Though I haven’t found an explicit mention that it isn’t supported, the REV docs do show that the follower configuration parameters are complicated enough that you shouldn’t set them manually, and the client doesn’t have a way to automatically fill them in. Your best option is probably setting up a control system and configuring the followers in Java or C++. At that point, you may be able to return to using the client, now that the sparks are configured, but I have not tested that.
kFollowerConfig - Special configuration register for setting up to follow on a repeating message (follower mode). CFG[0] to CFG[3] where CFG[0] is the motor output start bit (LSB), CFG[1] is the motor output stop bit (MSB). CFG[0] - CFG[1] determines endianness. CFG[2] bits determine sign mode and inverted, CFG[3] sets a preconfigured controller (0x1A = REV, 0x1B = Talon/Victor style as of 2018 season)
doesn’t seem like getting that working is easier than setting up a RIO.
It is correct that the client does not currently have an easy interface to configure a follower. If you do want to configure it using the client you can use the advanced tab, it is a bit more complex than just setting the CAN ID. It requires the full CAN ID, and some specific configuration.
To set this up, connect to the follower device and set the following settings:
kFollowerID = 33888256 + CANID
CAN ID is the basic CAN ID from 1 - 62. For example, to have device 3 follow device 1, you would set this to 338882567
To have the device follow a SPARK MAX in the same direction set
kFollowerConfig = 436207616
To have the device follow the inverse of a SPARK MAX set
kFollowerConfig = 436469760
Check the configuration carefully and verify the operating direction before running with any kind of load.
In the new Version 1.3.0 of the REV hardware client, you can now much more easily set up a follower mode for multiple motors. Also, you run more than one motor at a time!