Change in Motor

After further consideration of designing the planetary gearing system, it has been concluded that it may be susceptible to clogging from debris in the water environment.

To avoid this a new brushless motor with a slower RPM and higher torque has been selected.

It has a given Kv of 380. This can be used to calculate the theoretical torque of the motor using the formula T=Kt*I (eric, 2015), where T is torque, Kt is the torque constant and I is the applied current. Kt can be calculated by Kt=1/Kv. (eric, 2015)

If our current supply in around 9A then our theoretical torque will be, T=(1/380)*9=0.02368Nm.

motor2Screen Shot 2017-02-12 at 20.04.42.png

Since our propellers are 50mm in diameter this torque should sufficient enough to allow the propellers to turn through the resistance of the water.

The Kv is also a good indicator of the RPM/volt applied tot he motor (in air). So out of the water we expect the motor to turn at 4560 RPM, as we are using a 12v supply.

These torque calculations seem to be too low however so a simple test will have to be done to confirm the torque.


eric, 29 july 2015. meaning of motor kv. [online]. Learning RC [accessed: 01/02/2017]. available from:


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