Will a 1/3 horse power sump pump motor burn up at half power?

[Ian Curtis]

Power is measured in Watts. Energy is measured in Joules.

Work and Energy have the same units. Power and Energy do not. Think about it, to find power Power you take the derivative of work with respect to time. This will divide the units of work by time.

[kevin.li.rit]

Originally Posted by EricH

150 kJ << without my telling you, is this power or energy?

Well thats energy because power would be j/s.

And I don't think its torque because you're not taking the cross product

[Ian Curtis]

Originally Posted by Coffeeism

Well thats energy because power would be j/s.

And I don't think its torque because you're not taking the cross product

Sure you are! Provided the force vector and radius vector are perpendicular, we can write the cross product as the following determinant:

i j k
0 r 0
0 0 F

Which simplifies to t=rF.

There might be some trig figuring out the force perpendicular to the radius, but it's definitely a torque.

[EricH]

Darn it, that's what I get for trying to do thermodynamics and dynamics-type unit-crunching after 11PM when I've got a headache. At least I'm not trying my homework in said subjects at this time...

As for torque, the only time it wouldn't share units with power would be if the force generating it was directed directly away from the axis of rotation, along the radius vector. Then torque goes to zero. Or if the force is acting at the axis of rotation, directed away from it (or towards it).

As long as you can get a component of force that is perpendicular to the radius, at a distance greater than zero, you can get the torque. Force *distance, where the distance is specifically defined as the radius between the force and the axis of rotation.

A statics course uses the same type of math to calculate the moment on a point in a beam.

[Al Skierkiewicz]

Al,
It not a simple matter of voltage in this case. A motor turns by using magnetic fields. In DC motors, the fields are generated via permanent magnets in the case and the current through the windings. In AC motors, there is generally no magnets and no brushes. The magnetic fields are generated by the AC current flowing through the motor windings and the induced currents that flow in other structures in the motor. Connecting this sump motor to a DC battery would cause it to heat up over time but it would never move.

[PAR_WIG1350]

Torque is measured using units such as oz-in and in-lbs, in refers to the radius of the shaft, wheel, or gear (etc.) in or lbs refers to the tangential force. The lack of a slash or the word per tells you there is no division involved. torque is the product obtained by multiplying the force tangent to the radius times the radius.
For example, all of these will yield the same torque ratings:

• 1 lb of force tangent to a 6 in radius wheel
• 2 lbs of force tangent to a 3 in radius wheel
• 8 oz of force tangent to a 1 foot radius wheel
• 1 oz of force tangent to an 8 foot radius wheel
• 6 lbs of force tangent to a 1 in radius wheel
• 48 lbs of force tangent to a .25 in diameter (.125 in radius) shaft
• etc

For all of these the torque is 6 in-lbs, or 96 oz-in. If you want more torque and you have large wheels, get smaller wheels. Wheelchair motors should be relatively strong. Most un-geared DC motors don't even provide more than 60 oz-in (3.75 in-lbs) of torque. CIMs provide alot at 343.27 oz-in (~21.45 in-lbs).

Also check out my response on this thread if you still want more powerful motors.
http://www.chiefdelphi.com/forums/sh...threadid=84877

torque converter

[Ether]

Originally Posted by EricH

As for torque, the only time it wouldn't share units with power would be if the force generating it was directed directly away from the axis of rotation, along the radius vector.

torque and power never have the same units. ever.

~

[Ether]

Originally Posted by EricH

150 kJ << without my telling you, is this power or energy?

It is energy (or work). NOT power.

Originally Posted by EricH

150 kN-m << That's power

No, it is not.


~

[EricH]

Originally Posted by PAR_WIG1350

Torque is measured using units such as oz-in and in-lbs, in refers to the radius of the shaft, wheel, or gear (etc.) in or lbs refers to the tangential force.

Correct, provided you're in one of the countries that still uses the English system of measurement for things like this. If you're not, N-m is the metric equivalent (and you'll need to convert it if you'd like it in English). [insert metric-English discussion here]

Ether, I'd like to invite you to read the whole thread before you respond. If you had, you'd have found that I'd already been corrected, and in a much more constructive manner than just denial.

[Ether]

My apologies if my replies to the questions you directed to me were too concise. I will be happy to explain, if you wish, and in whatever detail is necessary, the difference between energy and power, and between torque and power, and between force and power. These are important concepts for robotics and it would be a shame to misinform students who are just learning these concepts.


~

[EricH]

I'm a college student, so I know them. I just got confused. If you tell me that you've never gotten confused when it's late at night/early in the morning, I'll probably figure that you're lying.

[Ether]

I get confused sometimes, and I make mistakes too. But I don't lie. And when I am wrong and someone corrects me, I eat humble pie. I don't flame them.

~

[EricH]

Originally Posted by Ether

And when I am wrong and someone corrects me, I eat humble pie. I don't flame them.

~

It was not my intention to flame you.

However, when you compare two separate one-line statements that effectively say "you're wrong" and nothing else, to the responses that iCurtis and Coffeeism gave, which type of response is more constructive and still answers the question? (And, which one came earlier enough that I had time to read it, reply, and get some sleep?)

It gets kind of annoying when a question is answered thoroughly and then, as the discussion moves on, someone else answers it again without supplying any additional information, with enough time to read the answers already given.

[Racer26]

For those that are interested, 1075's powered forklift-cart is built atop the chassis of a power wheelchair, it used 24V motors, but we're running them at 12V on a 2004 IFI system, and all works fine. I suspect we may be shortening the life of the motors by running them on 12V, however, they're designed for long service-lives and our cart doesnt see a whole lot of use outside of on-season FRC competitions. We generally take our hand-cart to the offseasons held in smaller venues.

[Al Skierkiewicz]

Phil,
I don't think you are shortening the life of those motors. You are just running them at half speed.