The design solution for a portable, battery-powered giant mast and camera for aerial coverage of sporting events required more than the average amount of ingenuity and a mix of servo and hydraulic motors interfaced to a single motion controller.
Building a camera mast that extends as high as a 12-story building with the dynamic stability to support a full-sized 50-kg camera at speeds of 2m per second in high winds is a challenge. But the design requirements also included stowing and operating the mast from a single-axle trailer and self-contained operation from batteries.
Trio Motion Technology's MC206X motion controller provides position and stability control for a 30-m camera mast that provides sweeping high-angle aerial shots for film and TV. The Vortex Aerial Mount Camera System was developed by cameraman Matthew Gladstone of Cammotion and automation specialist Machinery Control Systems (MCS).
The most impressive part of the Vortex is the design of the mast itself and the motion control system that smoothly positions the mast and provides the high stability control required during filming. Stabilization control is accomplished using four Kevlar guy ropes fixed at the top of the mast and controlled from servomotor driven geared winches bolted to outriggers on the trailer. The guy ropes are independently tensioned in tight synchronization with each other, the main mast winch and camera position.
MCS initially tried torque control on each guy rope but that resulted in adding unwanted deflection to the mast under strong wind conditions where unequal forces resulted in excessive torque demand as the control system tried to correct the error.
The solution was to use the controller in position control mode with the effective length of each guy rope precisely maintained relative to the height of the mast as it travels up or down. The wind force on each side of the mast may vary, but a combination of tensioned guy ropes, with exactly the same length, maintains optimal mast stiffness without adding deflection.
To meet the requirements for self-powering the trailer and battery operation, all components needed to be as energy efficient as possible. Hydraulic motors fitted to each wheel are independently controlled to drive and maneuver its 3,400-kg payload. Four outriggers used to level the trailer are also hydraulically powered. The hydraulic power packs include variable speed drives for the pumps.
"The decision to use battery power had a major influence on the design and choice of components of the electrical and control system,"says Tim Oxtoby, managing director of MCS, who designed the control system. He says they used a mix of variable speed and servo motors and a 220V, three-phase supply to maintain the power required. Controlling the hydraulics from the same source allowed them to effectively manage the entire system in a seamless way.
Since the hydraulics and servo motors are not used at the same time, switching the control to each system saves costs by using just one MC206X with an optional daughter board for five axes of servo control.
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