Question L1-C3

The question is about the degrees of freedom and degrees of motion of a mobile robot. The question is: For an artist, we have to design a robot able to deposit sand on the ground to make a drawing. The basic test will be to draw a square. The robot will have to draw the full square, made of four segments joined at 90 degrees angles, at constant speed. This because the sand is falling also at constant speed and the full square needs to be perfectly homogeneous (same thickness, same width on the whole square). Which design choice do you make?

Answer A: DOM do not play a role here as we draw a line. You can take a differential drive
robot, cheap and efficient, depositing sand in the middle of the robot.
This answer is not correct: As the sand falls at a constant speed you will have bigger pile of sand in the corners if the robot is differential and has to turn on the spot.
In the explanation of the student we would like that the student mentions that the degrees of motion are limited here, requiring to turn on the spot to access another dimension. 

Answer B: Here we need to be omnidirectional, even if non-holonomic like the synchro-drive,
able to orient the wheel in any directions and then move, without turining the body.	
This answer is not correct: Also here the synchro-drive that has to stop and turn, before continuing, which will create piles of sand. 
In the explanation of the student we would like that the student mentions that also in this case the degrees of motion are limited, requiring to turn on the spot to access another dimension. 

Answer C: DOM play a role here. You need to take an holonomic robot. This structure allows to
take any direction without stopping.
This answer is correct: To have a continuous movement despite the 90 degrees turn you need to access at least the two cartesian coordinates directly, meaning that you need at least those two degrees of motion (DOM). 
In the explanation we would like that the student mentions that for this task the DOM have an important role, requiring continuous motion in at least two degrees of freedom.
