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Tech Challenge CSA Troubleshooting Manual
Revision 1: 01.19.24
Distributing Robots Across Multiple Channels
Wi-Fi Channel Overlap
If there is an event that will have a large number of robots (> 40) in a small area, you should consider
distributing the Robots across multiple channels. Ideally, the lower the number of robots there are per channel,
the less traffic and interference there will be per channel. Note that 2.4 GHz Wi-Fi channels that are less than 5
channel widths apart overlap (see Figure 22).
Ideally, for 2.4 GHz Wi-Fi connections, you should distribute your robots on channels that are at least 5
channel widths apart. For example, if you were to configure one group of robots to channel 1 and a second
group to channel 5, the two groups of robots would overlap slightly since the second channel is only 4 channel
widths away from the first channel. If the second group of robots were moved from channel 5 to channel 6,
then the two groups would no longer overlap since they are 5 channel widths apart.
Sometimes it might not be possible to space your robots 5 channel widths or greater apart. For example, one
portion of the spectrum might be very noisy, and the robots are unable to operate on channels in or near that
portion of the spectrum. In this case, it still might be beneficial to place the robots in groups on separate,
overlapping channels. Even though the channels overlap slightly, placing the robots onto these channels might
produce lower ping times and more responsive robots when compared to keeping all the robots on the same
channel.
Factors to Consider when Selecting Wi-Fi Channels
If you would like to configure your robots to operate on more than one channel, here are some factors to
consider when doing your planning:
1. How many robots will be present? The data rates for the control streams of the robot are low. If the
wireless environment at your venue is clean, then a single channel should be able to support a pretty
large number of robots. In our testing, we could run 46 pairs of Android devices in a very tight area
(approximately 14’ x 14’) with good reliability and responsiveness.
If your event will have a modest number of robots (less than 40), and if your wireless environment is
clean, then you probably do not need to worry about moving robots around to different channels.
If you do have a large group of robots, then you should consider dividing them up, so you have a
maximum of 35 to 40 groups per channel if possible. For example, if you have 70 robots, you can divide
them into two groups of 35. You can also break up a large number of robots into even smaller groups
and then place them onto multiple, overlapping channels if needed.
2. Before you select your channels, are the target channels clear? Before you move your robots to a
specific channel, you should do some tests on the channel to verify that it is clear.
a. Use Wi-Fi Analyzer or a similar tool: You can use a tool like Wi-Fi Analyzer to see how many
access points are present on a channel. Remember, Wi-Fi Analyzer only shows you the visible
(non-hidden) wireless network. Also, Wi-Fi Analyzer does not show you how busy a channel is,
it only shows you what visible Wi-Fi networks are on a channel.
b. Use a pair of Android devices to monitor ping times: If a target channel looks relatively
clean, you should use a pair of Android devices running the FTC Driver Station and FTC Robot
Controller apps to monitor the ping times on the target channel. You will need a pair of Android
devices that support channel changing (such as approved FTC phones). You should switch to
the target channel and test to make sure you can select and run an OpMode (like the NullOp
sample OpMode). If the average ping times for the test Android devices are low (< 5 msec) then