Reflected Inertia?

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Posted by P.J. Baker at 04/24/2001 12:29 PM EST


Engineer on team #177, Bobcat Robotics, from South Windsor High School and International Fuel Cells.


In Reply to: Reflected Inertia?
Posted by ChrisH on 04/24/2001 11:27 AM EST:



I'm not truly a motors guy, but it goes something like this:

The reflected inertia is the inertial load that the motor sees through the system's drive train.

Taking a robot as an example, and looking at it from the wheel (the end of the drive train) a torque must be exerted on the inertial load of the robot to achieve angular acceleration of the wheels (Torque = J (inertia) * alpha (angular acceleration)) which will result (with good traction) in linear acceleration of the robot.

Because of the mechanical advantage of the drive train (equal to the gear reduction), the inertia that the motor actually "sees" is much smaller than the inertia that you would feel if you personally tried to move the robot by turning its wheels. To the best of my knowledge, this reduced inertia is known as the "reflected inertia" of the system.

Please note that I've simplified things a bit here, and probably left a thing or two out, but I believe the basic concept is right. In designing sytems with motors, people will often try to match the motor inertia (armatures, windings, etc.) to the reflected inertia of the system. I think that this is basically analogous to impedance matching in electronics design.

Hope that helps. I also hope that someone like Joe J. who works w/motors on a daily basis comes along and does the expanation a little more justice than I did.

P.J.