constant torque

are there any motors that are able to maintain a constant torque no matter the rpm . so say it runs at 5000 rpm no load and 5000 rpms under load because the torque doesnt decrease with speed increase or decrease and pulls the same amount of power

 

Read up on pulse width modulation. That is the technique used to maintain nearly constant torque over the whole range of DC motor speed.

AC motors can be controlled over a range of speeds with nearly constant torque using a variable frequency drive to essentially make a simulated AC waveform.

 

Power output is defined as torque times rotational speed. Since input power is proportional to output power, then at fixed RPM, the input power will change as the load changes.

 

you ask about motor with constant torque at variable speed or constant speed at variable torque?
if you mean constant speed (5000rpm at noload and 5000 rpm at loaded)
you should use syncronous motor which is AC-motor

 

my friend i believe that ,if there is load on synchronous motor then it draws more power,which is not desired .

 

I'm confused... Do you expect mechanical power for free? Of course the electrical power demand will increase! Synchronous AC motors do run at a fixed speed by design and will try its best to maintain it under load,.

Steve

 

alright thx for all the input

 

Every set of DC motor performance curves shows the torque going to zero at some speed. This is entirely different from the minimal torque required to keep a motor going at a constant speed within its range.