Underwater Gearmotor GRM-1XXX

Blue Trail Engineering’s GRM-1XXX underwater gearmotors offer high reliability and performance at a fraction of the cost of similar subsea motors.  Their low speed, high torque, and optional position feedback make them suitable for applications such as crawler wheels, manipulators, drills, and brushes.

The GRM-1XXX gearmotors feature hard-anodized aluminum housings rated to 400 meters depth.  Their stainless steel output shafts are sealed with redundant seals that permit speeds up to 200 RPM.  The gearmotors can be mounted using the threaded holes on the output shaft end of the motor or by clamping to the outer diameter.

Similar to the Blue Trail Engineering underwater servos, these gearmotors are built using off-the-shelf motors installed in a custom enclosure.  This architecture makes it possible to offer a wide variety of gearmotor types at a low cost and with quick lead times.

Brushed Versions

 

For simple and economical operation, brushed versions of the GRM-1XXX gearmotor are available in various rated torques and speeds.  These come with a Cobalt 3-pin bulkhead connector, but only pins 1 and 2 are used (see Connector Pinouts below).  To control a brushed gearmotor, connect an off-the-shelf brushed motor controller or simply supply a voltage to the gearmotor.  The direction of rotation will depend on the polarity of the supplied voltage and the speed will depend on the magnitude of the supplied voltage.
 
Brushless Versions

Brushless versions of the GRM-1XXX offer greater efficiency and power.  They include hall sensors for position feedback and come with a Cobalt 8-pin bulkhead connector.  The user must connect a brushless motor controller (also called an “ESC”) to the gearmotor.  ESCs are available in “sensored” or “sensorless” versions.

A sensored ESC will drive the gearmotor using the hall sensors for position feedback, typically requiring all 8 pins on the connector (3 for the gearmotor windings and 5 for the hall sensor connections).  Some types of sensored ESCs will provide an output pulse that can be used to count the rotations of the motor, which is useful for applications such as wheels where the user wants the gearmotor to move an exact number of rotations.  Even if counting rotations is not required, a sensored ESC offers smoother control of the gearmotor at low speeds.  Use caution and follow the ESC manufacturer’s recommendations closely to ensure that the hall sensors are connected in the proper order.

A sensorless ESC, commonly used in hobby applications, can also be used to drive the brushless gearmotors.  In this case, only pins 1-3 on the connector are used.  Precise low-speed control is not as good with a sensorless ESC and position feedback is typically not available, although there are some models of sensorless ESCs that output a pulse for every motor revolution.

 

To connect your brushless gearmotor, use the Cobalt Connectors and Cables for Brushless Gearmotors for higher current capability.  These connectors and cables use 22 AWG wire instead of the 24 AWG wire found in the normal Cobalt 8-pin connectors and cables.