M100 Motor Documentation


The M100 Motor is a brushless electric motor for use underwater. It is pressure resistant and ruggedized against harsh ocean conditions. Many of the motor’s components are used in the T100 Thruster.


Always practice caution when you’re working with electricity in water and with the spinning blades of the propeller. Keep body parts away from the motor to avoid injury.


The M100 Motor is easy to install in many different applications. It was designed with mounting holes that are identical to those found on many common brushless motors.

Video Tutorial

Electrical Connections

Connecting to an External ESC

The motor has a solder pads to connect to three wires. These three pads must be connected to the three motor wires on the electronic speed controller (ESC). The order does not matter, but if the motor direction is the reverse of what is desired, switch two of the wires.

The three solder pads are always connected to the same motor phases, so connecting in a consistent fashion will result in all motors rotating in the same direction.

Sealing Connections

We recommend using the following compounds to seal the soldered wire connections on the M100 Motor.

  • Loctite Marine Epoxy works well at great depths and is very thick so that it can be applied in one coat.
  • MG Chemicals 4229 is a rubberized coating that can be used at shallow depths (less than 100ft) and is removable if required.


The motor requires a brushless electronic speed controller (ESC). If you are using the BlueRobotics BasicESC or BlueESC, please see the appropriate product page for instructions.

Clicking Noise

If you hear a clicking noise during operation, especially when operating in air, do not be alarmed. It’s normal.

The motor uses solid plastic bushings and due to the tolerances of the bushings and motors shafts, the shaft can move slightly in the bearing. The noise is drastically reduced or eliminated when operated in water. The water acts as a lubricant for the bearings and smooths operation.

Care and Maintenance

Normal Care

During normal use:

  • Rinse with fresh water after use in saltwater to minimize the accumulation of salt deposits.

  • Rinse after operating in sandy environments to remove sand particles.

If operated for extended periods in the water:

  • Occasionally clean biological fouling and mineral deposits from the motor or performance may be impacted.


Occasionally it may be necessary to disassemble the motor. Here is a quick guide on how to do so!


The motor does not start

This is usually an issue with the proper commands being sent to the ESC. Please see the ESC documentation for instructions on how to operate the ESC properly.

The motor does not start but the propeller tries to move.

This can be caused by a disconnected motor wire or a short between motor wires. Check that all three motor wires are connected and not shorting. To do this, check resistance of each phase pair in the thruster. Each thruster wire phases pair (Blue/green. blue/white, green/white) should have the same resistance within 0.1-0.2ohms or so. If no connection is read or one pair has significantly higher resistance, your thruster has a fault. Please e-mail support@bluerobotics.com if this fault is found.

The motor is jammed when turned by hand.

This can be caused by something jamming the propeller or by major internal damaged caused by overheating, short circuits, or heavily worn bearings. Please disassemble the motor and inspect for damage or blockage.


For all the engineers out there, here’s some more info.

Test Results

Check out the test results section for the T100 Thruster, which shares most of the same components as the M100.

Quality Control

We perform the following tests on every motor before they are shipped.

  • Insulation Test, also know as a hipot test. We submerge the motor in water and measure current leakage at high voltage (250V) to ensure that the insulation is sufficient.

  • Spin Test. The motor is operated in air across the entire speed range to ensure that it operates correctly.

  • Visual Inspection. Each motor is inspected for visual issues or damage.