Introduction and What are Mass Properties - RC Groups
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Jan 26, 2013, 04:20 PM
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Introduction and What are Mass Properties

I am Daniel Otlowski. I have been in the RC multicopter world for five years. What attracted me to this hobby was the diverse skill set required to become proficient. The skills naturally dovetailed with my line of work at Space Electronics where I've worked since 1979.

At Space Electronics we design and build instrument that measure CG, MOI, Gimbal Balance, POI (dynamic balance), Blade balance, etc. In many respects my work experience puts me in a position to advance the ball, spreading the knowledge to beginners and advanced hobbyists. I find that a lot of my posts are related to teaching how physics applies to multirotors and to convey the subtleties of terminology. My infrequent posts are scattered about as I usually try to gently push information out there. I thought I would start this blog to gather these snippets in one place.

The blog is meant to be read in order

Mass Properties are fundamental physical properties of matter. All manner of objects from the atomic level to large man-made assemblies and naturally occurring objects can be characterized by their mass properties.

They include:
  • Mass and Inertia (provided as two separate thoughts although essentially the same)
  • Mass – the amount of matter – often thought of as ‘weight’ when in the presence of a gravity field
  • Inertia – resistance to a change in motion – Inertia is that quantity which depends solely upon mass and vice-versa
  • Moment of Inertia – resistance to rotational motion – rotational inertia dependant not only on overall mass but on the distribution of that mass relative to the center of rotation.
  • Center of Gravity – quantifies the distribution of mass in an object – the static mass balance point in three dimensions
  • Product of Inertia – dynamic imbalance – objects may be statically balanced while remaining unbalanced when spun. It is possible to use dynamic means to correct a static imbalance, but not vise versa.
The mass properties of an object are absolute and are fundamentally independent of the surrounding environment. A reasonable way to visualize them is to assume that they are defined and quantified in the gravitational less vacuum of space. Although earthly environmental factors such as gravity, atmosphere, friction, mechanical efficiency losses, etc, do not change an object’s mass properties; these factors can affect how the object interacts in the real world, and how we interpret that interaction.
Last edited by otlski; Oct 05, 2013 at 10:38 AM. Reason: test
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