Which of the following is NOT a gravity energy source that requires control?

The correct answer is elastic bands, as they do not rely on gravitational energy to operate or exert force in the same manner as the other options. Elastic bands use the potential energy stored in their stretched state, which is released when they return to their original shape. This energy source does not involve the control measures typically necessary for gravity-activated systems, which can pose hazards if not properly managed.

In contrast, camshafts, hydraulic and pneumatic cylinder rods, and counterweights all engage with gravitational forces in their functioning. For example, counterweights are specifically designed to balance or offset loads affected by gravity, requiring careful management to ensure safety during operation. Similarly, hydraulic and pneumatic systems often involve mechanisms that must be controlled to prevent accidents related to the forces of gravity. Therefore, elastic bands stand out as not being a gravity energy source necessitating control.