[apalrd]

I was trying really hard not to step into any of these threads, but there is some information that needs to be included in this thread, and I feel compelled to post it.


-Everything between the robots and DS's uses UDP/IP which has none of the retransmission problems TCP has. As packets are sent every 20ms and include a CRC, a missed packet will cause a 20ms lag (not bad at all) and it will ignore the packet if the CRC is bad. The FMS also talks UDP to the DS, and the DS talks UDP to the Dashboard. Only the camera uses TCP for the video stream, which is generally unrelated to completely dropped comm (camera problems will show up as lag caused by late packets, and would be seen by a team from the beginning).

-Prior to one of the matches, I opened a WiFi scanner on my phone. The field uses one 5ghz channel for all 6 networks, and nothing else was using 5ghz for 802.11a/n (b/g only run on 2.4ghz). Cellular networks don't run anywhere near 5ghz (they use 700-800mhz, "PCS" 1900mhz, and a funny "AWS" band that splits uplink/downlink on 1700/2100mhz) and are not the cause of interference (if it is wireless interference, which I don't think it is).

-The field-end AP is a Cisco commercial AP, the same one has been used since the control system was introduced in 2009. It's operating exactly in it's intended environment (fixed AP for multiple virtual networks), and any problems with it would show up with all robots.

- The weak link is certainly the D-link AP. Many teams this season have seen random communication loss at their later events. I'm sure a consumer-grade wireless AP designed to sit on a desk or shelf dosen't like being thrown over a bump at 10 ft/sec hundreds of times.

-I believe that any part that is not industrial or automotive grade, or designed specifically for FIRST will not be robust enough for a FRC robot, especially if it is a single point of failure such as the radio.

-I did download FMS light, and the 2011 version of FMS Delta/Full (Full won't run without the PLC, so my play stopped there), and found that it was clearly written in a .NET language and was not terribly stable. I was able to crash FMS Full quite repeatably simply by not having a PLC for it to talk to.

--At an off-season event in 2010, the circuit powering the field tripped a breaker and shut down the FMS server mid-match. Upon reboot, the FTA's found that it would crash when opening because it had entered a date in the MSSQL table that was invalid, and it would not read the tables at all. As the tables were encrypted, the FTA's literally had to guess the password to manually open the tables in MS SQL and fix the date, and found that the password was a string related to FIRST (I don't remember what it was).