Reciprocating Saw Dissection: Motor Description

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Reciprocating Saw DissectionMotor Description

• Thomas Snowdon

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DC Electrical Principles

• When power is from a battery the current is
  called DC for direct current
• Motors that operate from battery power are called
  DC motors
• Current flow from a battery is always in the same
  direction
• Current magnitude in a coil is dependant on
  battery voltage and wire resistance

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Design Principles

• Driven by electromagnetics
• Like magnetic poles repel, opposite magnetic
  poles attract
• Current passed through a coil of wire produces a
  magnetic field
• Changing the direction of current in a coil
  reverses the magnetic field
• The amount of current in a coil will determine
  the strength of the poles or magnetic field.

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Motor Construction

• Major Components
• Frame
• Stator Coils
• Rotor
• Commutator and Brushes

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• Frame is made of metal and supports the other
  parts
• Stator can be made of either permanent magnets or
  coils of wire on a steel core
• Rotor is made up of a shaft, a set of wire coils,
  and the commutator
• Rotor shaft is supported by bearings in the frame
• Shaft extends out of the motor to drive tool

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• Commutator connects the coils to the brushes
• Brushes connected to the battery voltage
• Coil polarity changes as the commutator turns

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Operation

• Motor creates a rotating motion from the battery
  power
• As the motor rotor turns the commutator switches
  the current flow in the rotor coils
• Motor shaft has a gear attached to drive the next
  piece of the tool
• Speed of the motor is dependant on the current
  flow through the coils

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Advantages and Disadvantages of DC Motors

• Advantages
• Variable speed control
• Portable
• Can handle heavy torque loads
• Disadvantages
• Complex to build and expensive
• Not as reliable as other motors
• Difficulty keeping a constant speed

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Conclusion

• The motor used in this tool is a DC type motor
• Operates on battery power
• Runs at variable speeds
• Can handle heavy torque loads created by tool use
• References
• Fitzgerald, A. E., Charles Kingsley, and
  Alexander Kusko. Electric Machinery. 3rd ed.
  McGraw-Hill Book Company, 1971.
• http//www.ni.com/

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References

• Fitzgerald, A. E., Charles Kingsley, and
  Alexander Kusko. Electric Machinery. 3rd ed.
  McGraw-Hill Book Company, 1971.
• http//www.ni.com/