Comms Link

Thinking more Mars Rover than Robot Wars again, I'm departing from the traditional radio control system. Like the Mars Rover I want to use a bi-directional serial radio link to control the robot and get data back to the control centre. The downside of this approach is that it doesn't result in a dynamic and highly responsive robot, such as that required to compete in competitons like Robot Wars. It also needs some other form of PC or pocket PC to send the required commands over the serial link.

I've got a wired serial link working using pair of ADCON M433MCLight, 19200 baud, radio modems operating at 433 MHz. I've yet to test the full range but it is at least 100m. 8-bits, no parity, 1 control bit.

The comms link is one of the things that can be switched on or off via the I/O board, to save power. Whilst this sounds a bit odd, ultimately the robot will have autonomous control and GPS to guide it and the comms link can draw a reasonable current.

Testing

For testing I'm using a pair of serial cables and a null modem to link another controlling PC to the robot main processor, via the relevant serial ports. I'm currently using hyperterminal to send commands to the robot but I'm going to have to write a controller application if I want to support message sequence numbering and error checking of communications over the data link.

Radio Link

The plan is to simply swap the cable for off-the-shelf radio modules. Some additional power will be needed for the modules though.

Protocol

I still thinking about the protocol over the serial data link. I'm planning to include some form of an acknowledgement from the robot and to include some CRC in the response. I also want to add number sequencing so that the robot can be told to 'undo' moves. Companies Worth looking at:
  • http://www.rfsolutions.co.uk/acatalog/index.html
  • http://www.active-robots.com/products/radio-solutions/rfmodule-details.shtml
  • http://www.radiometrix.co.uk/