R1 +9 V R2 RY Solenoid magnetic coil C1 + R1: 100K R2: 100K C1: 10 µF
Figure 3-2 Mechanical actuator timing circuit Figure 3-1 A small lever-type solenoid
value will make it a lot faster. Depending on the size of your fake furry critter, you may want a nice slow movement to simulate breathing, or a fast twitch to make it look as though the critter is shaking with fear, ready to invoke the fight or flight response.
If you need a little more response from the solenoid or motor you are using, there is no problem running the circuit up to 12 volts, but if your actuator is very low impedance, you may need to use a transistor driver circuit to source the needed current or your 555 may get hot in a hurry. Since there are only four components in the circuit, it can be built any way you like, even on a bit of cardboard by soldering the leads together after punching them through the board. I always keep a large stock of perforated board on hand, so the circuit has plenty of room for expansion on the 1.5-inch square board I have mounted it to (see Figure 3-3). Although not shown in the photo, I also added a small bit of felt to the top of the solenoid coil to stop the plate from slapping against the coil’s top so that it runs silently when the battery is installed. My system starts to run as soon as the battery is installed and has no on-off switch, but if you look ahead a bit, the next few projects have light-activated circuits that could
easily be adapted to this one so that it only runs when in a lit environment such as an opened closet or cupboard door.
Mounting the mechanics will depend on the means of activation and type of critter you plan to create, which could be as simple as the small bit of fur I used or something as complex as a wire-controlled puppet-like beastie. I wanted something small and simple that could be easily placed into a cupboard or dresser with minimal set up time, so I just put the parts into a box with an open top so that the actuator arm stuck out of the top as shown in Figure 3-4. This system could be placed practically anywhere then covered with a small 1 foot square bit of fur so that the mechanical parts are hidden from view
resulting an what looked like a large rat or weasel when viewed from the side. The actuator arm pumped the top of the body up and down so that it appeared the little beastie was breathing at a rate of about three times per second, giving the very
convincing illusion that it was actually alive. Most unsuspecting victims who encountered this mechanical critter weren’t brave enough to hang around and inspect the furry critter, or attempt to touch it.
If you do a little creative hacking, you could make a much more realistic breathing movement by creating a tubular critter with all of the
mechanics permanently mounted inside so that the actuator pulls directly on a strip glued to the
underside of the fur. A good place to start might be an actual small stuffed animal with the stuffing removed so that you can build a perfectly fitting actuator to place inside. The size of the critter is also limited only to your evil imagination, and if you find a large enough battery block, you could drive a very large actuator such as a windshield wiper motor to create a moving beastie as large as a gorilla if you really wanted to give your buddies a good scare.
Project 5—Alive and Breathing
Figure 3-3 Mechanical actuator circuit working
Nothing says “hello” better than a golf-ball-sized hairy spider right in your face after you switch on a light—yikes! Grab your soldering iron and a few components from your junk box, and let’s see how many of your normally “tough” friends will jump and screech like little girls when they are victim to this prank.
You could use a large plastic spider from the gag shop for this project, but the true Evil Genius is never satisfied with someone else’s work, so I made my own massive hairy tarantula look alike from a bolt and some black pipe cleaners from a craft store. Thanks to the bolt, this spider was able to swing with a bit of momentum, and when it smacked you in the chest, there was no question that this was a seriously huge insect. As shown in Figure 3-6, a small 1⁄
4-inch bolt and a few black
furry pipecleaners will be used to form the body and legs of the tarantula. You could also start with a ping-pong ball, or try something more elaborate
for a very realistic-looking spider, but that may not be necessary, since the mind will see a spider no matter how simple the prop may be once it starts to swing (as the lights are switched on), and by the time it hits the victim, he or she will probably already be shrieking with fear.
Pipecleaners are like long, thin, metal wires covered in hair-like strands, and can be found at most craft supply or dollar stores. To make the spider’s legs, wrap four of the pipe cleaners around