Prototype, Updated

Updated Prototype:

A 131:1 DC motor from Pololu has been mounted to the back of the AFO shaft (Figure 2). Of the motors already purchased for the course, this motor had the highest gear ratio available and so will provide the highest torque.  In addition to mounting the motor to the crank, we have added an attachment location for a potentiometer along the same axis as the motor shaft. The potentiometer will be used to sense absolute angular position of the crank. We have re-worked the connection between the footplate and the shaft and now have two options for the four-bar link lengths. The footplate, a post-op shoe consisting of a skid-resistant, stiff sole and a nylon upper mesh with adjustable velcro straps, has been attached via screws into the sole.

We have begun work on the electronics portion of the system, designing a motor control circuit and writing a simple PD control scheme. External power is provided through a AC to 12V DC power supply which is wired to a Sabertooth 2x5 dual motor controller. The Sabertooth controls the power to the motor based on a Pulse Width Modulated (PWM) signal received from an Arduino microcontroller which receives an input from the potentiometer. Before connecting the motor to the control circuit, we first powered it by a 9V battery, verifying that it could overcome the linkage friction and rotate the footplate. Then we disconnected the motor from the AFO linkage and verified that the motor control circuit performed as expected, moving the motor shaft in the desired direction.

Figure 1. Updated prototype including electronics and preliminary circuits.

Figure 2. Draft of Final Mechanical Assembly