Automatic Halloween Spider Drop

The itsy bitsy spider climbed up the waterspout. Triggered was the distance sensor and washed the spider out.

This manual will help you to build your own motion-triggered Halloween spider, which will automatically be released and winched up again. A jump fall scare. It is able to handle really the large ones and people will love it (or not) if all of a sudden the spider legs touch them from above.

The mechanism is simple. A 180° servo tilts the 360° continuous servo to release a cord a spider is attached to, so that the spider falls towards the potential victim. The mechanism tilts back and the continuous servo winches the cord up again.

A 3D printer is helpful, but not necessarily needed.

software prerequisits

• Arduino IDE
• NewPing library
• PCA9685 library
• skull code

hardware

• ESP8266 or other development board
• HC-SR04 or HC-SR04P distance sensor
• PCA9685 PWM driver
• one 180° standard servo like MG 995/996
• one 360° continuous servo (example)
• power supply and jumper wires

other parts

• two servo brackets / mounts
• hat shaped cord spool
• cord, e.g. masonry cord
• a creepy, hairy spider

Start with printing the brackets and the spool / winch head. You will find the resources attached or on Tinkercad.

For the spool head, choose an infill (type and amount) that holds screws if the screws are a bit longer. For the brackets I recommend an infill in the area of 70% and if the motor is higher, remove the bottom part to fit it in.

The servo brackets used in the 3D design are from Tinkercad’s library. The 360° one was adjusted for the non centered mounting hole.

If you do not have a 3D printer, you can use duct tape to attach the 360° servo to the 180° servo motor. Please makle sure that the 180° servo is set to center position. For the spool head you could use cardboard and a big knob. The diameter of the round plate is 100 mm (or 4"). The knob has a height of 35 mm (roughly 1⅓"). Its diameter at the bottom is 60 mm and 56 mm on top, so slightly narrower on top so that the cord falls off easily.

1. Screw the 180° servo bracket onto a piece of wood and make sure that the mounted 360° bracket with the spool can tilt back and forth.
2. Clip the 180° servo into the bracket.
3. Glue or screw a cross-shaped servo arm onto the 360° servo bracket, maybe do both.
4. Attach this part (of step 3) to the servo (of step 2) and fasten it with a screw. (You might want to run the code once to set the tilt servo into the wind up position.)
5. Clip the 360° servo into the tilting bracket.
6. Connect a cross-shaped servo arm to the spool and fixate it either with screws or a soldering iron.
7. Attach this part (of step 6) to the servo (of step 5) and fasten it with a screw.
8. Drill a small hole into to spool head, directing it to the servo arm, so that you can attach a cord at the back and the knot does not interfere with the tilting servo bracket.

Wire the ultrasonic module, the PWM driver and the micro controller using the wiring diagram. Make sure that the input voltage goes via the PWM driver and not via the micro controller’s USB port.

You can test drive the setup via the USB port but do it either with servos detached or using 9g mini servos.

1. checkout the code from GitHub
2. open Arduino IDE and open the project
3. install the following libraries
4. NewPing
5. PCA9685 16-Channel PWM Driver Module
6. change the configuration
7. trigger distance
8. spool angles for released and windup states
9. time needed to tilt back the spool
10. windup time based on the length of your cord
11. compile and flash it to the micro controller

The spider is triggered is the measured distance is between 3 cm and the configured trigger distance. Feel free to change the minimum distance up, so that you can prevent the trigger while passing close by. Do not set it to 0, because there are a lot of false measurements with 0 cm that would trigger the spider release continuously.

Optionally you can install a button to trigger the spider manually, for example using your door bell and the trigger button. This also works if you do not attach the distance sensor.

Now it is time to position the release mechanism and spider. You can have a direct release, for example above a door, or an indirect one to hide the mechanism better.

Guesstimate the time needed for retraction. Measure the trigger distance and the angles (or guess them). Enter everything into the configuration.

You need to adjust them based on tilting of the complete mechanism. In my example you would need to subtract 90 degrees, because the PWM library uses -90 to 90° instead of 0 to 180°.

Power your device and enjoy!

In my first attempt the cord twisted itself reducing the length until it got entangled, did not fully go off the spool head and broke the tilt bracket while winding up. That is why you see duct tape in the foto. Might be good to use duct tape anyways.

If you guide the cord via a pulley on top, make sure you have a spider that can rotate freely without touching the facade and attach a swivel rotator so that the cord can spin.

I would recommend to use the direct drop with a swivel rotator, if you use giant spiders that touch the facade.