Underwater Robots - Gianluca Antonelli.pdf

5.3 Experiments of Dynamic Control 95
the presence ofacurrent asanirrotational, constant disturbance [127]. The
modeling aspects of including the current in the dynamic model hav ebeen
discussed in Section2.4.3. Since the measure of the current isnot available
in ODIN, ithas been taken into account asadisturbance τ v,C acting atthe
force/moment level on the vehicle-fixed frame. Moreover, since the number of
dynamic parameters could be very large (n θ,v > 100, see [127]) it was implemented
areduced version of the regressor matrix in order to adapt only with
respect to the restoring force/moments and tothe current. Inother words,
the control law implemented was the reduced controller of the one discussed
in Section 3.2.
The experiment was conceived in the following way: the vehicle had to
follow adesired trajectory with trapezoidal profile. Since the sonars need
to be under the surface of the water towork properly the first movement
planned was inthe z direction (see Figure 5.2 for the relevant frames). The
vehicle planned to move 2m in the y direction and 2m in the x direction.
23 m
x
O
diving pool
ODIN
y
y b
x b
arm
23 m
magnetic
north
Fig. 5.2. Sketch ofthe pool used for experiments with relevant frames
The control law has been designed using quaternions, however the specifications
ofthe desired trajectory and the output results are given in Euler
angles because of their immediate comprehension. Notice that the transformation
from Euler angles toquaternions is free from representation singularities.
The attitude must be kept constant atthe value of
η d,2 =[0 0 90] T deg .
Since the vehicle is not perfectly balanced, atrest, i.e., with the thrusters off,
its position is φ ≈ 5 ◦ and θ ≈ 15 ◦ with the yaw depending on the current.
The desired orientation, thus, is aset-point for the control task.