Fans As Actuators - Revision history

ScottM: /* Usage */

2008-12-22T20:00:57Z

Usage

2008-12-20T03:41:54Z

Driving and Controlling

2008-12-20T03:26:09Z

Phase Lag

2008-12-20T03:21:41Z

Introduction

2008-12-20T02:56:42Z

Most Common Types of Fans

2008-12-20T02:48:18Z

Axial (Propellor)

2008-12-20T02:48:11Z

Most Common Types of Fans

2008-12-20T02:45:48Z

Centrifugal (radial)

2008-12-20T02:45:37Z

Driving and Controlling

2008-12-20T02:45:28Z

Types of Fans

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 Fans may be used as primary actuators for mobile robots intended to move without direct physical contact with a surface (floor, ceiling, etc).  In particular, applications may include flying and hovering agents such as planes, helicopters, blimps, and hovercraft.
-It is important to note that fans operate much differently than wheels or legs as they produce motion as a "force source".  Without direct physical contact to a surface or ground, this will result in an acceleration with low friction.  To command the position of the agent, one will need to devise a double integrating controller.
+It is important to note that fans operate much differently than wheels or legs as they produce motion as a "force source".  Without direct physical contact to a surface or ground, this will result in an acceleration.  To command the position of the agent, one will need to devise a double integrating controller.
 ===Rating===

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 ==Driving and Controlling==
+Driving a prepackaged fan is simply a matter of controlling the motor.  Most fans will be driven by brushed DC or brushless DC motors.  In many applications, fans are low power, and can be driven by prepackaged H-bridge circuits or with a single MOSFET.  Note that if the fan you have selected is unidirectional, there is no advantage to using an H-bridge over a single MOSFET.
+Most computer cooling fans are designed to minimize EMI, and hence are actuated by brushless DC motors.  Inside, they have their own brushless DC motor controller that adjusts the speed of the fan as a function of the input voltage.  Although the controller accepts variable input voltages, the controller only functions for a single polarity and hence drives the fan in a single direction.  From experimentation, it appears that the motor is not harmed by applying a reversely biased voltage.
 ==Important Practical Considerations==

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 To attain true bidirectional motion, one will typically have to select a bidirectional motor and propeller blade separately (avoid prepackaged fans).  R/C airplane and helicopter hobby sites typically offer good starting points for such applications.
-===Phase Lag===
+===Time Constant (Phase Lag)===
 One of the most significant practical limitations of using a fan as an actuator is the lag when accelerating the fan.  Accelerating from one velocity to another velocity (increasing/decreasing thrust) physically takes time.  The amount of time is typically proportional to the difference in velocities and can be on the order of seconds.

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 ==Introduction==
+===Usage===
+Fans may be used as primary actuators for mobile robots intended to move without direct physical contact with a surface (floor, ceiling, etc).  In particular, applications may include flying and hovering agents such as planes, helicopters, blimps, and hovercraft.
+It is important to note that fans operate much differently than wheels or legs as they produce motion as a "force source".  Without direct physical contact to a surface or ground, this will result in an acceleration with low friction.  To command the position of the agent, one will need to devise a double integrating controller.
+===Rating===
+Aside from typical input power specifications (voltage / current), the physical performance of a fan is measured by the fan's max flow rate, and max pressure.  Flow rate is the measure of volume of fluid (air) through a given area in a fixed amount of time.  Pressure is the measure of force per fixed unit area.
 ==Most Common Types of Fans==

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 ==Most Common Types of Fans==
+For more information, [http://www.engineeringtoolbox.com/fan-types-d_142.html this link] gives a good overview including pressure/volume comparison graphs.
 ===Axial (Propellor)===
 [[Image:AxialFanPicture.JPG |thumb|150px|right| Axial Fan]]

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 [[Image:AxialFanPicture.JPG |thumb|150px|right| Axial Fan]]
 This type of fan uses a fixed blade that produces airflow parallel to the direction of rotation.  This fan design can be seen in many cooling applications, as it is designed to maximize the volume of air moved.
+<br clear=all>
 ===Centrifugal (radial)===