Can the robot be detached and tethered to a mechanism. For example in 2015, Recycle Rush, Robowranglers had a detached part and it was still tethered to the robot. Is there any rule that prevents the use of tethering a mechanism, in regards of the 30 inch expansion rule.
https://frc-qa.firstinspires.org/qa/4
You’re right you can’t extend beyond 30in from your frame perimeter, this includes anything tethered to the robot (as far as I can tell).
In 2015, there was no extension limit, except that robots had to remain inside the field. 2019 is more permissive than the past few years, but nowhere near as permissive as 2015; all robot parts other than bumpers must start inside the frame perimeter, and be inside the frame perimeter when on the opposite side of the field. No robot parts are allowed to stray beyond 30" outside the frame perimeter, including the endgame. Attaching a part by a tether (unless it is quite short) is likely to result in a G24 violation this year.