FIRST Robotics Competition Documents
As we all get our drive systems working, we are moving on to connect our auxiliary devices, such as motors and solenoids. With this, we will generally use joystick buttons to control these devices. To get started with this, we'll go through several ways to control devices with joystick buttons.
Setup:
No matter what the configuration, you'll need to add one, two, or more (if you're really excited) joysticks to the "Begin.vi". The first example uses 2 joysticks and the others only use one joystick. Give each joystick a unique name, so we can use it in multiple places, an example of this is shown in the snippet below. I named mine "LeftStick" and "RightStick" because they are on the left and right sides of my desk. If your joysticks are already configured, great! You can skip this step.
The rest of the code in this document will be placed in the "Teleop.vi" Here, we will program our joystick buttons to control different aspects of our motors or solenoids.
Scenario 1: I want a motor to move one way when I press one button and the other way when I press a different button.
This code uses button 0 on two different joysticks to control the same motor. If button 0 on LeftStick is pressed, the motor moves backward and if button 0 on RightStick is pressed, the motor moves forward. If both buttons are pressed or not pressed, the motor doesn't move. Here, I named my motor reference "Motor5", but you can name your motor whatever you want in the "Begin.vi".
You may want to use multiple buttons on the same joystick to control the motor, an example of this is shown in the following VI snippet or the VI snippet in Scenario 2. Here, I used buttons 0 and 2 on the LeftStick joystick, but feel free to use whatever buttons you need.
Scenario 2: I want different joystick buttons to move at various speeds.
This example could be helpful if you need to have one motor do different things, based on the buttons you press. For instance, let's say my joystick has a trigger (button 0) and 4 buttons on top (buttons 1 through 4). In this case, the following buttons should have the following functions:
- button 1 - move backward at half speed
- button 2 - move forward at half speed
- button 3 - move backward at 1/4 speed
- button 4 - move forward at 1/4 speed
- trigger - full speed ahead! (forward at full speed)
We would then take the Boolean array from the "JoystickGetValues.vi" and wire it to a "Boolean Array to Number" node (Numeric Palette->Conversion Palette). This converts the Boolean array to a number that we can use. Wire this numeric to a case structure.
Each case corresponds to a binary representation of the values in the array. In this example, each case corresponds to a one-button combination. We added six cases: 0 (all buttons off), 1 (button 0 on), 2 (button 1 on), 4 (button 2 on), 8 (button 3 on), and 16 (button 4 on). Notice we skipped value 3, because this would correspond to buttons 0 and 1 pressed at the same time. We did not define this in our requirements, so we'll let the default case handle it.
Since our requirements were simple, we only need a single constant in each case. For case 1 (full ahead) we use a 1, for case 2 (half back) we use a -0.5, for case 4 (half forward) we use 0.5, for case 8 (1/4 back) we use -0.25, for case 16 (1/4 forward) we use 0.25. We can use any constant value between 1 and -1. I left case 0 as the default so if multiple buttons are pressed (any undefined state was reached) the motor will stop. You of course are free to customize these states however you want.
It might be helpful to review the LabVIEW Case Structure Help document.
Scenario 3: I want to control a solenoid with my joystick buttons.
By now, we are familiar with how the joystick outputs the buttons in an array of Booleans. We need to index this array to get the button we are interested in and wire this Boolean to a selected node. Since the "Solenoid Set.vi" requires an Enum as an input, the easiest way to get the Enum is to right click the "Value" input of the "Solenoid Set.vi" and select "Create Constant". Duplicate this constant and wire one copy to the True terminal and one to the False terminal of the select node. Then wire the output of the select node to the "Value" input of the solenoid VI.
Hope this helps! Feel free to comment below.
Happy Roboting!
