Radio

In the FIRST Robotics Competition and the FRC Archive, radio is the primary colloquial term for the various wireless communication systems that robots have employed every year after the inaugural 1992 competition which used wired tethers. Since 2009 this has been accomplished using wifi routers with custom firmware, with older systems using modem radios.

RNet

Motorola RNet radios were the wireless modem radios used for communication in the FIRST Robotics Competition from 1993 to 1999. Rnet radios establish a wireless serial communications link similar to a dial-up modem but over-the-air instead of phone lines.

In the 1990s, teams would be supplied RNets in the kit of parts, but these were collected before the beginning of competition and teams in the pits were required to use a tether cable and tether adaptor, a 9-pin serial cable with a null-modem adaptor inserted to swap over the transmit and receive lines to connect the driver station to the robot controller - this also functioned as a wired tether outside of competition. Teams would be given a radio on the same frequency as the one positioned in their driver station to plug into their robot for the match.

Gallery

• Additional photos on the FRC Archive
• 
  A pair of RNet radios [1]
• 
  The tether cable and adaptor setup [2]
• 
  The transmit side of the 1995 control system with RNet radio [3]

Modem Radios

Starting in 2000 RS-422 modem radios made by Ewave with support for the RM2000 mode that the new IFI control system used were introduced. There are both "Mobile" and "Base" types, with the base having a longer metal antenna and the mobile a black rubbery one, but they can be used on either end interchangeably - as long as there is one of each base and mobile type in the connection pair, not two of the same type. Pairs of radios were given to teams in the kit which would work in conjunction with the robot controller and operator interface's team number settings to link together. At competition, operator-side radios were affixed to the inside of the driver station "glass". Tether cables for robot control were still required in the pits and a serial tether cable had to be used to connect a PC to the robot controller for uploading and debugging code. These radios are classified as 900MHz and operate between 902 and 928MHz with a total of 40 channels, 6 open and 34 competition-only. Because of the way the modems treated two consecutive 0xFF bits as a packet header, the PWM or analogue value of 255 (0xFF) would never be sent from joysticks or on-board sensors with the IFI control system changing the values to 254 before being sent. If two 255s were ever sent in a row, the modem would drop whatever previous bits it was assembling and seek to create a valid packet out of the following data, which would be offset by some amount of bits, creating garbage frames.

IFI offered a pair of Ewave Screamer wireless transceivers to upload and debug code wirelessly.

A larger style of radio was used in 2007 and 2008. These could transmit data at 19200bps compared to the 9600bps connection of the past radio modems.

Documentation

Ewave Radio Modem Technical Manual
Radio Modem Drawings

Gallery

• Additional photos on the FRC Archive
• 
  A "mobile" radio in situ [4]
• 
  Base radios hanging on the driver station wall [5]