Why is it difficult to find a small electric motor with 2000RPM and good torque?

[stimulisRK]

I've been looking on Mcmaster Carr and Digi-Key for a small electric motor. It needs to be a 2000RPM motor but also to produce a torque preferably greater than 1 N-m, but less than 1.6 N-m. The torque really can be anything though, i'd just like it to be greater than 1 N-m

I'm having trouble finding motors with these conditions. It seems like anything running at 2000RPM has an extremely small torque. There are a lot of motors producing good torques I like, but they're only 1800 RPM max. Any ideas?

Thanks

 

[pantaz]

I would check online surplus stores, such as http://www.youngssurplus.com/" , etc.

 

[BadBrain]

stimulisRK:

I think you're asking the impossible.

Torque is inversely proportional to rotational velocity (RPM's).

See:

http://en.wikipedia.org/wiki/Gear

and note the caption to the animated diagramme to the right of the first five paragraphs, which caption reads:

"Two meshing gears transmitting rotational motion. Note that the smaller gear is rotating faster. Although the larger gear is rotating less quickly, its torque is proportionally greater." [Emphasis is mine.]

***

Torque is brute force applied to heavy resistance, whereas high RPM's imply minimal resistance. One of my favorite illustrations of this point is the helicopter; in order to generate lift, the rotating wings must move through the air at high velocity (i.e., high RPM's are required), This means little torque is available to cut through the aerodynamic drag applied by the air against the rotating wings of the helicopter, which, in turn, means that the air may well resist the rotor blades to the extent of forcing the fuselage to absorb the rotational motion applied by the engine to the rotor blades by spinning around beneath the rotors, which tendency requires a tail stabilizer rotor:

or twin contra-rotating rotors:

[PLAIN]http://cdn-www.airliners.net/aviation-photos/middle/5/9/9/1735995.jpg

to overcome.

Another of my favorite examples of this phenomenon is my model steam engine; I usually engage it to a toy workshop just to give it something to work against (i.e., to absorb power by converting excess RPM's into torque). When I disengage my engine from the workshop, the RPM's go through the roof. (I try not to do that for fear of harming my engine.)

 

[pantaz]

stimulisRK:

I think you're asking the impossible.

Not really, assuming that a "https://www.google.com/search?q="gear+motor"&"" is suitable for the project. Gear motors come in all sizes, speeds, and power specs.

 

[BadBrain]

Not really, assuming that a "https://www.google.com/search?q="gear+motor"&"" is suitable for the project. Gear motors come in all sizes, speeds, and power specs.

OK, so now you've really confused me. The purpose of reduction gearing is to convert RPM's into torque. You really can't have both at the same time.

Can you here provide an example of a motor which meets all of StimulusRK's criteria?

 

[Juval]

Torque is brute force applied to heavy resistance, whereas high RPM's imply minimal resistance. One of my favorite illustrations of this point is the helicopter; in order to generate lift, the rotating wings must move through the air at high velocity (i.e., high RPM's are required), This means little torque is available to cut through the aerodynamic drag applied by the air against the rotating wings of the helicopter, which, in turn, means that the air may well resist the rotor blades to the extent of forcing the fuselage to absorb the rotational motion applied by the engine to the rotor blades by spinning around beneath the rotors, which tendency requires a tail stabilizer rotor:

or twin contra-rotating rotors:

[PLAIN]http://cdn-www.airliners.net/aviation-photos/middle/5/9/9/1735995.jpg

That is quite incorrect. The contra-rotating force imposed by the rotor head that causes the helicopter's fuselage to yaw is due to the fuselage's mechanical advantage over the rotor head. Or have you ever seen a helicopter whose rotors weight more than the fuselage?

Also, those helicopters are all using in-superior internal combustion technology. They are severely underpowered rendering an atrocious power/weight ratio. They are not made for performance.

I dare you to say "little torque is available" again.

https://www.youtube.com/watch?v=eVpZFsPdgkg

 

[Juval]

I've been looking on Mcmaster Carr and Digi-Key for a small electric motor. It needs to be a 2000RPM motor but also to produce a torque preferably greater than 1 N-m, but less than 1.6 N-m. The torque really can be anything though, i'd just like it to be greater than 1 N-m

I'm having trouble finding motors with these conditions. It seems like anything running at 2000RPM has an extremely small torque. There are a lot of motors producing good torques I like, but they're only 1800 RPM max. Any ideas?

Thanks

I bet you haven't considered outruners.
And how are planning to power this motor? That might be helpful to know don't you think?

 

[pantaz]

OK, so now you've really confused me. The purpose of reduction gearing is to convert RPM's into torque. You really can't have both at the same time.

I assumed 2000 rpm referred to output speed, not input.

Can you here provide an example of a motor which meets all of StimulusRK's criteria?

Well, it's not an exact match, but two minutes of searching found this (not a gear motor):
http://www.batteryspace.com/DC-Motor-Heavy-Duty-24V-DC-Motor-750W-2600RPM-28A-rate.aspx
The http://www.batteryspace.com/prod-specs/5376.pdf" says 1.6 NM, 2600 max rpm.

Also, "small electric motor" leaves a lot open to interpretation.

 

[BadBrain]

I assumed 2000 rpm referred to output speed, not input.

Well, it's not an exact match, but two minutes of searching found this (not a gear motor):
http://www.batteryspace.com/DC-Motor-Heavy-Duty-24V-DC-Motor-750W-2600RPM-28A-rate.aspx
The http://www.batteryspace.com/prod-specs/5376.pdf" says 1.6 NM, 2600 max rpm.

Also, "small electric motor" leaves a lot open to interpretation.

Thanks!

Somebody sure did a heck of an engineering job on that little motor.

 

[BadBrain]

That is quite incorrect. The contra-rotating force imposed by the rotor head that causes the helicopter's fuselage to yaw is due to the fuselage's mechanical advantage over the rotor head. Or have you ever seen a helicopter whose rotors weight more than the fuselage?

Also, those helicopters are all using in-superior internal combustion technology. They are severely underpowered rendering an atrocious power/weight ratio. They are not made for performance.

I dare you to say "little torque is available" again.

https://www.youtube.com/watch?v=eVpZFsPdgkg

Actually, in the case of your video, a great deal of torque is observable, in the form of mechanical resistance of the air against the rotor blades, causing uncontrolled contra-rotational fuselage yaw on the part of the little helicopter, which crashes regularly throughout the video.

The greater mass of the fuselage relative to the rotor blades (in a real helicopter, as opposed to the little model) should allow inertia to control contra-rotational fuselage yaw. The fact that it doesn't, and that a tail-rotor or contra-rotating twin rotors are required to counteract the mechanical pressure of the air against the rotor blades in order to prevent uncontrolled contra-rotational fuselage yaw, is clearly an example of torque gone wild.

Perhaps I should have said that little torque SHOULD be available, if the rotor blades are to gain the RPM's (i.e., absolute airspeed) needed to allow them to generate lift. The general case is that high RPM's and high torque are incompatible; a helicopter, in effect, offers a choice between the two, against which counteracting forces need to be generated to insure the victory of lift-generating RPM's over fuselage-spinning torque.

And it's not that helicopters are underpowered; they can't possibly exhibit high performance, due to the natural instability induced by the rotating wings. It seems to me that a high-powered engine on a helicopter would produce the effect apparent in your video (which I strongly suspect is over-engined): a helicopter flopping around on the ground like a fish out of water. Funny to watch when it's just a model helicopter, but unsurvivable for a pilot on a real helicopter.

And, what is the source of your disappointment over helicopters having internal combustion engines? While I'm totally in love with steam, I can guess that a steam-powered helicopter might be a bit impractical. If you can build a working version to prove me wrong, I'll gladly stoke the boilers!

***

EDIT:

I stand by my original post. "...in order to generate lift, the rotating wings must move through the air at high velocity (i.e., high RPM's are required), This means little torque is available to cut through the aerodynamic drag applied by the air against the rotating wings of the helicopter, which, in turn, means that the air may well resist the rotor blades to the extent of forcing the fuselage to absorb the rotational motion applied by the engine to the rotor blades by spinning around beneath the rotors...". What I meant is that the high RPM's of the rotor blades fail to generate enough brute torque to prevent the air from resisting the blades' passage through it to the extent of preventing uncontrolled contra-rotational fuselage yaw. Your video actually proves my point.