TABLE 10.9 COMPARISON OF ELECTRIC AND HYDRAULIC MOTION ACTUATION SYSTEMS 



[FROM REF. (32)1 



Electric 



Hydraulic 



• Electromechanical systems are expensive 



• DC motors start and stop smoothly 



• High-torque low speed DC motors are heavy and bulky 



• Small AC and DC motors require high speed operation, which 

 requires clutches, gear reduction, and brakes to provide 

 adequate motion characteristics 



• Foreign to the seawater environment so must be oil-filled. 

 Seawater intrusion usually results in system failure. 



• Brush Insulation must be prevented by increasing contact 

 force, thereby reducing operating life and reliability 



• Internal wiring easily accomplished eliminating snagging 

 problems 



• High and low speed continuous rotation easily obtained 



• Hydraulic systems are less expensive than electromechanical 

 systems 



• Compatible with the environment 



• High power to unit weight ratio allows use of small components 



• I nternal leakage of fluid allows drift, overshoot and loss of ef- 

 ficiency 



• External leakage degrades efficiency but may not abort the 

 operation 



• Motions automatically braked by closing of control valve 



• Simple overload protection provided by relief valves 



• External hosing causes snagging problems, internal fluid routing 

 is complex 



• Pressure compensation, required for a lightweight system, pre- 

 vents arm use while changing depth 



• Continuous rotation actuators unreliable 



Fig. 10.39 Manipulators of a| SEA OTTER, b) SHELF DIVER, cl DS-4000, d) STAR II, el NEREID 330 and fl PISCES III 

 (b. Perry Sub. BIdrs., c. NAVOCEANO, d. Gen. Dyn. Corp.. e. Nereid nv, f. HYCO) 



526 



