College Engineering Aptitude Test Notes

Robotics, Subsystems, and Gear ratio Terms

What Is a Gear Ratio?

The amount of Torque Vs. the Amount of Speed

Torque

Measurements of force that causes and object to rotate around a point (lb/ft)

Speed

The distance traveled per unit of time

Parts of a gear train

Driver: The gear connected to a motor

Idler: The gear that spins in the inverse direction of the driver and does not affect the final gear ratio

Driven Gear: causes either no change, a reduction, or an overdrive

Gear ratio formula

(Teeth of Driver) / (Teeth of driven)

Reduction

When the input driver is smaller (has less teeth than the output driver) and decreases the speed

Overdrive

When the input driver is larger (has more teeth) than the driven gear and increases the speed (Rpm)

How to calculate rpm based on gear ratio

Ratio = 24/12 = 2:1 = 2

Input Speed 1500 RPMs

Output Speed = 1500 x 2 =  3000 RPMs

(If 12:24 RPM would be 750)

How many Robotics Subsystem are there?

6

Structure:

Any physical part of the robot: All metal, fasteners, and structure/mechanical plastic parts

Motion:

Anything that makes the robot move: Motors, Servos, Gears, Chain and Sprockets, Tank Treads, etc.

Sprocket and gear used in Bike pedals: Sprocket is the smaller driven gear with teath

Power:

Batteries, Wires, Pneumatics, chargers

Sensors:

Anything that takes input from the environment

EX: Bumpter, Limit Switches, Ultrasonic, Encoders, Potentiometers, Vision 

Control

Anything that controls/ communicates with the robot

Ex: joystick, Radio, Cables

Logic:

Brain and Programming Part of the robot

EX: RoboRio, microcontroller, PWN cables, and Programming Kits

Mechanical advantage

The process of using machines to overcome work (Force)

Rotational Speed

The frequency of ration of an object around an axis (RPM)

Acceleration

the rate of change of velocity per unit of time. Changes in both speed and direction over a distance *** includes velocity a bit

Force

The push or pull on an object with mass causes it to change its velocity.

Work

the transfer of energy by a force acting on an object as it is displaced.

EX: Carrying a backpack (Force is a must when work is done)

Power

the amount of energy transferred or converted per unit time.

Voltage

electrical potential difference between two points in a circuit, driving the flow of electric charge, measured in volts.

EX: in a battery, the voltage is the difference in potential energy between the positive and negative terminals, and this difference drives the flow of electrons through a connected circuit.

Free Speed

The max RPM that a motor could spin without any interruptions

Free Current

The current (Electrical Output) generated by free speed

Stall Torque

The limit of force a motor can output to lift/Rotate an object

Stall Current

How much current (Electrical output) is generated when the motor stalls

Current Limit

limit put of the motor to not burn out (Overheat) after stall torque is reached — built into most motors

Belt Drive

Two wheels attached to a pully used to move a belt over a distance

Rack and Pinion

Takes rotational movement from a gear and turns it into a liner (Forward and Back) motion

Lead Screw

As the screw turns (rotational) is moves along the lead to create lateral or linear motion.

EX: Sliding up and down a fireman’s pole while spinning.

Worm and Wheel

As the worm wheel (Gear rotates), it causes a rotational spin on the worm (Bar) that is perpendicular to the wheels rotation

Cam and Follower

As the follower (wheel) rolls along the side of the cam (Wedge shape) it allows a movement up and down.

EX: Seen in pistons and car engines

Bevel Gears

Gears 90 degrees to ectotherm and the teeth at 45 degrees to each other and creates an orbiting motion

Seen at the bottom of cars: Rear Differential