Would it be ok to leave a computational device such as a phone connected to the robot via bluetooth on the starting tile to save space on the robot? If so, would it have to be physically mounted on the robot from the start and disconnected during the run or could it simply be placed on the starting tile next to the robot?
Robots can only use communication devices between robots.
If your robot communicates with an object placed on the start tile, it becomes a robot.
I think you are using two robots.
Therefore, such marks are not allowed.
However it is a interesting idea, please use other situation
What if the the phone was not placed on the starting tile by a human, but instead dropped off somewhere in the maze (possibly also on the starting tile?) by the robot. Would that be considered having multiple robots or would it count as the robot just dropping a part in the maze?
Section 3.4.2 of the rules (“Any parts that the robot loses intentionally or unintentionally will be left in the field […]”) implies that the robot can intentionally drop parts of itself in the maze. The word “parts” in 3.4.2 has been confirmed to include things other than rescue kits (such as objects for orientation) in this answer: Orienteering objects.
We will arrow a marker on the starting tile in 2019.
Of cause, markers do not have moving functions (like robots) and communication functions. After the start of scoring, the robot have to drop the marker itself. And you can not move the marker during the scor run.