Fastest Rotation Of An Electric Motor

In the case of a series-wound motor under no-load conditions, the speed which will achieve its destruction.

Well... i saw an article a couple of years ago about Dyson vacuums. They claim they have a brushless DC motor which can obtain speeds upward to 100,000RPM!!!!! That seemed on the upper limits of feasible (not sure on what bearings you'd need in that application). I know that 25,000RPM on a brushed DC is completely obtainable.

Indeed. Many motors intended for use in model construction can go north of 35,000rpm at 12VDC, particularly the smaller ones. In the limit, the shaft speed depends upon the quality of the bearings and any gearbox, as correctly indicated.

I once maintained a bunch of ID grinding macines that used a high speed motor/spindle that turned at 38,000rpm run by special generators, can't remember the electrical specs. They used Barden angular contact bearings with a air mist lube system. Electrical and mechanical failures were always good for lots of sparks!!

Please go to Turbocor a Danfos company. They have an oil free a/c compressor that turns 38-44,000 rpm with no contact between the rotating shaft and the rest of the motor. It works and it is amazing.Start up amps for a 100 hp compressor is less than 2 amps to start rotation.

"Start up amps for a 100 hp compressor is less than 2 amps to start rotation."

Wow! That seems like a low starting amperage.

The NC drill I have here at work, the windings are epoxy filled and very well balanced.

The specs on this motor are 10k-60k RPM

Some of the drills I have here (0.25mm) for drilling FR4 (fiberglass) are rated for about 125-130k RPM

Highest RPM i have experienced is AC spindle in CNC 3axis router reaching almost 70,000rpm max , but have observed certain technologies that reach 3,00,000RPM , like flywheel mechanical battery that utilise DC brushless ,magnetic bearings and vaccum condition with low eddy currents , some air driven motors can reach 10,000,000 RPM ....only heard i too don`t believe it....

here is an example of an 500'000rpm application

ftp://ftp.elet.polimi.it/users/Alberto.Carrera/APEC2006/data/8.1_10229.pdf

Check this link: http://www.lbl.gov/tt/techs/lbnl1939.html for a VERY fast motor, claimed to be capable of 1,000,000,000 rpm. It is covered under US patent 7,053,520.

Hi,

what do you want to spin with a motor so small that you cannot see it with the best microscope?

Go to real things:

spindles for grinding and drilling with rotors near 20mm diameter and automatic chucks are used at speeds up to 180,000rev/min or 3,000rev/sec since 15 years, rotating in ballbearings or airbearings and drivenm by asynchronous motors.

These motors are a special type as the short circuit winding of the ASM are deposited as electrolytic copper in slots on the shaft of the spindle.

RHABE

what do you want to spin with a motor so small that you cannot see it with the best microscope?

It's a completely valid question. With MEMs (Micro Electro-Mechanical Systems) beginning to reach the market, I suspect that there are lots of valid answers. If you attached a spiral, you'd have a synthetic flagellum; build a large batch on a chip, and you'd have a pump useful for some of the chemical-lab-on-a-chip devices coming to fruition. The ability to work in a vacuum and at high temperature might make it useful on satellites in place of conventional motors, if the forces needed are low enough, or you can gear down (silicon gears and moving parts have already been built and demonstrated; "comb drives" are another route to miniature linear and high rotation rate motors). Use the rotor as a rasterizing mirror. These are off the top of my head prior to having my coffee - I'll bet that CR4 members can find lots more!

Hi Ron,

for all these application you did mention the motor has to be a factor of 10 to 100 bigger (linear) so the torque will be a factor of more than 1000 higher.

Vacuum or high temperature is not really an obstacle, most satellite components work in these environments, I myself did design some for cryogenic use and 10⁹ load cycles for flexure structures used in infrared scanning.

Tell me how a chemilab will work better with a 0.3µm pump instead of direct electrical drive?

For the near future there is a bright and increasing future for sensors but I do not see any motors to come. May be you find some real (likely to be realised) examples.

Any drives as the comb drives you mentioned are used either for making better acceleration or rate (coriolis) sensors or for the multiple mirror arrays.

So I am looking with interest to any use of below 1 µm sized motor.!

RHABE

RHABE- We may soon need to label this sub-discussion as OT, since the original question was simply "What is the fastest speed (RPM) that can be attained by a DC motor and an AC motor?". No "practical" considerations were implied.

I am somewhat missing why you believe that the motors would necessarily need to be so much larger to function. Observe how small archaeal flagella and their "motors" are, and note that they are extremely practical. Yes, the device I linked to would still need to be scaled up to reach that size, but the current work [as I understand it] has more to do with near-pure research, where proof-of-concept comes well before practical application, than to size or torque delivery considerations. And that is perhaps the direct answer to your earlier question: the "why" has to do with acquiring knowledge and capabilities. Application, if it occurs, come later.

For use as a mirror to sweep a beam of light, and given that the rotor is normally gold-coated already, wouldn't torque be inconsequential? Yes, the rotor has to reach sufficient size to reflect photons, and they will transfer momentum, but it should be possible to arrange things so that losses at one point of rotation are balanced by gains at another (impacts "with" and "against" rotation). Or direct the beam parallel to the motor axis, so that impact forces are taken by the bearing, and use as a chopper: where is the need for torque?

Hi Ron,

a motor is for my thinking only a device that can output some torque, speed and power.

If you think only about speed then I suppose that the electron circulating a hydrogen atom may be the fastest.

You are right about flagellae, this is a superb solution. I do not know how it is driven nor the materials of the bearing: is it like cell walls or like the silica sceletons of diatoms?

But nature has not managed neither a scale down nor a scale up version of this motor!

Considering the necessary torque for a big motor: there is the load torque, the inertia of the rotor and gears, the friction and at very high speed or very small gaps a significant amount of gas or fluid drag.

Considering a very small motor from these forces only the output torque to the consuming mecanism and the viscous drag is remaining.

This is because there is no possibility to raise the speed as fast as inertia is going down with diameter.

As the total force or torque any such device can produce is going down too the big problem of the small and MEMS world is friction, viscosity and capillary forces. In some applications may be additional losses to eddy currents.

These require quite a substantial amount of torque. Also in vacuum.

RHABE

An electron around a proton may be the fastest, but I think of a motor as being a device which converts energy from one form to another, with the output being mechanical rotation or linear motion. Input could be electrical, thermal, pressurized liquid or gas, chemical, etc. (In comparison, an engine converts fuel + oxidizer into energy and then outputs mechanical rotation / traverse / oscillation, or whatever.) Both of these are very loose definitions and subject to revision, interpretation, and refinement. Maybe more! Please feel free to adjust as you wish; just make sure that we are all working from the same assumptions and concepts if possible, or are at least aware of the other persons' assumptions and terminology.

A hydrogen atom, then, lacks the intake of energy, to fit the description that I've used. So do rotating pulsars or revolving solar systems or galaxies.

See http://en.wikipedia.org/wiki/Flagellum as one description of flagella and how they work. PBS (the Public Broadcasting System, television in the USA) showed some wonderful animations and SEM (Scanning Electron Microscope) photos of flagella as part of a description of the trial when the Dover, Pennsylvania, school board lost its bid to replace science with so-called Intelligent Design in the schools' textbooks and classrooms. (see http://en.wikipedia.org/wiki/Kitzmiller_v._Dover_Area_School_District for some background on the trial.) The ID proponents argued that the flagellum and its driving motor (chemical energy input) had to have come into existence as a complete system, but it was shown in court that perfectly useful stings for injecting venom use most of the same parts, and could easily serve as the predecessor functional entity in living organisms.

Oddly enough, it appears that friction and viscosity laws do not continue to scale "all the way down". I have read that bacterial flagella can reach thousands of rpm in liquid. Cavitation effects would prevent significant scale-up, I would guess, which may be why Nature hasn't done so. Using carbon nanotubes as bearings seems to solve a great number of problems that I would otherwise expect to exist at such scales.

In very high speed applications, air bearings or magnetic bearings are used to support the shaft.They use an air-foil principle or magnetic repulsion.

The maximum speed of a synchronous motor is determined by the number of poles and the freqeuncy of the applied a/c voltage.(FreqX120/ # of poles), so at 60 hz, the maximum rpm is 3600.DC motors are another matter altogether.I have seen series-wound dc motors disintegrate under no load conditions because the field current limits the rpm.(less filed current=more RPM) When the armature and field are in series, the amount of torque and speed is limited only by the capacity of the power supply, and the field current is very high at start up.(Very high torque, low rpm).As the rpm builds, the armature current decreases,the field current decreases,which increases rpm, which reduces field current, etc.Without sufficient load,it will continue to increase in speed until something gives. Usually the commutator explodes or the windings expand into the housing.

There is a flywheel battery which spins at a very high rpm that uses magnetic bearings for support, although I do not know the maximum rpm, it is extremely high, and uses a wound rotor made of very strong carbon fibers to endure the high G forces.

HTRN

"air-foil principle" or is it "Skin-effect"?

"air-foil principle" or is it "Skin-effect"?

I believe Guest (Post #10) did mean foil: see http://en.wikipedia.org/wiki/Foil_bearing for the reason. Note that guest mentioned BOTH air- and magnetic bearings earlier.

The Dental Surgeons HAND-Piece by Siemens [Brush-less DC Motor] had 72,000 RPMs in 1970s
[ probably named "Sirona" if I remember correctly ] & Air-Turbine Hand-pieces were well above its speed.
It was the 1st Brush-less DC Motor I came to know.

Beckman made an analytical ultrcentifuge model E (I think first made in 1947, but I recall seeing one at University of South Dakota in 1965). The motor and specimen rotor ran in a vacuum. To maintain spinning load balance, the specimen rotor hung from a flexible wire shaft which achieved some kind of self-compensating mass balance probably by means of centrifugal forces. It took hours to get up to speed, and hours to stop. The motor was dynamically braked electrically with the energy dissipated into a resistive load consisting of light bulbs (as I recall).

I don't recall the rpm, but the rotor was several inches in size, so the G-force was enormous; enough to stratify sugar solutions into density gradiants in which speciment components settled.

The rotor contained a hole, which passed through a schlerien optical system with each rotation, allowing the refractive index (density gradients) of the specimen solutions to be measured.

John B Oct 22 2008