I mentor a First Robotics team, and one of our biggest problems is that we have only on c-RIO, and so only one robot can operate at a time. It would be useful to build one or more ‘mules’ that we could test new drive systems, arms, kickers, ball handlers, etc. It would also allow many more students to learn direct programing, not just offering suggestions to the one or two who handle all c-RIO programming, loading, and operating. I have done a bit of Atmega/AtTiny work on custom pcbs, but I do not know about wireless connections. Is it better to use Xbee (ZigBee) to send commands from the computer to the robot (probably an Arduino plus shields plus maybe custom boards) and then send data back? Or would it be better to use an Ethernet shield and put a wireless ethernet router on the robot (plenty of room, and exactly how it is done in FRC) plus a second one connected to the laptop?
Part of the question is also a complete list of hardware and software to make the link. I know how to run RS232 (485) down a Cat5 cable, but how many Xbees does it take to go from laptop to arduino, then from arduino back to laptop? Is there a special Xbee USB dongle for the laptop and then just an Xbee shield for the arduino? Does it take a pair for each direction? How difficult is it to format data/commands from a C program running on the laptop to Xbee signals then convert to something the Arduino can read? And for the return trip. If using wireless ethernet, the laptop to WAP is trivial, but how do you get the data/commands from the WAP aboard the robot through the ethernet shield and into something the Arduino can read? At least for this ‘tool chain’, the return trip is trivial, and there is enough bandwidth to even consider adding an IP video camera.
I would like to buy all the parts and test this out before teaching the kids, but I don’t know what parts to get. I assume after putting all the parts together, there will be code snippets or app notes to complete the software side of the interface?
Mike
See this [tutorial on XBee modules, from the [Parallax site. After reading the tutorial you’ll probably decide that in a closed environment that the low power, Series 1 are suited to your needs.
You’ll generally communicate with XBees using TTL RS232. Sparkfun sells the XBee Explorer USB (http://www.sparkfun.com/products/8687) which handles everything on the computer side. On the robot/node side you’ll typically want to get a small carrier board (http://www.sparkfun.com/products/9132) or an Arduino with the carrier built-in like the [Seeeduino Stalker. You can control the robot directly from the XBee’s digital and analog pins or interface between the XBee and a microcontroller (Arduino) on the robot using the XBee’s serial interface.](http://www.seeedstudio.com/depot/seeeduino-stalker-v2b-p-727.html)](http://www.parallax.com/tabid/829/Default.aspx)](http://www.parallax.com/portals/0/downloads/docs/prod/book/122-32450-XBeeTutorial-v1.0.pdf)
Thanks for the quick reply. I had searched a dozen prior threads, but all seemed to be focused on one small section of the link, not what to buy to get started. Later, I found the Sparkfun XBee USB explorer and XBee USB dongle, but it was unclear whether I needed to buy an Xbee transceiver in addition to that just to get the laptop side going. Then I found the XBee Wireless KIT (at Amazon), and it became clear that I needed two boards (one USB cable attached to computer or computer dongle and the other an Arduino shield for the robot)and two Xbee transceivers to make the connection I wanted. I will read the tutorial later, and see if that answers enough questions that I don’t also have to buy the building wireless sensor networks book.
I was initially wondering if the 1mW Series 1 transceivers that are bundled into the kit would have enough range. The specs here on Sparkfun are 300 ft/100m which should be plenty for LOS robot control. I also see lots of recommendations in the Series 2, higher powered parts that the ability to make mesh networks with them makes them much more complicated for point-to-point robot control like I am planning. So it looks like the package has the right ones to begin with.
Mike
For robots, I recommend Series 1 XBee PRO, the higher power units. These give you more fade margin.
I don’t recommend Series 2 as these are ZigBee which is a complicated overkill if you don’t need mesh networking (repeaters).