Using Limits to Control Range of Motion
In Part 2: Robot Control the idea of creating a limit switch was introduced using a physical sensor, like a touch sensor. We can make use of our motor's built-in encoder to do something similar. While a physical sensor would be described as a hard limit, using the built-in encoder is called a soft limit.
To set the soft limits we will build off the program created in the last sections (HelloRobot_ArmEncoder)!

Creating minPosition and maxPosition
To start, we need to create our upper and lower limits. Create two new variables one called minPosition
and one called maxPosition
to be added to initialization.

For now we want the minPosition
set as our starting position and the maxPosition
set to our 90 degree position. Set minPosition
equal to and set
maxPosition
equal to . The
block previously used for
armPosition
can be moved to our maxPosition
.

Adjusting our If/Else Statement
To start, our If/Else Statement will be changed back to a simplified format like we had at the beginning of estimating the position of the arm.
To set the limit we need to edit our if/else
statement to include our limits:
If up on the Dpad is pressed and the position of the arm is less than the
maxPosition
, then the arm will move to themaxPosition
.If down on the Dpad is pressed and the position of the arm is greater than the
minPosition
then the arm will move towards theminPosition
.

Overriding Limits
One of the benefits of having a soft limit is being able to exceed that limit.
Remember that the encoders zero tick position is determined by the position of the arm when the Control Hub powers on! So if we aren't careful to reset the arm before powering on our robot this will effect the arm's range of motion. For instance, if we have to reset the Control Hub while the arm is in the 90 degree position, the 90 degree position will become equal to 0 encoder ticks.
As a back up, we can create an override for the range of motion. There are a few different ways an override can be created, but in our case we are going to use the "A" button and touch sensor to help reset our range.
Adding a Gamepad Override
Start by editing the to add another
condition. Use the
block as the condition. Add a
block to the do portion of the
block and set the power to -0.5.

Now that we have this change in place, when the "A" button is pressed the arm will move toward the starting position.
Adding a Touch Sensor Limit
Next, when the arm reaches and presses the touch sensor we want to STOP_AND_RESET_ENCODER
.
We can create an additional statement that focuses on performing this stop and reset when the touch sensor is pressed. Check out Programming Touch Sensors from Part 1: Tackling the Basics for review if needed!

Save your OpMode and try testing it!
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