Practical sessions - Electrical drill

Question 1

Main Sub Assemblies of a electrical drill?

Answer 1

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

Question 2

What does the casing do?

Answer 2

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

Question 3

What must the material used for casing be?

Answer 3

• 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)

Question 4

What does the PCB and control do?

Answer 4

• 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

Question 5

What must be included to control the drills operations?

Answer 5

• PCB
• Wires
• Switches
• LEDs
• Connectors
• Meet WEEE regulations

Question 6

What does the Gearing and Drive Shaft do?

Answer 6

• 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

Question 7

How must the Gearing and Drive Shaft be?

Answer 7

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

Question 8

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

Answer 8

• 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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

What does the motor do?

Answer 11

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

Question 12

What must a motor’s properties include?

Answer 12

• 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)

Question 13

How does a Motor work?

Answer 13

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.

Question 14

What are Motor’s powered by?

Answer 14

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

Question 15

What is an electric generator?

Answer 15

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

Question 16

What are the Main Components of an Electric Motor?

Answer 16

• Rotor
• Bearings
• Stator
• Air Gap
• Windings
• Commutator

Question 17

What is a rotor?

Answer 17

• 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

Question 18

What do the Bearings do?

Answer 18

• 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

Question 19

What is a Stator?

Answer 19

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

Question 20

What is the stator made up of?

Answer 20

• 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

Question 21

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

Answer 21

• 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

Question 22

What are Windings?

Answer 22

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

Question 23

What is a commutator?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

What is the rechargeable battery?

Answer 25

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.

Question 26

What must it the rechargeable battery be?

Answer 26

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

Question 27

What is a Rechargeable Battery comprised of?

Answer 27

- 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

Question 28

What do rechargeable batteries consist of?

Answer 28

An anode, a cathode, and an electrolyte

Question 29

Why is demand for rechargeable batteries growing?

Answer 29

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

Question 30

How does a Rechargeable Battery work?

Answer 30

- 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

Question 31

What does the electrolyte serve as?

Answer 31

- 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.

Question 32

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

Answer 32

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

Question 33

What are Lead-Acid batteries?

Answer 33

- 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

Question 34

What are some types of batteries?

Answer 34

- Nickel-Metal Hydride - Lithium-Ion - Lithium-Ion Polymer - Alkaline Batteries

Question 35

How do Lithium-Ion batteries work?

Answer 35

- 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

Question 36

Properties of a Lithium-Ion Battery

Answer 36

- 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

Question 37

What is a Lithium-Ion Polymer batteries?

Answer 37

- 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

Question 38

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

Answer 38

- 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

Question 39

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

Answer 39

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

Question 40

How must the Gearing and Drive Shaft be?

Answer 40

- Wear resistant (hardness) - Self lubricating - Provide required ratio - Frictionless - Strong (Strength) - Stiff (Young’s modulus) - Serviceable

Question 41

How must the Gearing and Drive Shaft be?

Answer 41

- Wear resistant (hardness) - Self lubricating - Provide required ratio - Frictionless - Strong (Strength) - Stiff (Young’s modulus) - Serviceable

Question 42

How must the Gearing and Drive Shaft be?

Answer 42

- Wear resistant (hardness) - Self lubricating - Provide required ratio - Frictionless - Strong (Strength) - Stiff (Young’s modulus) - Serviceable

Question 43

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

Answer 43

- Bearings - Bushes - Surface finishes - Tolerances - Keyways - Clips and springs - Joining