[Al Skierkiewicz]

Dale,
The six pin connectors are the only way to go here. The RJ-11's will move slightly in the connector body of the Jaguar and lift one or more of the spring wire contacts. If you examine the connector you will see a slight rise of plastic between each contact on the plug. If the wire doesn't sit down between the two adjacent plastic bumps, the wires move and either touch each other or don't contact the receptacle wires. I don't know why the sheet and FAQ recommend the 4 wire connectors other than those are easily available parts. In most cases if the plug is inserted properly, there is no problem. With a moving robot, and insertions in a confined space, the chance of accurately inserting the plug is vastly reduced.

The terminators in this kind of arrangement add some noise immunity while maintaining the transmission line characteristics of the daisy chain in both directions. If a star configuration were used, it would need to use active drivers each feeding a separate leg of the star. A simple star arrangement with a terminator on each leg without the active drivers would pull the buss impedance so low that the individual drivers would not be able to supply enough current to communicate via the buss. If you check the Jaguar schematic you will find the CAN sense input which is simply a voltage divider feeding the controller. If the voltage at this point falls to a level too low to communicate the controller will simply communicate with the CAN buss.

Just to remind everyone, UTP stands for Unshielded, Twisted Pair and that a four wire UTP has two twisted pairs, a six wire has three twisted pair and a four wire, Ethernet, has four twisted pairs. Each pair acts as a balanced transmission line and in the case of CAT 5 and 6 cables the pairs are twisted at different rates (twists per inch).