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Motion System Design
Under-the-ocean motion

Under-the-ocean motion

Whether exploring sacred underwater caves in the Yucatan or pursuing elusive Arctic sharks, tiny ROVs, or remotely operated vehicles, are reaching new depths. But VideoRay LLC, Exton, Pa., holds the distinction of making the world’s smallest ROV.

The submersibles, which weigh only 8 lb, can maneuver into tight or enclosed spaces hazardous for divers. They essentially provide a set of eyes underwater: A video eye visually captures the underwater world, which can be recorded or viewed live by a topside crew.

Pittman brush-commutated dc motors from PennEngineering Motion Technologies in Harleysville, Pa., power all VideoRay ROVs. “From the start, our specifications were exacting,” says Marcus Kolb, director of Research & Development at VideoRay. The most challenging specs involved the motor’s finely polished shaft, where the ROV’s propeller head attaches. The shafts must be extremely smooth and hard, according to Kolb, and VideoRay insists on machining its own shafts using a proprietary process. The shafts are then supplied to PennEngineering Motion Technologies to integrate motor (and seals) into the shaft housing.

Every ROV includes three Pittman Lo-Cog brush motors. Two are in tubes on either side of the ROV for horizontal thrust, and another is in the center of the main hull for vertical thrust. All enable reversible movement and perform without gears.

Kolb says the Lo-Cog Series 9000 motors proved a perfect fit for the design envelope: They are 2.2-in. long, weigh 8.9 oz, and can achieve a peak torque of 31.6 oz-in. The motors feature seven-slot skewed armatures to minimize magnetic cogging (or reluctance torque) even at low speeds (as in this ROV application), which promotes smooth operation.

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