With Halloween coming up quick, we decided to make a spooky prank you can play on a friend. This spider will drop down from it's ledge when someone walks under it.

This is a simple project using a PIR motion sensor and a servo that can be completed in just a few hours. Try it out and see who you can spook!

Step 1: Parts List

1 x Geekduino

1 x Duino Mount Kit

1 x Sensor Shield

1 x Small Workbench

1 x Motion Sensor

1 x Sensor Cable

1 x 9g servo

1 x Experimenter's Nut and Bolt Pack

1 x 3D Printed Spider

1 x 3D Printed Servo Stand

1 x 3D Printed Horn Attachment

4 x Pipe Cleaners

1 x 6V DC Power Supply

1 x Gear Tie

1 x Fishing Line or String

Step 2: Designing the Spider

For the spider body we used the spider from our spider jump tutorial and modified it to make it smaller, remove the spring holder, and add a hole at the end for a fishing line attachment. We added the hole at the end so the spider would drop head first making it look more realistic.

Step 3: Wiring

As you can see, the wiring is very simple. The servo attaches to pin 11 while the PIR sensor attaches to digital pin 12. We taped a small tube around the PIR sensor to limit the sensing range. This is not required, but does make it so the spider will drop only when you are next to it.

Step 4: Assembly

Cut eight legs from the pipe cleaners and place them in the holes in the spider body. We used glue to secure the legs so they would stay secure during the drop. Cut a length of fishing line and tie it to the end of the spider. Tie the other end of the line securely around the servo horn attachment. Repeat this step with a shorter length of fishing line, tying one end to the spider and making a loop at the other end. Place your gear tie around the servo and twist the ends to secure.

Step 5: Code

Spider_Wiggle.ino
Download

Step 6: Optional - Designing the Ledge

This project can be modified to use a ledge to hold the spider before tipping it off. We made two ways to do this. The first way is a simple 3D printed part that attaches to the servo horn. A piece of cardboard or other material can be placed in this horn attachment and your spider or any other object can sit on top.

The second way is a 3D printed web that the spider sits on. We modified this web to attach to the servo horn.

Using either of these options, you would not need to tie any string to the spider.