Basics of Robotics – Home-Grown Robotics

In this article, I wish to address some of the basic concepts you should know about when starting to participate in an FRC Team, Robotics as a hobby, or just wanting to know more about how robots do anything!

Calculus	Differential Equations	Linear Algebra
Control Systems	Data Collection and Processing	Basic Electrical Engineering

Odometry

In simple terms, Odometry is the use of sensors to track the location of the robot.

Degrees of Freedom (D.O.F)

Sensors:

Encoders

Rotary, Linear

Incremental
Absolute

*Magnetic Encoders can be made as Incremental and Absolute; they just use magnetic fields as the trigger*

Encoder Math Basics:

$c$ is wheel circumference, the distance traveled in one revolution.

$t$ is the current internal time of the robot since the start of the mission.

$t_p$ is the previous time saved since the last encoder reading was captured.

$n$ is the number of encoder ticks per revolution.

$N_c$ is the number of encoder ticks for the wheel $w$ at time $t$ .

$N_p$ is the previous number of encoder ticks at time $t_p$ .

We can implement this data collection with the ticks of the encoder attached to interrupt pins on our processing unit, such that, if we know how far the wheel has moved, the formula for velocity can be applied and we can know how fast the motors are moving and use this feedback to maintain a set velocity and match the wheels together to maintain the motion we want.

$Distance = Circumference * Revolutions$

Encoder resolution can be calculated by knowing the max RPM and encoder operating frequency. Specifying resolution starts with determining the smallest increment that needs to be seen. If we need to measure a minimum of 2°. The number of points $N$ to measure per revolution is given by:

$N = \frac{360^{\circ}}{2^{\circ}}$

$Max~encoder~resolution = \frac{f_{operating}~*~60~Hz}{RPM_{Max}}$

Inertial Measurement Units (IMUs):

The next step in sensor feedback is an inertial measurement unit or I.M.U. This device can be used to measure how much the robot is rotating about a given axis. With this information we can tell if the robot is going straight or not, and with some basic geometry we can tell what sort of arc it is taking when we want it to be turning and control this motion with greater precision.

Chassis and Materials

The Unit Circle

This will help with the mathematics.

Actuators and End Effectors

D.C Motors

A.C Motors

Stepper Motors

Servos

Linear Actuators

Pneumatics

Grippers

P.I.D Control

P: the further you are from where you want to be, the harder you should try to get there.
I: the longer you haven’t been where you want to be, the harder you should try to get there.
D: if you’re quickly getting close to where you want to be, slow down.

Power Supplies

Batteries

A.C Supply

Up Next: Differential Drive