Transcript Belts vs Gears - Penn State Mechanical and Nuclear Engineering

ME240/106S: Product Dissection - Appliances
Drill Dissection
What’s so interesting about a drill? It’s got lots of good
stuff in it - electric motors, gears, bearings, etc
It is a good example of an electro-mechanical
power transmission system, and it is also an
example of a machine tool (it drills holes)
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ME240/106S: Product Dissection - Appliances
Major Drill Components
Electric
Motor
Gears
(Transmission)
Chuck
Brushes
Handle
Bearings
Trigger
Switch
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ME240/106S: Product Dissection - Appliances
Bearings – Two Common Types

Bushings - simple, cheap, limited life, porous material
such as “Oilite” which holds oil like a sponge

Rolling Element – support axial or radial loading, long
life, grease or oil-filled, various types of seals, readily
available from standard product catalogs, ex. ball bearings
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ME240/106S: Product Dissection - Appliances
Roller Bearings
Needle
Roller
Tapered Roller
Spherical Roller
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ME240/106S: Product Dissection - Appliances
Rolling Element Bearing Parts
Outer Race
Inner Race
The parts and nomenclature
for a Ball Bearing
Bore
Ball
Cage or Separator
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ME240/106S: Product Dissection - Appliances
Bearings -continued

Hydrodynamic or Sleeve - oil filled, “no” wear, radial
or thrust, common in automobile engines (e.g., crankshaft
bearings)
Rotating Shaft
Shaft Rides On
Oil “Wedge”
Sleeve Bearing
Oil Filled Cavity
A typical radial clearance
is on the order of .010”
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ME240/106S: Product Dissection - Appliances
Types of Gears
Parallel Axis Gearing
A - Spur gears, external contact
B - Spur gears, internal contact
C - Spur, Rack and pinion
D - Spur, Helical gears
E - Herringbone
F - Pin gear
ref. 4
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ME240/106S: Product Dissection - Appliances
Types of Gears - continued
Non-parallel or
non-intersecting axis gearing
G - Bevel gears
H - Spiral bevel
J - Crown bevel
K - Spiral gears
L - Worm and wheel
M - Hypoid gear
ref. 4
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ME240/106S: Product Dissection - Appliances
Gears - continued
a -Epicyclic train; the gear wheel C is fixed
and the arm D moves around its axis at A,
the wheel B will have a retrograde motion
and the wheel A a faster motion in the
direction of the moving arm; if the wheel A is
fixed, B and C will have unequal forward
motions.
(a)
(b)
A
B
D
G
b -Sun and planet gear on a winch.
C
c -Planetary motion as applied to an appleparing machine.
A
(c)
(d)
d -Epicyclic bevel gears; an arm FG is fast on a shaft AA ; bevel wheel B is
loose on this arm; bevel wheels D and C are loose on the shaft AA ;
differential motions of the arm FG around and with shaft A , or, by making
the arm loose on the shaft, a differential motion of the shaft and arm can be
obtained.
ref. 4
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ME240/106S: Product Dissection - Appliances
Gear Transmissions
Planet gears (4)
Ring Gear (can be stationary)
Sun Gear
Planetary Gearboxes give high reduction (between
sun gear and planet carrier),
compact size, can distribute or add
power
Planet
Carrier
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ME240/106S: Product Dissection - Appliances
Gear Transmissions
Output
Shaft
Two Stage, parallel shaft,
helical gearset from the SKIL electric drill
Ball
Bearing
Bushing
Input Pinion
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ME240/106S: Product Dissection - Appliances
Electric Motors
Commutator
AC - most common type for
power applications,
simple, cheap, constant
speed operation
DC - easily controlled,
variable speed operation,
with or without brushes,
also function as
generator
Brushes (2)
Stationary Windings
(stator)
Armature (rotating unit)
Internal view of the “Universal” motor
used in the SKIL electric hand drill
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ME240/106S: Product Dissection - Appliances
General Types of Electric Motors

Permanent Magnet DC
– Permanent magnet used in stationary field, rotor (armature)
consists of windings, switching magnetic polarity to keep the
motor turning, brushes make contact with commutator – only
runs on DC and speed is proportional to input voltage

Brushless DC
– Magnets are in the rotor, windings in the stator, polarity
switching of the windings is done externally by additional
circuitry, no brushes to wear out, no sparking or electrical
noise –only run on DC; speed proportional to input voltage
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ME240/106S: Product Dissection - Appliances
General Types of Electric Motors

Universal motor
– Same as a permanent magnet except wound coils (electromagnet) replace the stationary permanent magnet; they will
run on AC or DC and are most commonly found in electrical
appliances as they are cheap and easy to vary speed

AC Induction motor (Tesla’s genius)
– Wound coils in the stator, rotor has no magnets or coils, just a
stack of steel laminations, speed is proportional to frequency
of AC, making it difficult to vary speed of the motor
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ME240/106S: Product Dissection - Appliances
Universal Motor - AC and DC
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ME240/106S: Product Dissection - Appliances
Permanent Magnet
DC Motor Operation
Force generated F = (I x B) L
B = magnetic flux density
I = current in wire
L = length of conductor
+
-
Commutator
(rotates with coil)
F = force
I
Brush
F
B = magnetic
field
Permanent
Magnet
L
I = current
Permanent
Magnet
S
N
B
Coil (single conductor shown)
Build your own motor: http://www.exploratorium.edu/snacks/snackintro.html
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ME240/106S: Product Dissection - Appliances
How does a chuck work?
Source: Macaulay, D., 1998, The New Way Things Work, Houghton Mifflin Company, Boston, MA.
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