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This is a project I worked on with Gift Nykayaramba, Minhaz Islam, Negatu Asmamaw and Fabio Berger for the Duke ECE Student Showcase on January 23rd, 2014.
http://www.youtube.com/watch?v=1EKQisgA6HU
http://www.youtube.com/watch?v=67BF7ubbdGc
The goal of the project was to demonstrate remote human-robot interaction using low cost technologies. We decided to implement a user controlled 3D printed arm which would be controlled by a sleeve worn by the user. This sleeve would track the movements in the user's hand and wirelessly transmit them to the motors in the robotic arm.
The 3D Printed hand was printed with files from an open source 3d printable robot project (www.inmoov.fr) and is mechanically driven by 5 King High Torque servos (one for each finger). Instructions for assembly can be found on that site.
The wireless system is quite basic and is based on an arduino sensing system and an Xbee wireless module. The Arduino on the user sleeve is wired to 5 flex resistors attached to the glove and detects the voltage change across it as a measure of how bent the user's fingers are. The arduino then maps these raw values onto a 0-9 scale for easy transmission and then creates a 3 byte information packet for each finger. The 3 bytes are:
- A capitalised letter showing which finger the packet is destined to (eg. 'T' for thumb)
- The value from 0-9 that is converted from an int to a char so as to take only 1 byte rather than 4
- An end of packet delimiter that we chose to be the char '.'
The Xbee module then buffered these packets and sent them out byte by byte over a 2.4GHz frequency spectrum. The receiving Xbee then receives these bytes of information in whatever order they arrive in and sends it to the attached Arduino for processing. The Receiving Arduino begins by popping bytes off the Serial buffer stack and analyses it to see which finger this packet is destined for. To make sure it is the first byte of a valid packet it checks if it is a valid identifying letter and continues only if it is. If not, then it continues popping off the buffer until it finds a valid packet start. It assumes the next byte is the char from 0-9 and converts it to an int and checks whether it is actually between 0-9. If it is not, the checker discards the packet and searches the buffer for a new one. If the number is valid however, the code checks if the next byte is the '.' char to check the validity of the packet and then routes the information to the relevant servo.
This wireless protocol allowed us to achieve a surprising degree of accuracy and decent results upto a range of 200ft (the range of the wireless modules).