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Flow rate/s for T200?


(Joshua) #1

Hi there, I am using a T200 for a project and don’t have access to a flow meter and would like to know if there is a way to simply calculate the flow rate of the T200 Thruster at a certain thrust.

For example at 12V and 4.6A (according to the graphs on the store page) the thruster generates about 55W of power and a thrust of 2.91Kg f. Is there a way to convert these values to flow rate?

Also is it possible to add a graph of the flow rates to the store page if these values have already been measured?

Thanks in advance.


(Adam) #2

Hi @Josh_Huysamen,

We don’t currently have the tools and not yet measured the flow rate or flow speed of our thrusters. However, you are right that with some estimates and math we can get to a reasonable rough theoretical value for these, at least under ideal conditions.

The T200 propeller has a 76.2 mm outer diameter, and a 40 mm diameter central hub. It also has a pitch of 22.5° at 75% of its radius, and spins at about 3075 RPM full throttle 12 V, and 3600 RPM 16 V. Using the pitch and and RPM approximation, this results in a theoretical maximum flow speed of 4.45 m/s at 16 V, and 3.80 m/s at 12 V. The propeller has an area of about 0.00330373 m^2. Multiplying these area by the flow speed results in a volume of about 0.014702 m^3/s (or 14.7 liters/s or 3.88 gallons/s) at 16 V, and 0.012554 m^3/s (or 12.5 liters/s or 3.32 gallons/s) at 12 V.

Note that the 55 W power number you mention is not the power generated by the thruster, rather the electrical consumption. The actual mechanical power will be lower due to the efficiency of the thruster.

Bear in mind these speeds and flow rates are rough estimates based on some math and not true measurements, I would expect the real number to be lower. However, they should be reasonably accurate for estimation purposes. I hope this helps!

-Adam


(Joshua) #3

Hi @adam

Thank you for such an informative response, it is much appreciated. I only needed rough estimates and this will definitely help.

I would just like to ask if the flow rate would be a linear change with a change in RPM?

Thanks again


(Adam) #4

Glad to help! Yes, flow rate will be linear with a change in RPM.


(Joshua) #5

Hi again @adam

Might be a simple question but is the RPM also linear to the PWM signal? So for instance will the RPM change linearly between the reverse PWM range of 1100us - 1500us?

(I am trying to figure out what RPM the motor is running at a certain PWM, so i can then roughly calculate the flow rate from what you said previously).

Thank you in advance!
Joshua


(Patrick José Pereira) #6

Hi Joshua,

Take a look in this post, this may be useful for you:

Doing some fitting with a linear equation, you can find that RPM/PWM can be approximately linear, but it depends if the margin of error is ok for you.
image

A 3rd order one could be more precise for you:
image