Learner
1. What is an encoder? How does it work?
2. There are three main settings for encoders. Briefly explain what each does (which is running at a set speed, which is running at a set power?)
motor.setmode(DcMotor.RunMode.RUN_TO_POSITION);
motor.setmode(DcMotor.RunMode.RUN_USING_ENCODER);
motor.setmode(DcMotor.RunMode.RUN_WITHOUT_ENCODER);
3. Describe the process for setting a motor to turn one full rotation and then stop.
4. Describe the process for setting a motor to run at a consistent speed for two seconds and then stop.
5. This code is supposed to make the motor turn half a rotation. It never moves. There are two errors, what are they? (This is not a configuration problem)
motor = hardwareMap.dcMotor.get("ml");
motor.setMode(DcMotor.RunMode.RUN_WITH_ENCODERS);
startPosition = motor.getCurrentPosition();
waitForStart();
motor.setTargetPosition(startPosition + 500);
Here are the answers.
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1. We have not declared variable a. Line 1 would generate a compiler error.
1a. Declaration creates a variable with it's data type and allocates appropriate memory space based on the data type. A variable must be declared before it's first use. Initialization is assigning a starting value to a newly created variable.
2. Only a single variable can appear left of the assignment ( = ) operator.
3. a = 7, b = 9.
4. a = 7, b = 9, c = 63.
5. a = 7, b = 63, c= 63.
6. a = 63, b = 63, c = 63.
7. a = 63, b = 63, c = 5.
8. The student thinks the definition of c has been permanently changed by line 8 to be b * a. c is a simple integer variable and only contains the numeric value assigned to it. The result of line 8 is c = 63.
9. A compiler error due to the fact we are trying to assign a floating point number to an integer. The Java compiler can't convert the float to an integer without loss of accuracy.
10. The same compiler error for the same reason.
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Given the following statements, answer the questions below:
1) a = 15; 2) int b; 3) b = 12; 4) a = a + 5; 5) b - 2 = 10; 6) int a = b - 5; 7) b = 9; 8) int c = b * a; 9) b = c; 10) a = b; 11) c = 5; 12) c = 3.2; 13) float f = 121.23; 14) c = f;
1. After the code up to line 4 has run, b will indeed be equal to 12, but a will NOT be equal to 20. There actually is an error. What is wrong with what we have done with a up to line 4?
1a. What is the difference between declaration and initialization? (When do you need to say the type of variable, like int)
2. Line 5 also will make java unhappy and won’t do anything (and will actually prevent us from compiling). Why?
3. After line 7, what will the variables a and b have stored in them?
4. After line 8, what will the values of a, b and c be?
5. After line 9, what will the values of a, b and c be?
6. After line 10, what will the values of a, b and c be?
7. After line 11, what will the values of a, b and c be?
8. A student thinks that at the end of line 10, a= 63, b = 63, and c = 3969 (which is 63*63). What mistake are they making?
9. What is the result of line 12?
10. What is the result of line 14.
The answers are on the next page.
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1) a > b;
15.4 greater-than 5.6? True.
2) c > a;
9.8 greater-than 15.4? False.
3) A == a;
Error, variable A not defined.
4) (a > b) || (b < c);
(15.4 greater-than 5.6) or (5.6 less-than 9.8)
true or true ? True.
5) b = 5.1;
Error, not a comparision.
6) b == 5.6;
5.6 equal to 5.6? True.
7) !(c < a)
not (9.8 greater-than 15.4)
not true ? False.
8) (c < a) && (b > a);
(9.8 less-than 15.4) and (5.6 greater-than 15.4)
true and false ? False.
9) !(b != b)
not(5.6 not equal 5.6)
not( false )? True.
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Example of if statement misuse.
Lets say I have a robot that has a servo that I want to control using two buttons on a controller, and I want the following rules to be followed:
-If button A is pressed, the servo extends all the way
-if button B is pressed, the servo extends halfway
-if no button is pressed the servo retracts
Here is a pseudocode implementation of these rules:
if A.isPressed()
servo extends 100%;
if B.isPressed()
servo extends 50%;
else
servo extends 0%;
Consider the case when button A is pressed, but B is not. What will the behavior of this code result in? Fix the code using appropriate changes to the conditionals.
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Given the code below, the desired result is for c to end up as 100 if it’s bigger than b, 0 if it is equal to b, and 5.4 if it is less than b.
1) What does b end up being equal to?
2) According to the rules I wrote in words above, what should c be equal to at the end of this code?
3) Does this code do this?
4) Fix the code to have the desired behavior.
float a = 20;
float b = 5;
float c = 10;
if (a > b)
{
b = 2 * b;
}
else
{
b = 0;
}
if ( c > b)
{
c = 100;
}
if (c == b)
{
c = 0;
}
if (c < b)
{
c = 5.4;
}
Click Next for the answers.
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