3.3 Explain the Electrical devices

3.3.1 Discuss about the DC Motor

•      Widely used in robotics because

–     small size and high energy output. 

•      Excellent for powering the drive wheels of a mobile robot as well as powering other mechanical assemblies.

•      Provides precision control of speed, driven by a direct current. 

•      For a particularly high ratio of torque to inertia, the Brush DC Motor has the potential to supply three to four times more torque than it’s rated torque. 

•      Can even provide up to five times more, without stalling. 

•      Offers stable and continuous current, using rings to power a magnetic drive that operates the motor’s armature. 

•      One of the earliest used motors, the Brush DC Motor is commonly used because of the ability to vary the speed-torque ratio in almost any way.

DC motors Components 

•      Field pole (stator)

–     North pole and south pole

–     Receive electricity to form magnetic field

 

•      Armature (Rotor)

–     Cylinder between the poles

–     Electromagnet when current goes through

–     Linked to drive shaft to drive the load 

 

•      Commutator

–     Overturns current direction in armature

How does a Brush DC Motor work?

•      consists of two magnets facing the same direction, that surrounding two coils of wire that reside in the middle of the Brush DC Motor, around a rotor. 

•      The coils are positioned to face the magnets, causing electricity to flow to them. 

•      generates a magnetic field, which ultimately pushes the coils away from the magnets they are facing, and causes the rotor to turn. 

•      The current shuts off at the rotor and makes a 180 degree turn, causing each rotor to face the opposite magnet. 

•      As the current turns on again, the electricity flows oppositely, sending another pulse that causes the rotor to turn once again. 

•      The brushes that are located within the Brush DC Motor turn it off an on when instructed, by transferring the electricity from the rotor.

 (source:http://www.anaheimautomation.com/manuals/forms/brush-dc-motor-guide.php#sthash.e8uQa9P5.dpbs )

Advantages and Disadvantages

·         The Brush DC Motor has a simple construction, therefore may not require a controller. When a controller is chosen, it is typically a simple and inexpensive drive design. 

·         Understandable design technology facilitates in the quick application

 ·        The design of the Brush DC Motor is quite simple, in that a permanent magnetic field is created in the by either of two means; permanent magnets or electro-magnetic windings

·        

      The field is created by permanent magnets, a Brush DC Motor is said to be a "permanent magnet DC motor" (PMDC). If created by electromagnetic windings, the DC Brush Motor is often said to be a "shunt wound Brush DC Motor" (SWDC). Today, because of cost-effectiveness and reliability, the PMDC motor is the motor of choice for applications involving a fractional horsepower Brush DC Motor, as well as most applications up to about 2.0 horsepower. 

·         Opposing the stator field is the armature field, which is generated by a changing electromagnetic flux coming from windings located on the rotor of the DC Brush Motor. The magnetic poles of the armature field will attempt to line up with the opposite magnetic poles generated by the stator field. Next, the section of the rotor where the electricity enters the rotor windings is called the commutator. The electricity is carried between the brush motor rotor and the stator by conductive graphite-copper brushes (mounted on the rotor) which contact rings on stator.

 (source:http://www.anaheimautomation.com/manuals/forms/brush-dc-motor-guide.php#sthash.e8uQa9P5.dpbs )

Disadvantages of an DC Motor

·         A Brush DC Motor is less reliable in control at lowest speeds

·         A Brush DC Motor is physically larger than other motors producing equivalent torque

·         A Brush DC Motor is considered high-maintenance, which is not true of brushless DC motors

·         A Brush DC Motor are vulnerable to dust which decreases performance

  (source:http://www.anaheimautomation.com/manuals/forms/brush-dc-motor-guide.php#sthash.e8uQa9P5.dpbs )

Types of DC motors

•      Permanent-magnet motors

•      Brushed DC motors

•      Brushless DC motors

•      Switched reluctance motors

•      Coreless or ironless DC motors

•      Printed armature or pancake DC motors

Figure: Industrial Robot that uses DC Motors

VIDEO: A challenge to Polytechnics students in Malaysia.....an Arm Robot, using toys DC Motors and PVC Pipes!!!   Make one,   Ill give you an A!

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