# Using Limits to Control Range of Motion In [Part 2: Robot Control](https://docs.revrobotics.com/duo-control/hello-robot-blocks/part-2/arm-control-blocks/adding-a-limit-switch) 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.

maxPosition and minPosition added for our limits

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 ![](https://1359443677-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FUOOiQ4S2QcMWmVoSmeQ8%2Fuploads%2FhrFxXaL515iousGSa632%2Fimage.png?alt=media\&token=8ad2155b-9bb1-48bd-88d5-0cdc188f22ee) block previously used for [`armPosition`](https://docs.revrobotics.com/duo-control/hello-robot-blocks/part-3/calculating-target-position#adjusting-our-if-else-statement) 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](https://docs.revrobotics.com/duo-control/hello-robot-blocks/part-3/arm-control-with-encoders-blocks/estimating-the-position-of-the-arm). ![If/Else Statement for arm movement](https://1359443677-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4_pJHI8HTuZFQTNfcy%2F-Mb7NRLlN4cP21O7utyz%2F-MbDOTQhQBREe4ZXSqoI%2FArm%20-%20limit%20if%20else%20logic.svg?alt=media\&token=f85b763f-de4a-4031-8774-4e505ebd8547) 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 the `maxPosition`. * If down on the Dpad is pressed and the position of the arm is greater than the `minPosition` then the arm will move towards the `minPosition`.

Use the "logic" dropdown to fill out the statement's check

## 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](https://docs.revrobotics.com/duo-control/hello-robot-blocks/part-1/programming-touch-sensors) from Part 1: Tackling the Basics for review if needed!

Touch sensor limit switch added as a separate If/Else statement

Save your OpMode and try testing it!