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Engineering Applications 3004 > Practical sessions - Electrical drill > Flashcards

Practical sessions - Electrical drill Flashcards

1
Q

Main Sub Assemblies of a electrical drill?

A
  • Motor
  • Chuck
  • Ratchet
  • Clutch
  • Gearing and drive shaft
  • PCB
  • Battery
  • Casing
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2
Q

What does the casing do?

A

The casing encloses, secures and protects internal components of the drill

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3
Q

What must the material used for casing be?

A
  • Durable, robust and fluid resistant
  • Resistant to corrosion
  • Non-conductive
  • Non-combustible (does not burn or set on fire)
  • Ergonomic
  • Aesthetic
  • Structural
  • Supportive (secure internals)
  • Accessible (assembly)
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4
Q

What does the PCB and control do?

A
  • The Printed Circuit Board and auxiliary components provide the control to operate all of the drill’s operations
  • The PCB mechanically supports and electrically connects electrical or electronic components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto sheet layers of a non-conductive substrate
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5
Q

What must be included to control the drills operations?

A
  • PCB
  • Wires
  • Switches
  • LEDs
  • Connectors
  • Meet WEEE regulations
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6
Q

What does the Gearing and Drive Shaft do?

A
  • The gearing enables the drill to operate at different
    speeds, both in forwards (clockwise) and reverse (anti-
    clockwise) rotary motion
  • It also transmits the torque to the drill bit via the drive
    shaft
  • The gears will work (be in contact) continuously whilst on
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7
Q

How must the Gearing and Drive Shaft be?

A
  • Wear resistant (hardness)
  • Self lubricating
  • Provide required ratio
  • Frictionless
  • Strong (Strength)
  • Stiff (Young’s modulus)
  • Serviceable
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8
Q

What does the clutch do and what must it’s properties include?

A
  • The clutch disengages the drive (shaft) from the motor,
    enabling the desired gearing to be selected
  • It can also act as a means of releasing the drive when the
    torque is excessive, preventing over-tightening of bolts
    and screws
  • It operates by friction

It therefore needs to be:
- Wear resistant (hardness)
- Strong (strength)
- Serviceable

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9
Q

What does the Ratchet do and what must it’s properties include?

A

A ratchet is a physical mechanism to allow free motion of a drive shaft in one direction; locking when turned in the opposite direction

It’s properties must be:
- Wear resistant (hardness)
- Efficient (frictionless)
- Set with a low torque
- Resist high torque
- Serviceable

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10
Q

What does the Chuck do and what must it’s properties include?

A

A chuck is a mechanism to hold a round cylindrical bar securely and centrally, either to shape it or use it to perform an operation itself

It’s properties must be:
- Wear resistant (hardness)
- Frictionless
- Strong
- Serviceable

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11
Q

What does the motor do?

A

The motor delivers continuous drive force to operate the drill, using energy provided by the battery

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12
Q

What must a motor’s properties include?

A
  • Powerful (Power, torque, speed)
  • Efficient (minimal losses, friction)
  • Heat resistant (It will get hot, thermal conductance)
  • Dissipative of heat (mechanism for removing heat)
  • Meet WEEE regulations (Waste Electrical and Electronic
    Equipment recycling)
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13
Q

How does a Motor work?

A

Anelectric motoris an electrical machinethat converts electrical energy into mechanical energy.

Most electric motors operate through the interaction between the motor’s magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor’s shaft.

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14
Q

What are Motor’s powered by?

A

Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, invertersor electrical generators

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15
Q

What is an electric generator?

A

An electric generator is mechanically identical to an electric motor, but operates with a reversed flow of power, converting mechanical energy into electrical energy

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16
Q

What are the Main Components of an Electric Motor?

A
  • Rotor
  • Bearings
  • Stator
  • Air Gap
  • Windings
  • Commutator
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17
Q

What is a rotor?

A
  • In an electric motor, the moving part is the rotor, which turns the shaft to deliver the mechanical power.
  • The rotor usually has conductors laid into it that carry currents, which interact with the magnetic field of the stator to generate the forces that turn the shaft.
  • Alternatively, some rotors carry permanent magnets, and the stator holds the conductors
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18
Q

What do the Bearings do?

A
  • The rotor is supported by bearings, which allow the rotor to turn on its axis.
  • The bearings are in turn supported by the motor housing. - The motor shaft extends through the bearings to the outside of the motor, where the load is applied.
  • Because the forces of the load are exerted beyond the outermost bearing, the load is said to beoverhung
19
Q

What is a Stator?

A
  • The stator is the fixed part of the motor’s electromagnetic circuit and usually consists of either windings or permanent magnets
20
Q

What is the stator made up of?

A
  • Thin metal sheets, called laminations.
  • Laminations are used to reduce energy losses that would result if a solid core were used
  • Resin-packed motors, used in washing machines and air conditioners, use the damping properties of resin (plastic) to reduce noise and vibration
21
Q

What is the air gap and what is it’s purpose?

A
  • The distance between the rotor and stator is called the air
    gap
  • The air gap has important effects, and is generally as
    small as possible, as a large gap has a strong negative
    effect on performance.
  • It is the main source of the low power factor at which
    motors operate.
  • The magnetizing current increases with the air gap. For
    this reason, the air gap should be minimal.
  • Very small gaps may pose mechanical problems in
    addition to noise and losses
22
Q

What are Windings?

A

Windings are wires that are laid in coils, usually wrapped around a laminated soft iron magnetic coreso as to form magnetic poles when energized with current

23
Q

What is a commutator?

A

Thisis a mechanism used to switchthe input of most DC machines and certain AC machines. It consists of slip-ring segments insulated from each other and from the shaft

24
Q

What does the motor’s armature current supply through and what does it cause?

A

Supplied through stationary brushes in contact with the revolving commutator, which causes required current reversal, and applies power to the machine in an optimal manner as the rotorrotates from pole to pole.

In absence of such current reversal, the motor would brake to a stop

25
Q

What is the rechargeable battery?

A

The battery is the vessel for storing energy-on-demand. The energy delivery must also match the requirements of its use. It must also be sealed for protection.

26
Q

What must it the rechargeable battery be?

A

It must be:
- Powerful (Volts, Watts, Amps)
- Long life-time
- Rechargeable
- Long charge-life
- Corrosion resistant
- Meet WEEE regulations

27
Q

What is a Rechargeable Battery comprised of?

A
  • It is comprised of one or more electrochemical cells
  • It is known as a secondary cell because its
    electrochemical reactions are electrically reversible
  • In other words, after the stored charge has been drained,
    the battery’s chemical reactions can occur again, in
    reverse, to store a new charge
28
Q

What do rechargeable batteries consist of?

A

An anode, a cathode, and an electrolyte

29
Q

Why is demand for rechargeable batteries growing?

A

Demand for rechargeable batteries is growing twice as fast as the demand for non-rechargeable batteries, in part because rechargeable batteries have lower environmental impact and total cost of use than do disposable batteries

30
Q

How does a Rechargeable Battery work?

A
  • During charging, the anode material is oxidized,
    producing electrons, and the cathode is reduced,
    consuming electrons.
  • These electrons constitute the current flow in the external
    circuit
31
Q

What does the electrolyte serve as?

A
  • The electrolyte allows the internal ion flow between the
    electrodes, as in lithium-ion and nickel-cadmium cells,
    and doesn’t allow electrons to flow through
  • It may be an active participant in the electrochemical
    reaction, as in lead-acid cells.
32
Q

What are the different types of chemicals that are combined in different combinations to make rechargeable batteries?

A
  • Lead-acid
  • Nickel-cadmium (NiCad)
  • Nickel-metal hydride (NiMH)
  • Lithium-ion (Li-ion)
  • Lithium-ion polymer (LiPo)
  • Rechargeable alkaline batteries
33
Q

What are Lead-Acid batteries?

A
  • Lead-Acid batteries are the oldest type of rechargeable battery
  • Their ability to supply high-surge currents means that the cells maintain a relatively large power-to-weight ratio
  • These features, along with their low cost, make them attractive for use in motor vehicles, which require high currents
34
Q

What are some types of batteries?

A
  • Nickel-Metal Hydride
  • Lithium-Ion
  • Lithium-Ion Polymer
  • Alkaline Batteries
35
Q

How do Lithium-Ion batteries work?

A
  • Lithium ions move from the negative electrode to the
    positive electrode during discharge, and back when
    charging
  • The negative electrode of a conventional lithium-ion cell is
    made from carbon
  • The positive electrode is a metal oxide, and the
    electrolyte is a lithium salt in an organic solvent
36
Q

Properties of a Lithium-Ion Battery

A
  • Good energy density
  • Slow loss of charge when not in use
  • More expensive than NiCd batteries but operate over a
    wider temperature range while being smaller and lighter
  • They are fragile and thus need a protective circuit to limit
    peak voltages
37
Q

What is a Lithium-Ion Polymer batteries?

A
  • Composed of several identical secondary cells in parallel
    to increase the discharge-current capability
  • They are often available in series “packs” to increase the
    total available voltage
38
Q

What makes Lithium-Ion Polymer batteries different from Lithium-Ion batteries?

A
  • Their primary distinction from lithium-ion batteries is that their lithium salt electrolyte is not held in an organic solvent
  • Instead, it is in a solid polymer composite, such as polyethylene oxide or polyacrylonitrile
39
Q

What are the advantages and disadvantages of Lithium-Ion Polymer batteries?

A

The advantages of LiPo over the lithium-ion design include:
- potentially lower cost of manufacture
- adaptability to a wide variety of packaging shapes,
reliability, and ruggedness

Disadvantage:
- They hold less charge

40
Q

How must the Gearing and Drive Shaft be?

A
  • Wear resistant (hardness)
  • Self lubricating
  • Provide required ratio
  • Frictionless
  • Strong (Strength)
  • Stiff (Young’s modulus)
  • Serviceable
41
Q

How must the Gearing and Drive Shaft be?

A
  • Wear resistant (hardness)
  • Self lubricating
  • Provide required ratio
  • Frictionless
  • Strong (Strength)
  • Stiff (Young’s modulus)
  • Serviceable
42
Q

How must the Gearing and Drive Shaft be?

A
  • Wear resistant (hardness)
  • Self lubricating
  • Provide required ratio
  • Frictionless
  • Strong (Strength)
  • Stiff (Young’s modulus)
  • Serviceable
43
Q

What are some engineering details which are necessary to make the drill work?

A
  • Bearings
  • Bushes
  • Surface finishes
  • Tolerances
  • Keyways
  • Clips and springs
  • Joining

Engineering Applications 3004 (11 decks)

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