Hi,

This Instructable covers the creation of a robotic backpack, designed so that I could stroll around our town scaring people at will for Halloween.

Its a bit quick and dirty as I'm not feeling well tonight, so I will come back and elaborate in a few days

The basic idea was an outreach program from the local genetic research facility, showing that genetic material could be safely transported through the community using specialised containers.

All a bit cheesy, but that is what Halloween is all about isn't it :)

Step 1: Shell

The basic shell is a wooden box with supports and gaps in the appropriate places for the motors, mechanisms, etc

The main parts are

Eyes - ping pong balls on a mechanism activated by a hobby servo.

Fingers - bamboo fingers again deployed and retracted by two servos.

Flip out head - I searched through my old motors and found one that I could easily attach an arm to allow the "charging" of a bungee cord.

Step 2: Eyes

Two nails were passed through a piece of wood which acted as the supports for the ping-pong eyes. two arms were attached to the top of the balls which were linked together and actuated by a servo.

Step 3: Fingers

The fingers were made out of bamboo, using bent nails and glue to get the desired joints.

Lots of time was spent getting the right arc for the fingers to come out through the top of the box as realistically as possible.

Two normal hobby servos were used, one per hand. I had to open one servo and reverse the motor contacts and the contacts to the internal pot to make it mirror its normal operation. This was due to the mechanics of the two finger units and how they were installed in the system.

Step 4: Head

The head was the most tricky part of the system.

I used a bungee cord and an arm to act as the spring-loading for the head to jump out of two doors in the top of the box.

Lots of cardboard models and trial and error helped here to get the timings right and have enough force to swing open the top doors.

Step 5: Electrics and Final Trimming

The electrical circuits were pretty simple, limit switches and relays in the box for the head unit.

Lots of wiring for LED external illumination and the LED eyes.

A control box which housed the fire button, 555 servo control circuit and switches for the fingers, eyes, etc.

Many hours spent making everything rigid and cladding the whole unit with silver-backed insulation board.

An amplifier circuit was used with a large speaker to allow my MP3 player to give out appropriately grisly sounds and a few techy sound-bites.

The battery used was a LIPO cell 4200mah which lasted all night.

Enjoy the video that my 9 year old daughter took of the unit in action.

P.s if you get bored with teh video, skip to 2:15