Page 138 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

126 CHAPTER 6 Thrusters
Table 6.1 Thruster Comparison of Representative COTS Thruster Systems
Thruster Comparison
Prop Weight in Bollard Type Model Manufacturer Diameter Water Input Thrust
Electric Electric Electric Hydraulic Hydraulic
SPE-250 Sub-Atlantic 1002 Innerspace 8020 Tecnadyne SA300 Sub-Atlantic 1002MTL Innerspace
9.7 in. 246 mm 9.27 in. 235 mm 12 in. 305 mm 11.8 in. 300 mm 9.27 in. 235 mm
17.6 lb
8kg
41 lb
18.6 kg 34
40 lb 15.5
18 kg 22 lb
10 kg 20 lb 9.1 kg
600 VDC
600 VDC
600 VDC
26.8 hp 20 kW 21 hp 15.7 kW
220 lbf 100 kgf 665 lbf 302 kgf 505 lbf 230 kgf 700 lbf 318 kgf 639 lbf 290 kgf
same plane of motion, a counter-reaction to this turning moment will result. Just as the propeller of a helicopter must be countered by the tail rotor or a counter-rotating main rotor, the ROV must have counter-rotating thruster propellers in order to avoid the torque of the thrusters rolling the vehicle, especially in the smaller observation-class vehicles, counter to the direction of propeller rotation. If this roll does occur, the resulting asymmetrical thrust and drag loading could give rise to course deviations—the effect of which is known as “torque steering.”
Thruster location is critical to the performance of the vehicle as is the choice of the type of thruster. Design and performance data on similar sized thrusters from several leading manufacturers is presented in Table 6.1. The electric examples all use brushless DC motors. Most of the manufac- turers make a wide range of thrusters, although the Sub-Atlantic example is their largest electric thruster. Images of the thrusters are also provided (Figures 6.5
6.7).
6.1.3 Thruster design
Underwater electrical thrusters are composed of the following major components:
• Power source
• Electric motor
• Motor controller (this may be part of the internal thruster electronics or may be part of a driver
board in a separate pressure housing)
• Thruster housing and attachment to vehicle frame
• Gearing mechanism (if thruster is geared)
• Drive shafts, seals, and couplings
• Propeller
• Kort nozzle and stators