1. Auto Straightening using VEX Shaft Encoders

2. Learning Objectives
Understand how the strategy for using shaft encoders to help the robot drive straight.
Be able to program the robot to go straight using shaft encoders
Be able to use the while loop, if and variables.

3. Using Encoders to go Straight
Limit drifting when trying to go straight
In this section we will look at if
else
Variables and types
Applying all of this to help the robot go straight

4. Flowchart for the day
Take notes on a video using the motor encoders to go straight.
Discuss the video and focus on using the if statement with encoders to get the robot to go straight.
Online time to test the code on the ‘Huge Table’
Take notes on videos on using variables to help refine the motion
Discuss the video
Incorporate variables into your sample program.
Start the next set of Challenges
Cortex Videos 1 and 2.

5. Pseudo Code (What we are trying to get the robot to do)
While the robot has not reached the destination
If the left motor has gone farther, slow the left motor and have right motor go at speed
If the right motor has gone farther, slow the right motor and have the left motor go at speed
If the motors are the same, have both motors go at speed

6. If Statements
When your robot reaches an if Statement in the program, it evaluates the condition contained between the parenthesis.
If the condition is true, any commands between the braces are run.
If the condition is false, those same commands are ignored.
Very similar to how a while loop works, but does not repeat the code!

7. Going Straight: Translating to Code
Pseudo Code While the robot has not reached the destination If the left motor has gone farther, slow the left motor and have right motor go at speed If the right motor has gone farther, slow the right motor and have the left motor go at speed If the motors are the same, have both motors go at speed

8. If-else statements
The if-else Statement is an expansion of the basic if Statement.
The “if” section still checks the condition and runs the appropriate commands when it evaluates to true
Using the “else” allows for specific code to be run only when the condition is false.
Either the “if” or the “else” branch is always run; no more, no less.

9. Implementing if..else Code this and test it on the Huge Table.
Take notes on Videos 3 and 4.

10. But…
If the motors are not close in their Power to Speed then the difference between 50 and 63 might not be sufficient.
So it will take some tweaking.
Rather than changing the 63 to another value when modifying the ‘at speed’ needed, you can use variables.

11. Make sure these are in your notes.
RobotC Variables
Make sure these are in your notes.
int
Stores integer values: 5, 0, -100
float
Stores floating point (real) values: 3.01, -5.21, 0
string
Stores words: “Hello World”
char
Stores single characters: “A”,
bool
Stores Boolean (true, false) values

12. Code After Using Variables for Speed Values
Declaring the variables.
type name;
Modify your going straight code to incorporate variables.
Initialize the variables.
Try modifying the fullSpeed and slowerSpeed values to see how if changes the robot behavior.

13. Summary motor[] SensorValue[] wait1Msec() while if if..else Conditions
Conjunctions
Motors and Sensor
Quadrature Encoder
Strategies on going straight
Timing vs. distance

14. Driving Straight Activity
Use the Clawbot
Next set of challenges
Driving Straight II using encoders
Bull in the Ring: Using a while or an if
Robo-Slalom I: Using a while or an if