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# Physics/Fan motor to torque conversion

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QUESTION: Sir i want to that how i calculate a motor having a fan power to torque in NM.. I m creating a homemade toy in the form of maglev train
sir pls provide me a simple short formula for this-
i have a torque of 2kg in a form of maglev train Acceleration is 30sec final distance 1ft (means i want distance travel 1ft in 30sec)
but i don't know that which type of motor i want to use how much power,rpm, fan size, fan dia,no. Of fan blades,motor rpm, fan rpm etc etc.
sir pls provide me full formula about this using above example pls reply me as soon as passable

ANSWER: Wow, there is no simple formula for that.  2kg is not a torque, it's a mass.  You have no idea what size of fan, or shape, or how fast it will spin?  I mean, I'll make some assumptions here that you're using a relatively small fan (2 kg and it's described as a toy moving on an almost frictionless surface) to move something only 1 ft in 30 seconds.  That means it needs an acceleration of only 1/15 m/s^2, which is less than 1% of Earth's gravity...so a tiny fan motor (I have one for self-cooling that has a 2cm wide motor) would do, they produce way more torque than you'd need at about only 2 Nm.

I'd really need a lot more detail about the fan and the rotation rate to figure out anything related to torque from the motor.  These are pure guesstimate figures.

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QUESTION: 12v 1.3A dc motor 3000rpm fan size 1Inch motor efficiency 70%
this is a toy motor and mass is 2kg including motor and system
on frictionless surface means as in a form of maglev train
now i want to know what is exact rpm and torque of motor to move 2kg mass final distance 1ft in 30sec acceleration 30sec
and if motor power is more than this....then what is maximum torque of motor for 1ft in 30sec distance as 2kg or < 2kg
And what happen if i use very low motor as 3.5rpm or 10motor same fan size then what is torque?
in fan motor and normally pulley motor Torque formula is same or different
sir pls give a formula for fan motor torque as using above example @ variable rpms and fan size i mean what what happen if i use fan size 2Inch instead of 1inch is torque decrease or increase or anything else
provide me some examples of fan size motor torque....reply soon sir

Answer
3000 rpm is 50 rotations per second...that's a very high-powered motor for this application.  You're only talking about 1/150th of a g of acceleration.  The torque on the fan motor would be constant for driving a fan, of course, at such low speeds.  I still have no idea what the pitch of the fan is, how many blades it has, etc.  This really is more of a question for an engineer.  Direct testing is really the way to solve this, theory will contain many inherent errors in the transmission of force via the fan.

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#### Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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