Is there an electric motor type which gives torque at low current

[Circlotron]

Ok, the title isn't long enough to properly ask what this thread is about so...

Is there any type of electric motor which, unlike the usual scenario, can give a large holding torque with minimal current requirements and then consumes power primarily as a consequence of providing higher speeds?

Brake motors exist.
electromagnetic actuator holds off the shaft mounted disc brake whilst the motor is being powered, and locks them when unpowered.

Simples!

X

I was going to say the same thing.
Automatic sliding doors for example often use a DC motor about the size of a drink can that has an electromagnetic lock. A disk rotates with the motor shaft and is pulled against a flat surface when the lock is energised. Similar in principle to the pulley on an automotive air conditioner compressor. If the two mating surfaces are sufficiently flat, quite a low power input gives a suprisingly strong grip.

[Doctorandus_P]

Torque itself does not need power (you can deliver constant torque with a spring) but generating torque though electrical ways will need current and thus power (ignoring superconductors)

It's the same difference as a flying helicopter, versus a load suspended from a crane. The crane machinist can turn off the crane and go on a lunch break and the load will still be suspended on the hook when he comes back, but the helicopter will fall out of the air if it's pilot goes for a lunchbreak. Without a mechanical connection you need power input to sustain the force.

And an electrical motor delivering torqe at stand still, does not disspate energy in the magnetic field (except for the first creation of that magnetic field). The energy is lost (heat generated) by the current carrying copper wire, it's just the copper resistance. With superconducting magnets you could create a constant torque in the motor without inputting constant engergy. Very similar to levitating trains in a magnetic field.

[johansen]

Ok, the title isn't long enough to properly ask what this thread is about so...

Is there any type of electric motor which, unlike the usual scenario, can give a large holding torque with minimal current requirements and then consumes power primarily as a consequence of providing higher speeds?

stepper motors are typically two rotor cores of 50 poles 180 degrees out of phase, with the 4 coils 90 degrees out of phase which each other such that only one coil is in phase with maximum coupling at any one time, giving 200 steps. they are designed to have minimal natural cogging torque without current applied, so that the error (when driven with two sine waves) is only 3% or so of one step. this is why anything more than 10 microsteps is a wash.

if instead you make the rotor in phase, not interleaved... what you'll get is a tremendous cogging torque, but you can still drag the rotor around by pushing on it with the coils.

this sounds like what Tim tried to describe as a pre biased stepper motor.

you can make what you describe by building a 12 pole 36 slot motor and winding a traditional 3 phase winding.. but the difference is you size the magnets to make maximal cogging torque. so, saturation, lots of it.. and 36 square block magnets exactly sized to the width of the poles in the motor.

[Marco]

Electrostatic motors have holding torque without active power.

PS. it has increments just like a stepper obviously, but a charged capacitor has no copper losses.

[BeBuLamar]

So the common way to have strong holding torque without power is to use a mchanical brake. In fact most of these brakes are spring loaded and they always brake. When you run the motor you much supply power to the brake to release it.

[Infraviolet]

That electrostatic motor idea is a most interesting idea. I'll have to read up on it and see whether there's any plausible hope of being able to build a lower performance DIY version.

[Smokey]

Current = torque.  No way around that.  It's magnetic fields and stuff. 
If you need to hold position without current, add a brake. 

[Doctorandus_P]

Current = torque.  No way around that.  It's magnetic fields and stuff. 

Well, there is a way around that. As mentioned a few posts back, you can use electric fields instead of magnetic fields.

[Smokey]

Current = torque.  No way around that.  It's magnetic fields and stuff. 

Well, there is a way around that. As mentioned a few posts back, you can use electric fields instead of magnetic fields.

Sure.  You could add hydraulic motors to the list too I guess. 

[Siwastaja]

Current = torque.  No way around that.  It's magnetic fields and stuff. 

Well, there is a way around that. As mentioned a few posts back, you can use electric fields instead of magnetic fields.

Sure.  You could add hydraulic motors to the list too I guess.

Or mechanical brake.

One thing people usually miss in threads like that is, with zero speed there is zero work done, which means zero output power, therefore zero input power does not violate any laws of physics. A mechanical brake is an easy demonstration of this. Or a worm gear.

[Doctorandus_P]

I did not miss that you can apply torque to a brake, but this thread is about motors. And beides, mechanical brakes had already been mentioned a few posts back.

I'm not sure if Piezo motors have already been mentioned. They are also much like a mechanical brake (high holding torque at no RPM and no power input) but they are real motors, they can move, although very slowly.