Mechatronics Design/Implementation (Embedded System)

For the embedded system for the exoskeleton we chose the Stellaris EK-LM4F120XL LaunchPad with a custom booster pack. We used this system instead of an Arduino to reduce the number of batteries needed by the system. With the Arduino we would need a 5v power source for Arduino, and a 12v power source for the motor. The booster pack we used with the TI-Launchpad was designed by Rachel Smith and uses only one battery to power both the motor at 12v and TI-Launchpad at 5v.

The TI-Launchpad is a low power embedded system that can be programmed with an IDE named Keil.  It runs at 80MHz, has 256KB of flash memory, 32KB of RAM, and 2Kb of EEPROM. The 40 GPIO pins can be digital, analog, I2C, or serial lines. The custom booster-pack breaks out the GPIO pins, allowing a 5v, and 3.3v power rails, along with ground rails. It has a power regulator, rated for 40v, which provides 5v to the TI-Launchpad. The battery connected to the booster-pack directly powers the motor. The booster-pack also has an H-bridge used to control the motor. This circuitry allows the system be run off a single battery, 12v for our purpose.

To program the microcontroller, we used a library provided by the IEEE RAS at the University of Texas. This library provides function to generate PWM signals, set motor speeds, and read/write to GPIO pins. This allowed us to control the motor we used on the exoskeleton. In the final model, we provided the exoskeleton with a constant velocity. For future iterations, we could use velocity controller to better match the desired movement.

The motor we chose for the exoskeleton is a Pololu 131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder. This motor had the highest torque of those available to us at the time. However, it was unable to provide enough torque to fully move the exoskeleton. For future iterations, a higher power motor should be used.