27 MHz has 6 sub-frequencies. There are two standard ways to refer to these sub-frequencies: either by their frequency number or by their channel number. The subfrequencies for 27 MHz are Channel 1 (26.995 MHz), Channel 2 (27.045 MHz), Channel 3 (27.095 MHz), Channel 4 (27.145 MHz), Channel 5 (27.195 MHz), and Channel 6 (27.255 MHz).

49 MHz has 5 sub-frequencies: Channel 1 (49.830), Channel 2 (49.845), Channel 3 (49.860), Channel 4 (49.875), and Channel 5 (49.890)

75 MHz has 30 sub-frequencies: from Channel 61 - Channel 90, with frequencies that start at 75.41 for Channel 61 and rise by .02 MHz until you reach Channel 90, which is 75.99 MHz.

The number of channels available for 2.4 GHz depends on the manufacturer of the transmitter and receiver. Spektrum and other DSSS or DSM models divide the 2.4 GHz frequency into 80 channels. Other manufacturers may divide the frequency into more or fewer channels. The advantage of the 2.4 GHz frequency is that no crystals are required to change the channel - the transmitter searches for an unused frequency and locks the receiver to that frequency (2.4 GHz transmitters and receivers must be paired together to work correctly. A transmitter cannot connect with a receiver unless it has been paired with it.) The disadvantage is either cost or time: transmitters and receivers designed to control R/C cars using the 2.4 GHz frequency can be expensive ($500 or more). If you wish to use a transmitter and receiver that is not specifically designed for controlling an R/C car (for example a bluetooth device, transmitting from either a computer or a cell phone), then you will need to program the receiver to operate your bot based on the signals it receives from the transmitter.

Sumo Bots are required to be designed so they can be operated on three different frequencies. This can be three sub-frequencies of one frequency (for example, 27 MHz, channels 1, 3, and 5) or a combination of different major frequencies (example: 49 MHz, Channel 2 and 75 MHz, Channels 63 and 72). As long as you can change the frequency your bot operates under among three different frequencies (or sub-frequencies), you have met the rules. If you are using the 2.4 GHz frequency, then your bot will automatically switch to an unused frequency, so there is no need to worry about the three frequency requirement. However, you need to be aware that if your transmitter cannot find an available channel (for example, if 80 people in the crowd have bluetooth enabled cell phones turned on) then it simply will not transmit until a channel becomes available.

Remote control Transmitter/Receiver pairs that can operate on more than one frequency come with one crystal installed (the crystal is a chip that determines which frequency (or channel) the transmitter is sending out and the receiver is accepting). In the 27 MHz and 49 MHz range, additional crystals are sold in pairs (one for the transmitter and one for the receiver) at $8.00 per pair. In the 75 MHz range, pairs of crytals cost $16.00.

Please keep in mind that some of the cheaper r/c models available that operate on more than one frequency utilize a non-standard method of designating their frequencies (ie: 27 MHz, Channel A and Channel B). To insure that there is no interference between robots, the event supervisor MUST know what frequency your robot can operate on, and MUST be able to tell you to switch to a frequency that he/she knows is not being used by anyone else. It is not the Event Supervisor's job to determine what frequencies are represented by non-standard designations - it is the responsibility of the team. If students cannot tell the Event Supervisor what frequencies their robot uses (in standard format), they will not be allowed to compete in the tournament.

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