How to Find MOI Through CG Without Knowing the CG Location

Why measure Moment of Inertia (MOI) through the Center of Gravity (CG)? When an object is free to rotate, it will rotate around an axis passing through its center of gravity. Therefore it is essential to know moment of inertia through center of gravity to assess the flight characteristics of a payload. The MOI about […]

Read More

How to Calculate Product of Inertia From Moment of Inertia Measurements

Product of inertia (POI) is the characteristic of an object that causes dynamic unbalance. Knowing the POI of an object is essential to determine some of its flight characteristics, such as its tendency to wobble. Knowing POI in all planes allows determining the principal axes of a payload. How to measure product of inertia? Product […]

Read More

A New Spin Balance Machine

This page describes a new low-speed vertical axis aerospace balance machine that takes advantage of recent advances in technology. This machine measures moment of inertia (MOI) in addition to product of inertia (POI) and center of gravity (CG) offset. Spin speeds as low as 15 RPM yield useful results. This machine has a number of […]

Read More

Using the “Moment of Inertia Method” to Determine Product of Inertia

Product of inertia is generally measured using a spin balance machine. In this type of machine, the object is rotated at a speed of about 100 RPM, and the reaction forces against the upper and lower spindle bearings are measured. Product of inertia is then calculated automatically by the machine’s on line computer, using formulas […]

Read More

Pan Weighing vs Moment Weighing

The terms used in turbine blade balancing can be confusing. The two main terms used are pan weighing and moment weighing. What is Pan Weighing? Pan weighing simply means measuring the mass of the blades. This could be called weighing the blade. We call it pan weighing to avoid the confusion with moment weighing. Pan […]

Read More

Improve Your Sensor Image With Balance

This paper reviews the properties which inherently limit the image quality of a gimbal mounted optical imaging system. It further describes how image quality is degraded by external influences, particularly vibration, in the supporting vehicle. The primary emphasis is to quantify, through physical principals, and verify, through experimental demonstration, the degree of static balance required […]

Read More

Choosing the Right Gimbal Balance Machine

December 28, 2020

Choosing the Right Gimbal Balance Machine The two primary factors affecting selection of a Space Electronics Gimbal Balance Machine are weight of the gimbal and its unbalance tolerance. Maximum gimbal weight.   The machine must accommodate the maximum weight and size of the gimbals to be balanced. However, it should be no larger than necessary since large […]

Read More

Using a Spherical Air Bearing to Simulate Weightlessness

August 12, 2020

It is important to test the attitude control systems on satellites before they are launched in space. Traditionally this has been done by dropping the satellite, and firing the thrusters before the satellite makes a soft landing in a net. This method only allows a few seconds of testing and does not lend itself to […]

Read More