Introduction to Vexnet

VEX net Joystick  Although many robots are designed to operate autonomously, there are often situations where manual control of a robot is necessary. The VEXnet Joystick allows a human operator to control a robot in real-time using the innovative VEXnet Wireless link. The human operator sends commands to the robot by interacting with the buttons and joysticks on the VEXnet Joystick. These commands are sent to the Cortex Microcontroller via VEXnet signals through a VEXnet USB Adapter Key to one attached to a microcontrolleron a VEX robot. The joystick has two 2-axis analog joysticks, four trigger buttons and two 4-button directional pads. It also has an accelerometer that provides X-Y tilt outputs. This allows you to control an arm or drive system by changing the orientation of the joystick (tilting).

VEX net Joystick

VEX net Wireless Link The VEX Cortex Microcontroller uses a wireless link for communications through a proprietary VEXnet implementation. This implementation is designed to eliminate the need for any knowledge of IP addresses, MAC addresses, security settings, and IP protocols. Just turn it on and it automatically connects to the correct Joystick. The VEXnet implementation utilizes wireless communication within the 2.4 GHz frequency band. Using this type of wireless communication allows huge amounts of data to be instantly transmitted back and forth between a VEXnet Joystick and a VEX Cortex Microcontroller. In the past, the only way to securely and reliably transmit such a large volume of data was by the use of wires and cables. However, this would not be conducive in many robotic applications. VEXnet allows users to gain complete and instantaneous wireless control. Setting up the VEXnet Wireless Link Refer to the Cortex Microcontroller and VEXnet Joystick User Guide to setup the VEXnet Wireless Link. This document is a very valuable resource when working with any VEX robot. Make sure to read it thoroughly and keep a copy handy. It includes many troubleshooting tips. Pair VEX Cortex Microcontroller and VEXnet Joystick. This procedure is detailed in Step 1 of the User Guide. 

Plugging In and Controlling Motors The VEX Clawbot has four motors which power the two sides of the drivetrain, claw motor and arm motor. How does the VEXnet Joystick send commands to these specific motors? Earlier in this unit, the VEXnet wireless link was discussed, which allows users to send commands to microcontroller. There was also discussion of the preloaded default code, loaded onto the microcontroller, which allows users to quickly get their robots running. This default code is programmed to map the controls on the VEXnet Joystick, directly to the motor ports on the Cortex Microcontroller. When the following motors are plugged into the following ports, the default code allows for the following controls.

Motor Motor Port VEXnet Joystick Control Left Drive Motor 1 Left Joystick Claw Motor 6 Left Shoulder Buttons Arm Motor 7 Right Shoulder Buttons Right Drive Motor 10 Right Joystick

Plug the left drive motor directly into motor port 1 on the Cortex Microcontroller. Make sure the red wire is on the left side. Plug the right drive motor directly into motor port 10 on the Cortex Microcontroller. Make sure the red wire is on the left side. Plug the claw motor into a motor controller 29, making sure that the colors of the wires match up. Plug the other end of the motor controller 29 into the Cortex Microcontroller. This is a keyed connection, so there is only one way to plug this wire in. Plug the arm motor into a motor controller 29, making sure that the colors of the wires match up. Plug the other end of the motor controller 29 into the Cortex Microcontroller. This is a keyed connection, so there is only one way to plug this wire in. For more details on wiring the VEX Clawbot see page 16 of the Clawbot Assembly Instructions.

Installing Batteries and VEXnet Keys Plug a 7.2v VEX battery into the 7.2v battery port on the front of the Cortex Microcontroller, next to the on/off switch. This is a keyed connection, so there is only one way to plug this wire in. Plug a VEXnet key to the Cortex Microcontroller into the USB slot on the top of the Cortex Microcontroller. Using a Phillips head screw driver or VEX 3/32 Allen Wrench (depending on which version of the Joystick is used), remove the screws that attach the battery cover to the VEXnet Joystick. Remove the battery cover. Install six (6) identical AAA batteries into the VEXnet Joystick. DO NOT mix different types of batteries. Reinstall the battery cover by inserting the two tabs of the battery cover along the back edge to aid in installation, and then reattach the screws that were removed earlier. Plug a VEXnet key to the VEXnet Joystick into the USB slot above the battery cover.

Getting Started Now that the Robot is completely wired and ready to go, it’s time to take it for a test drive! The above chart explains the control configuration for the Clawbot. The Clawbot by default is set to operate in “Tank Drive” mode. This means the left and right wheels are controlled separately by individual joysticks; this is the same way a tank is controlled. To make the robot go forward, push up on both joysticks. To make the robot go backwards, push down on both joysticks. To make the robot turn left, push the right stick up and the left stick down. To make the robot turn right, push the left stick up and the right stick down. Experiment with different combinations to achieve various “arc” patterns while driving.