ROBOT CONTROL

A simple GUI runs on the PC during the localization process. The GUI gives you some simple options for commanding the Robosapien. For this project, the commands were limited to Stop, Go Forward, Turn Left, and Turn Right. When you select a command, the computer sends a command packet down the serial port to the C node, which broadcasts the command packet over the wireless network. When the R node receives this packet, it executes the command specified on the Robosapien and then broadcasts a packet to signify that it has performed the command. Meanwhile, the T node stops sending information after it receives the command packet so it won’t bog down the network. It then begins its transmissions once it receives the command-executed packet from the R node.

To ensure that the correct command has been executed, both the command and command-executed packets also contain a command number indexed from zero at the beginning of operation. It wraps back to zero when the maximum command number has been reached. Table 1 includes all of the packets and their formats.

The final phase of our project involved executing a command at node R on the Robosapien. After dissecting the Robosapien, we decided that the easiest way to command the robot using a Freescale ZigBee node would be to replace the Robosapien’s infrared receiver with the ZigBee node. The node was programmed to mimic the signals from the Robosapien’s infrared receiver. These signals were discovered experimentally with an oscilloscope. We found that command signals sent to the Robosapien were made up of four distinct time slices: 7, 3.3, 1, and 0.7 ms. When data isn’t transmitted, the logic level for the command signal is high (logic 1).

For example, take a look at the Go Forward command in Figure 3. These signals include only four time slices, so they are easily stored on a Freescale node as an array.

(Click here to enlarge)

Figure 3—We deciphered the Go Forward signal using an oscilloscope.

Take a look at the Go Forward command stored on a node:

int FORWARD_COMMAND[] = {1,2,3,4,3,4,3,

            4,3,4,3,2,3,2,3,4,3,-1};

Each number represents one time slice. The terminating -1 exists because not all commands are the same number of time slices. This format allows for a simple while loop command implementation that uses a delay function to create each time slice. Port C5 on the MC13192 evaluation board was connected to the Robosapien’s IR receive wire in place of the actual IR receive module. We were able to transmit commands from the ZigBee network to the Robosapien by toggling port C5 high and low.