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

[Weird Al/ Tony]

alright thanks. ya see I'm trying to get a powerful motor that will be hard to stop while it is receiving power. that way it will be able to power my robot through all opposition. (this robot is for like a hobby, not the competitions) and I'm thinking that I have some older wheelchair motors, and other stuff. but they arent very fast and they dont have much power. I'd probably need either a gear box or some good belts to allow diffrent speed and torgue. I kinda think I know what i'm talking about. I mean I'm just getting on a team so I dont have alot of robotics experience.

[kevin.li.rit]

Originally Posted by Weid Al/ Toni

alright thanks. ya see I'm trying to get a powerful motor that will be hard to stop while it is receiving power. that way it will be able to power my robot through all opposition. (this robot is for like a hobby, not the competitions) and I'm thinking that I have some older wheelchair motors, and other stuff. but they arent very fast and they dont have much power. I'd probably need either a gear box or some good belts to allow diffrent speed and torgue. I kinda think I know what i'm talking about. I mean I'm just getting on a team so I dont have alot of robotics experience.

Go FIRST Retro and use some 12 Volt Drill Motors. They'll come with gearboxes with high low speeds too! Judging by your team number your team might still have some.

[EricH]

I think that you may want to talk to your local physics teacher. At the least, he can help you through some of the concepts and the math behind them.

I'll give a brief rundown of some of them.

Voltage: difference in electrical potential energy between two points.
Amperage or current: how fast that electrical energy can move.

Power (or energy): force*distance.
Work: power/time.
Torque: force * distance, usually referenced with regard to rotational motion. You'll want to know this eventually.

Gearboxes multiply and divide torque and rotational speed, which translates via wheels to linear power and linear speed.

BTW, you may want to look up some of John V-Neun's whitepapers. I think that those will help you with some of the math that is behind the design of a drivetrain, and quite possibly help you optimize the drive for the motors you have.

[Ether]

Originally Posted by EricH

Power (or energy): force*distance.

power and energy are not the same thing.

Originally Posted by EricH

Work: power/time.

you have that backwards.

power = work/time

Originally Posted by EricH

Gearboxes multiply and divide torque and rotational speed, which translates via wheels to linear power and linear speed.

torque translates to linear force, not linear power.


~

[EricH]

Originally Posted by Ether

power and energy are not the same thing.

They aren't, but for some reason known to nobody, they share the same units. Joules in the SI, BTU and its equivalents in the Eng. system. (Eng. == either English or Engineering, which for functional purposes are indistinguishable.) This makes the calculations very similar when all's said and done.

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

150 kN-m << That's power, but to get that I had to expand the unit. Also note that that is a torque unit as well.

Energy has a number of ways to get to the kJ unit, none of them simple. Something about energy/mass * mass in a number of weird combinations makes it a little hard to translate out of handwriting.

[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.

[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.

~

[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

[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.