Shown below is a mock-up of the currently mechanical axis system
Mechanical Mounting CAD Mockup
Exploded View
Description
Dimensions : 12'' x 12'' x 7''
Weight : ~7kg w/o electronics (negliable)
Tracking Design Goal : steady - state accuracy of 1 degree has been satisfied. Transient response a WIP
The above system is the currently implemented platform system. The dual-axis platform is controlled
with two stepper motors, illustrated in purple, driving a gearing system, shown in blue. The gears were
necessary in order to reduce the full-step angular distance of the stepper motors being used (1.8 degrees)
for tracking accuracy, and to increase the avaliable torque of the motors to drive larger loads. Necessarily,
controlling the position of the system requires accurate measurement of that position. To that effect, the small
red rectangle mounted below in the main plate in the mockup is an interial measurement unit (a Razer IMU from
sparkfun), with firmware to
translate the 9DOF accerlation and rate angle information into a true AHRS, outputing roll, pitch, and yaw to
a SAM3U-EK development board.
The SAM3U-Ek and associated motor control electronics are depicted as the other red blocks contained in a housing on the base of the platform. The SAM3U-Ek is reponsible for reading the positional data output by the IMU (and in the future, the GPS), computing the necessary motor control sequences, and outputing those sequences through two parallel stepper motor drivers (Pololu A4988 breakout boards). Currently, in a block-diagram sense, the system can be thought of as measureming position and reporting it back with unity feedback. The step-gain, which can be thought of as a loop gain, can be controlled throught software. If active compensation is necessary as further testing continues, software-defined compensation methods can be implemented, such as a simple PID controller.
Features
- Dual-axis systems allows full-range movement/
- Circumferential control contacts or limited revolutions with cable system/
- Motion of axes corresponds intuitively to horizontal coordinates/
- SAM3U-EK has extensive library support, and numerous I/O channels for peripherials.
- Open platform allows wide range of loads to be mounted.