In the previous section you learned how to set the motor to run at a specific power level in a specific direction. However, in most applications, it will be necessary to control the motor with a gamepad, to easily change the direction or power level of a mechanism.
We are able to use a button to set the motor to a specific power or we can program it so it changes based on the direction of one of the gamepad's joysticks!
Using our existing test_motor.setPower(1); we can replace the value of 1 with this.gamepad1.left_stick_y;
Now the power of our motor will be set in response to the position of the gamepad's left joystick as it along the y-axis!
Build your OpMode and test it out with your gamepad! Think about the following questions while testing:
What happens when you move the left joystick up a small amount versus a large amount?
What happens if you move the joystick to the left or right along the X-axis?
What happens if you move the joystick at a diagonal or rotate it 360 degrees?
You may notice that when moving along the X-axis nothing happens at the moment. However, once the joystick hits an angle near the Y-axis vertices the motor may start to jitter and spin.
When you tested your program, did the motor spin the expected direction while moving the joystick up or down?
In the FTC SDK for most controllers the Y value of a joystick ranges from -1 when a joystick is in its topmost position, to +1 when a joystick is in its bottommost position.
That may be a little confusing to control, but we can add a negative symbol, or negation operator, to the line of code to change the direction of the motor in relation to the gamepad.
Recall that telemetry is the process of collecting and transmitting data. There is a lot of useful information our motors could send back to us, but to start let's have it output the power based on the joystick's movement.
Similar to our servo program, let's add a new line of telemetry.addData();.
This time we are going to set our string as "Motor Power" and after our comma will use test_motor.getPower()
Let's start by getting a motor spinning by adding the line test_motor.setPower(1);
Select Build Everything to build the code.
Try running this OpMode on the test bed and consider the following questions:
How fast is the motor running?
What happens if you change the power from 1 to 5? What about 100?
What happens if you change the power from 1 to 0.3?
This is a good time to experiment with different values to see how our motor reacts. You might notice that setting our power to 5 or even 100 does not make the motor spin any fast than when set to 1. But setting our power to 0.3 significantly slows our motor's speed, right?
Now what happens if you change the power from 1 to -1?
From our perspective, a power level of 1 probably doesn't sound very strong. However, to our robot the power being set to 1 translates to the motor running at 100%. That would mean setting the power to 0.3 requests the motor to spin at 30% of power.
When we set our power to a negative power, the motor is told to reverse direction while maintaining that power. So if we set our power to -1 then our motor will still run at 100%, but in the opposite direction than when set to 1.
The direction a motor spins may be determined by the power OR may be designated during the initialization process.
Modify your OpMode to add the motor related code. For now your completed servo code can be dragged to the side of your work space. You may alternatively choose to create a second program.
Just like servos, a motor is a form of actuator. You may picture a dozen different things when you think of a motor, from those used to spin the wheels of a car to the large turbines that allow a plane to fly. For our robots, we will be focusing on DC motors. These are a type of electrical motor that use direct current, or DC, to rotate and produce the mechanical force needed to move an attached mechanism.
For this tutorial, either a Core Hex Motor or HD Hex Motor may be used as long as they have been properly configured on the Driver Hub.
Most standard motors are able to continuously rotate in either direction with an adjustable speed or power. Some motors may also include a built in encoder, which allows them to move to a specified position, similar to a servo, or to collect data like the number of completed rotations!
In the next few sections, we will be learning to program our motor to first move automatically in different directions then in response to our gamepad inputs. In our final section we will take a look at using telemetry with our motor's built in encoder.
Below is a sneak peek of our full code: