Balancing a Gimbal - Advantages of the Space Electronics method

The Space Electronics Method of Balancing a Two-Axis Gimbal: The seeker or other type of gimbal is mounted in the machine so that the gimbal base is against a vertical mounting plate and the two axes of the gimbal are oriented at 45° from the horizontal. The gimbal is then rotated to each of the four positions shown in Figure 1. The X and Y coordinates of the CG position as projected onto the horizontal machine axes are measured. If the gimbal is balanced, its CG will not move as the gimbal is rotated about its own axes. Because of the 45° orientation, there is a unique relationship between the change in position of CG and the projection of its coordinates on the horizontal plane of the machine. This allows the machine's computer to analyze the data and compute the location and magnitude of the unbalance relative to the coordinates of the gimbal.

Gimbal Rotated to four positions Figure 1 - The Gimbal is rotated to four different positions.

All measurements are made in one machine setup, which allows unbalance about both rotation axes to be determined simultaneously.
Unbalance moment is reported directly in terms of gimbal coordinates.
The gimbal is static during measurement, eliminating the effects of bearing friction and the possibility of damage which can occur using dynamic methods .
Fully assembled gimbals (complete with wiring) are tested, significantly improving accuracy over methods which balance individual components.
Our force rebalance technology provides highest sensitivity combined with ruggedness and high speed.
Optional custom software can provide a printed report of optimized weights and locations required to reduce unbalance to acceptable levels. Trial and error balancing is eliminated.

TYPICAL PRINTOUT OF GIMBAL UNBALANCE

Unbalance along Axis B	7.3 g-cm
Unbalance along Axis C when rotating about Axis A	4.1 g-cm
RESULTANT OF ABOVE [unbalance about A AXIS]	8.4 g-cm
UNBALANCE ALLOWED	4.0 g-cm
>> GIMBAL UNBALANCE EXCEEDS TOLERANCE <<

Unbalance along Axis A	2.1 g-cm
Unbalance along Axis C when rotating about Axis B	2.6 g-cm
RESULTANT OF ABOVE [unbalance about B AXIS]	3.4 g-cm
UNBALANCE ALLOWED	4.0 g-cm
>>THIS AXIS WITHIN TOLERANCE<<

Custom weight correction software After the

machine measures the unbalance about the gimbal axes, it is necessary to choose the proper ballast weights required to bring this unbalance within tolerance. If the ballast weight locations were directly in line with each axis, then this would be a simple matter. However, usually the locations do not fall directly on an axis, resulting in a moment change in more than one axis when a weight is added to the gimbal. This interaction makes the balancing solution very difficult to solve. If this is done by trial and error, it can take as much as 8 hours to balance a single gimbal. Space Electronics can provide custom software which requires less than 10 minutes to examine all combinations of available weights and locations and presents the best solution. This software is unique to each gimbal. If you are interested in a quotation, we will need specific information about your gimbal. Contact our sales department.

TYPICAL CORRECTION WEIGHT PRINTOUT
WEIGHT LOCATION	NUMBER OF WEIGHTS	WEIGHT PART NUMBER
1	1	1736 AX
3	2	1738 A
4	1	1921
5	3	11621-3
6	1	1736 AX

To balance the gimbal, the operator mounts one 1736AX weight at location 1, two 1738A weights at location 3, etc. After mounting correction weights, the operator re-measures the gimbal to verify that it is within unbalance tolerances.

ADVANTAGES OF THE SPACE ELECTRONICS METHOD