Reciprocating Saw Dissection:

Motor Description

Thomas Snowdon

• 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

DC Electrical Principles

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.

Motor Construction

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

• 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

• Commutator connects the coils to the brushes

• Brushes connected to the battery voltage

• Coil polarity changes as the commutator turns

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

Advantages and Disadvantages of DC

MotorsAdvantages:• Variable speed control• Portable• Can handle heavy torque loadsDisadvantages• Complex to build and

expensive• Not as reliable as other motors• Difficulty keeping a constant

speed

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/

References

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

• http://www.ni.com/