Unbalanced Gimbal under acceleration - RC Groups
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Jan 27, 2013, 08:51 PM
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# Unbalanced Gimbal under acceleration

Continuing with the 2D view, we will now show what happens to the imbalanced innermost axis (the camera) when a forward acceleration is applied. The applied acceleration in this case is a straight-line translational acceleration. For our example, we have no restoring force normally provided by closed loop torque motors. We are simple applying acceleration disturbance and observing the reaction motion.

 06 Acceleration with Imbalance (0 min 4 sec)

The 2D CG can be expressed in moment units (torque units), say Kg-mm for example. Let's say our camera weighs 1 Kg and the CG is 10 mm offset from the pivot relative to the direction of motion. This creates a normal moment of 10 kg-mm. Now, let's say the acceleration experienced is 3 G (gravity), the torque initially created would thus be 30 Kg-mm.

Let's take note of a few important things here. First, in the absence of translational acceleration, there is nothing making the gimbal want to rotate off target. Second, any torque from acceleration disappears once a steady state velocity is obtained. Third, the torque via acceleration becomes less and less as the gimbal rotates in response. This continues until the CG is located "behind" the pivot in the acceleration shadow. Forth, if the CG was coincident with the pivot, there would be no moment arm for the acceleration to act against, thus the gimbal does not respond to translational accelerations.
Last edited by otlski; Jan 28, 2013 at 08:02 PM.