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Thrust Calculation

Dear adam,
i am a newbie in ROV design, i have selected my bldc motor with torque 15.5 N.m , i selected the propeller with 2 blades 1045. i want to ask how much the motor generate thrust with these propellers, any formula or any calculation.
thrust calculation formula with propeller?
i am waiting for your response.

Hi @Muhammad,

There isn’t really a straightforward simple calculation you can do that will be very accurate, there are numerous factors that will affect things. In addition to needing a full torque/speed curve of the motor, small details of the propeller and nozzle design can make a large difference. This includes how much the propeller bends or vibrates under load, the surface finish, and other variables.

Some basic equations can get you roughly in the right range.

A better method is to use a motor simulation program together with fluid flow simulation software.

The best method and most accurate way to determine thrust is experimentally by just trying it, which is what we do for the most part.

-Adam

Really appreciated Adam,
can i ask you 1 more thing, when i go through some propeller thrust calculation, i found the propeller thrust formula which was using for drones in air, as they were using density of air in that formula, can i use that formula for water too by replacing it with air? is it a right approach?

Yes, that would be a good place to start.

-Adam

Hi @Muhammad,
propellers calculation is a complex but exciting task !, we did some a few years ago ( before Blue Robotics T100 & T200 ! ) with pretty good results.
We used a specialized software : Heliciel
Anyway, with small propellers, we had sometimes 30 to 50% difference between the calculated values and the measured ones.
Any change in dimensions, rigidity or surface finish had an influence on the result !

See below, a 3D printed prototype computed with Heliciel …

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Dear adam ,
I need your help again .
Adam , if i place the t200 thrusters in bluerov 2 at 60 deg instead of 45 , what will the change in thrust? Any formula or calculation ? To calculate the thrust and the direction of motion?
Waiting for your response.

Hi Muhammad,

Your thrust in the X or Y direction is just the trigonometric component of the vector.

For example, at 45°: ThrustX = sin(45°) = ~0.707, and ThrustY = cos(45°) = ~0.707

Similarly, at 60°: ThrustX = sin(60°) = ~0.866, and ThrustY = cos(60°) = 0.5

-Adam