Actuators

I've been researching actuators and I've settled on two options.  The first option is to use the light weight inexpensive hobby servos used in rc planes.  This would involve fixing the hobby servos to the frame at or very near individual joints.  The second actuator option is to use a custom built centralized servo bank that is linked to the limbs via wire tendons.  These tendons would be either fed through a system of very small pulleys or though flexible sheaths similar to the sheaths that cover cable tendons on a bicycle.

Both of these options have their advantages and disadvantages.  The hobby servos would be much easier to install and control electronically.  I've already been able to establish that multiple hobby servos can be controlled fairly easily with one Arduino UNO by connecting the servos from an rc airplane to my UNO and using Arduino's servo library.  Also, although most inexpensive hobby servos are not known for being able to move very large loads, I intend to make this robot very light weight, so there wouldn't be a problem if I chose to use this method.  The main issue I would be concerned about would be wearing out the servos.  If I do decide to go with the hobby servos, I will have to find an acceptable balance between quality and price.  For wire tendons the primary advantage would be greater reliability and endurance.  I've been able to find numerous scientific journal articles and PhD dissertations that contain loads of information about materials and designs use in such systems, so I can know which techniques to use for my project.  The major drawbacks for using wire tendons would be the increased complexity and need for specialized parts.  I would need to design gear boxes and plan for and arrange many pulleys.  While not a show stopper, the complexity of wire tendons would definitely change the time-line of this project. 

So far I have not decided which system to go with and have instead decided to order sample parts for both options.  The parts include very tiny wire rope and tiny pulleys from McMaster Carr, and several low cost sample servos from a website in Hong Kong.  The parts from McMaster Carr arrived almost the next day, but it has taken several week to receive the servos.  I will update the blog when I have tested both options.