### Author Topic: robot motor factor  (Read 2840 times)

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#### kennykck

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• Posts: 43
##### robot motor factor
« on: December 17, 2007, 08:47:48 AM »
how do i derive this formula? or is there any website i can refer to?

Torque * rps > = Mass * Acceleration * Velocity / (2 * pi)

#### Steve Joblin

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##### Re: robot motor factor
« Reply #1 on: December 17, 2007, 09:26:41 AM »
I think this is what you are looking for... http://www.societyofrobots.com/RMF_calculator.shtml

#### kennykck

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• Posts: 43
##### Re: robot motor factor
« Reply #2 on: December 17, 2007, 09:34:08 AM »
i mean how do i start derive it until the end of that equation?  Coz i need write it into my report of robot design. Can anyone help?

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##### Re: robot motor factor
« Reply #3 on: December 18, 2007, 02:02:44 AM »
Torque * rps > = Mass * Acceleration * Velocity / (2 * pi)

(kg*m^2/s^2)* (round/s) = (kg)*(m/s^2)*(m/s)/(2*pi)

Do the units even match up? Given 1 round = 2 pi radians, and assuming the (2 * pi) is in radians, the radians are not on the same side (one is in the numerator, the other in the denominator).

To derive it you would probably start from F = m*a (force = mass * acceleration), T=F*d (torque = force *distance), and some rotational mechanics like Torque = I *alpha (torque = I * angular acceleration), where I= moment of inertia and alpha = a/r where r is radius.

#### kennykck

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• Posts: 43
##### Re: robot motor factor
« Reply #4 on: December 19, 2007, 08:27:02 AM »
From this site(http://www.societyofrobots.com/mechanics_dynamics.shtml)

v = 2 * r * PI * rpm      or      rpm = v / (2 * r * PI)

T = F * r

F = m * a

so, T/r = m * a      or      T = m * a * r

multiply rpm into the equation,

T * rpm = m * a * r * v / (2 * r * PI)
T * rpm = m * a * v / (2 * PI)

But why the website says

"Torque * rps > = Mass * Acceleration * Velocity / (2 * pi)

RMF = Torque * rps "

I'm confused...

#### kennykck

• Jr. Member
• Posts: 43
##### Re: robot motor factor
« Reply #5 on: December 19, 2007, 12:17:00 PM »
i mess up abit by the unit conversion

Velocity = 2 * radius * pi * rpm

Is my velocity in unit meter per second when using that formula?
I'm confuse whether it's second or minute...

#### JonHylands

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##### Re: robot motor factor
« Reply #6 on: December 19, 2007, 12:44:01 PM »
If you want meters per second, then do this:

Velocity = 2 * radius * pi * rpm / 60

or

Velocity = diameter * pi * rps

So, for example, a 600 RPM gear-motor turning a 2" diameter tire would be:

V = 2" * pi * 10 = 62.8 inches per second

If you wanted it in meters per second, the tire diameter would be 0.0508 m, so the velocity would be:

V = 0.0508 * pi * 10 = 1.6 m/s

- Jon

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##### Re: robot motor factor
« Reply #7 on: December 19, 2007, 01:54:25 PM »
rpm is equivalent to rps, just different units of time (minutes vs seconds)

#### airman00

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##### Re: robot motor factor
« Reply #8 on: December 19, 2007, 02:39:32 PM »
meaning
rpm / 60 = rps
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##### Re: robot motor factor
« Reply #9 on: December 19, 2007, 05:39:25 PM »
Quote
Coz i need write it into my report of robot design.
don't forget to reference my site

(I lost a lot of braincells and social life to figure out and derive that equation)

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