Interview Questions, Tesla Questions

Three laws of thermodynamics

0: transitive 1: conservation 2: heat flow 3: absolute zero

What is a 1/4" - 20 x 2" 304 Stainless Steel Phillips Screw

20 threads/inch, 1/4" diameter, 2 inches long, 304 strong common good corrosion resistance, + on screw head

Adding 3 3V batteries in parallel causes

3V, greater mAh

Watt hours in lead-acid, NiMH, and lithium-ion battery

40 lead-acid, ~100 NiMH, 180 Li-Ion Wh/kg

Adding 3 3V battteries in series causes

9V

How to test if battery is still good

Add a load to it, too much of a voltage drop = bad

Compression ductile vs brittle materials

Ductile compression is about equal to its strength under tension, but brittle materials are stronger in compression than tension

Strain equation

E = (L-Lo) / Lo

Flexural Rigidity

EI

True vs engineering and why

Engineering drops in necking, deformed area is less over time, changing stress, but engineering model is a good estimate

Torque equation

F*L

Stress equation

F/A

I2C vs SPI

I2C multi mater half duplex two wire SPI single master full duplex four wire

Input power equation motor

IV

Parallel Axis Theorem

Ix = Ixc + Ad^2

Area moment of inertia rectangular cross-section

Ix = bh^3/12, Iy = b^3h/12

LDO vs Buck Convertor

LDO low noise, for small output current, resistive; Buck can be high noise, heat in MOSFET, efficiency above 85%, reactive

LiOn vs LiPo

LiOn light, large energy density, easily rechargable, requires protection circuit; LiPo less charge easy form

Describe lead acid vs lithium ion

LiOn shorter to charge, higher energy density, smaller profile, overall less costly

Conductivity of materials equation

Lower conductivity comes from higher resistance R = PL/A

Why is the I axis used so commonly in construction

Material furthest from bending axis = larger moment area of moment will be = less deflection there will be based off of PxL/ExI

What courses have you taken ?

Math Taken past Linear Algebra; Physics taken Kinematics, Electricity, Thermal, Magnetism, and Mechanics; CS taken Computing with Python for Scientists and Engineers; EE taking EE fundamentals covering up to Quantum Computation; ME taken ME fundamentals covering tolerances; Structural design, material selection; rapid prototyping; DC motors; Design methodology. Next classes will be Engineering Design, Thermodynamics

Output power equation motor

P = F*v = Tw

Current and Resistance and Power Equation

P = VI = I^2R = V^2/R

deflection of a beam equation

P*L / E*I (Load)∗(Length)/(Youngs)∗(AreaMomentofInertia)

Name layers of battery

PVC wrapper, main steel casing protection, materials for chemical reaction create speciic level of voltage and current (cathode manganese oxide, porous fibrous barrier barrier cathode anode, microscopic holes allow ion atom to pass through), alkaline elctrolyte (Potassium hydrate) soaked into fibrous material, anode zinc powder + gelling agent, sealed with nylon plastic cap, negative terminal steel T cap pushed inside

Shear force

Pulling in two directions

Resistance equation (resisitivvity)

R = P*L/A (resistivity + length / area)

Temperature and Resistance Equation

R = Ro [ 1+ alpha*(T - To)]

power equation motor

ToWo/4

Toughness in graph + explanation

ability to absorb energy, area under the graph

Resistance to bending is called

area moment of inertia

Resilience in graph + explanation

area under elastic region + absorb energy when deforming elastically

How to calculate shear

average shear stress over entire cross section

How do electrically charged motors work

battery moves current between two conductors, creating magnetic field and moving beam

Brittle vs. Ductile

brittle short graph sharp stress crack, ductile long graph able to deform plastically more blunt localized stress crack

Brushed vs brushless motors

brushes commutate motor to cause it to spin. Commutator are sliding contacts that keep contact as they rotate but flip every 180 so flux remains positive. good and cheap, lower efficiency and reliability because of friction, strong source of electromagnetic interference Brushless motors replace the mechanical commutation function with electronic control. high efficiency and reliability, good speed control, more expensive and complex

Servo motor

can actually hold that position instead of constantly running + burning out motor

bus bar in battery packs

can connect batteries in battery pack

Battery life equation

capacity (mAh) / Circuit current (mA)

WHich is cathode which is anode

cathode + sticks out anode - sticks in

Thermal expansion equation

change L = Lo x alpha x change in temperature

How do lithium ion batteries work

charging: Li-Ions anode to cathode; discharge: Li-Ions cathode to anode, electrons go through the same way but through the wire

How do batteries store energy

chemical

Types of beam forces

concentrated, distributed, concentrated moment

Motor controllers purpose

control by asking for speed or positional control, contains encoder

Temperature coefficient of these common materials ranked least to greatest: carbon aluminum steel copper silicon

copper, aluminum, steel, carbon, silicon (negative)

What is a bus bar made of

copper, brass, aluminum

DC vs AC

direct vs alternating (sinusoidal, in and out, outlet)

For semiconductors, as you increase the temperature, resistivity goes... (explain why)

down, negative temperature coeff, unlike metals, contain free electrons and "holes". as temperature increases, # free electrons and holes increase, jumping to higher energy levels and decreasing resistance

In series, current is ___ to each other

equal

Flexural formula

for simple beam bending, internal bending moment * perpendicular distance from neutral axis / moment of inertia about neutral axis

Brittle material examples

graphite, bismuth, bone, cast iron, ceramic, chalk, concrete

highest to lowest ultimate tensile strength graph: copper, polypropylene, aluminum, alloy steel, heat treated alloy steel, cast iron, carbon steel

heat treated alloy steel, alloy steel, carbon steel, cast iron, al, cu, polypropylene

Semiconductors conduct better at a ________ temperature (explain)

higher, lower resistance, alpha/ temperature coefficient is positive so increasing temperature decreases resistance

mAh rating means

how long battery lasts

Internal normal forces

internal force, axis of beam

Internal shear forces

internal force, vertical

Ductility in graph + explanation

length of curve x axis, measure of material to deform plastically before fracture

Gear ratio greater than 1 produces __ in speed and __ in torque

loss in speed and gain in torque

Positive bending moments put the ____ in tension

lower part of the beam

Metals conduct better at a _______ temperature (explain)

lower, lower resistance, alpha/ temperature coefficient is positive so increasing temperature increases resistance

UTS

max stress during tensile stress before fracture

What is chemical energy in a battery turn to

mechanical

What is a bus bar

metallic strip or bar to connect high voltage equipment or low voltage equipment in battery banks for sufficient cooling of conductors

Stepper motor

moves small increments

Bending moments that cause hogging are ____

negative

Types of Supports in Shear + Moment questions

pinned prevent v and h but allow rotation, roller only hor and rotational, fixed all supports

Yield Strength

point at which deforms after

Bending moments that cause sagging are _____

positive

Electromagnetism definition

process by which magnetic field is created by introducing current in the conductor

What are advantages and disadvantages of using a belt?

pros high efficiency and transmit force over longer distance, cons stretch and wear, slip, lower forces due to material properties

Motor drivers

provide power amplification for motors

RC

radio remote controller

Calculating shear using moment of inertia

shear force * moment of area/ (area moment of inertia * section width)

Types of semiconductors

silicon, germanium, and gallium arsenide

Explain dM/dx = V

slope of bending moment = shear force

Explain dV/dx = -w

slope of shear force= - distributed force

briefly explain how batteries work

small chemical reaction (oxidation + reduction) causes buildup of electrons at negative terminal, in a circuit flows from negative terminal, negative combines and releases hydroxide, interacts with zinc, electrons in water released

How does pitch affect strength of a screw

smaller pitch = stronger, can take greater load

Area moment of inertia how to calculate

splitting into small sections, Ix = integrate y^2 or x^2, x y being distance from bending axis.

Name alloys for steel, titanium, aluminum, solder, bronze

steel: carbon, iron, 304 (chromium, nickel) // titanium: dioxide, aluminum, vanadium // aluminum: copper, magnesium, manganese, silicon, tin, nickel, zinc // solder in tin and lead // bronze : copper selenium

The further from a bending axis, the _______ a cross section tends to be (more less stiff?)

stiffer

What's the difference between stiffness and strength?

strength UTS stiff young's modulus/deflection

Right hand rule

thumb: motion, pointer: magnetic field, middle: current

Thermal expansion coefficient of these common materials ranked least to greatest: aluminum, steel, titanium, copper

titanium, copper, steel, aluminum

Describe internal forces of a sagging beam

top compressive, tensile bottom (normal), creates moment and shear forces

What is stall torque and no load speed

torque when there's no speed (stalled), speed when there's no torque (load applied)

For metals, as you increase the temperature, resistivity goes... (explain why)

up, positive temperature coeff: as electrons collide, more resistance and hence greater resistivity

Gear ratio equation

w1/w2 = n1/n2 = d2/d1 = T2/T1, w is angular velocity, n is RPM, d is diameter, T is number of teeth