Linear Actuators

Don't let the fancy name intimidate you, linear actuators are simply like a motorized screw that extends as it gets turned. They provide an adjustable length support arm for all kinds of moveable surfaces like solar panels. Tracking devices depend on linear actuators to move solar panels or mirrors. The actuators that have been developed for large, and now largely obsolete, satellite dish systems are perfectly suited for use with solar tracking systems. With a range of motion from 1 to 3 foot, and able to handle over 400 hundred pound loads, these are great for small and medium sized tracking systems. They have a long track record, are designed for weather exposure, and require almost no maintenance.
Most actuators feature something like a reed switch system that gives a certain number of pulses per inch of travel to help a microprocessor keep track of the actuator position. By knowing the pulses per inch, and the current pulse count since the arm started along with the shortest arm length, the computer can calculate the arm's length at any given moment.
While we could use something like a pulley and attach the actuator to a belt to get a linear rate of rotation from the actuator motion, the most practical way is usually with a control arm, which makes the rotation follow the laws of trigonometry.

The points where the actuator arm is mounted at each end form a triangle with point at the axis of rotation. If we measure the distance from the axis of rotation for each of the mounting points, then we now know the length of three sides of a triangle. The law of cosines from geometry can be applied to solve for the angles, and now we know where our panel is pointing!
Gear head motors cost hundreds of dollars and are subject to high torque stress which linear actuators avoid, while actuators take up more room and are less visually appealing. From a functional and value perspective linear actuators represent the best way to move your solar tracking device.

These are some of the linear actuators from Venture Manufacturing Co. that we are particularly fond of.

Their stock actuators can easily provide better than 0.5 degree accuracy, and they have stepper motors and other options for stronger requirements.