. Any idea where I can find a motor with a longer shaft like the one you used? Im still having trouble finding a box for this.
The paper towel tube is to narrow down the field of vision of the PIR so it doesn't go off unless someone moves directly beneath it. <br> <br>That motor is from a floor sweeper that I took apart. Many printers and other devices you could take apart would have a motor this size, so many would work that I can't really recommend a specific one to buy.
cool <br>
Hey there, nice project! <br>I'm trying to do something somewhat similar (triggering a dc motor with a pir sensor), and your circuit layout works to trigger the motor, but the motor seems to be triggered even without any motion to the sensor. So basically, the motor turns on for 6 seconds and then off for 6 seconds, constantly. <br>I can't figure out what I'm doing wrong. <br>Any suggestions?
I don't know the specifics but there are a few possibilities. It has a warm up time during which it calibrates to the normal state of what it can see, before that it isn't very reliable. I think its about 30 seconds. If the thing you are activating makes the part that the motion sensor is attached to move, it could be shaking it's field of vision making it detect motion, I ran into this issue when the sensor was in a free hanging pail. It could just be that the field of view is too wide, it sees about 180 degrees all around, so you could try putting cardboard blinders on it to limit the field to the region you want to detect in. Last and least likely, if it is looking at a scene that has stuff that doesn't move, but does rapidly change temperature, or that reflects an area that has moving warm objects or changing heat patterns it would see that as motion.
Thanks for your reply. <br>Well, I've tried a couple of different things, and unfortunately nothing seems to solve the problem. I even hooked up a spdt relay (with a transistor) to see if that would help. Works perfectly with an LED in place of the motor, but when connected to the motor the relay just keeps triggering every 6 seconds, it's very odd. <br>Maybe some sort of kickback of power from the motor? I know next to nothing about electronics so troubleshooting takes a lot of time and research for me to try to understand what's going on with the circuit. <br>I'm hoping to use this circuit for an art project, which I'm displaying in a week and a half so I'm freaking out wondering if I can get it to work. Maybe back to the drawing board for me.
I think you can get it working in that time, Are you sure the motor jiggling the sensor isn't the problem? Because that's exactly the problem I had when it was having the trouble you describe. If you think it may be electrical try putting the motor and transistor on one power supply and the sensor on another with only the grounds tied together. If that fixes it then it is electrical and you need a bit more isolation.
Hmmm... no I haven't tried that, but it sounds promising! I'll let you know how it turns out.<br>Thanks again.
Cool idea! Maybe you could place the sensor forward some so it triggers before someone is under (or past) it.
That would work well. You can aim the trigger area by pointing the tube too. Then you could do something like fake saws that spin when the person gets within a certain distance from the front. Of course saws or other props that just spin wouldn't require the whole rewinding mechanism.
Nice idea. Adding a guillotine blade (not real) instead of spider could be more scary, I think.
I hadn't thought of that, but that would work, you could even fit it in a sliding frame if you wanted. It could work with pretty much any prop, bats and snakes or a fake hand would work too.
it would be great to add more reels in order to span across the whole top of the doorway so that a herd of spiders dropping down at once instead of just one.
I was thinking of something like this. One sensor could actually be attached to as many of these as you like. You could even make a haunted house room where when someone gets to the middle spiders lower down all around them.
nice, but it could be a tad stealthier.
It can also be mounted above the door out of sight. I showed it in plain sight for instructional purposes. But to demonstrate it in a stealthier mode I've added some pictures and video. Thanks for the helpful feedback.
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About This Instructable




Bio: I am a robotic engineer, and I like to make things and teach others.
More by PaulMakesThings:Add Radio to a Syma S107 IR Helicopter (or any other IR device) A 3D Print Ready Jack O' Lantern in Solidworks 3D Printed Hanging Internal Gear Clock 
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