If I understand correctly, torque is proportional to coil current, so theoretically you could get the desired torque at any speed as far as you can supply the desired current to the windings. Unfortunately, there are two reasons that is not possible:
1) the cycle time a coils is energized is reduced as rotational speed increases, this makes it more difficult to achieve the desired coil current, specially when you have a voltage limited power supply.
2) the rotation of the motor induces a an opposite voltage on the coils (counter electromotive force) that reduce the maximum current that go through the coils. That effect is more important the faster the rotation speed is, thus limiting the maximum speed the motor can reach.
So usually you are left with real motors, that achieve the maximum torque at low speeds, but with the proper control can keep a good torque value for higher speeds.
Still, given the fact that motor power is the product of torque times the rotational speed, it is easy to see that for a given power figure toque has to go down as speed goes up.
What you want to achieve is to set the maximum efficiency point at the desired maximum speed. The figure below shows a given motor behavior.
![BL24B28-04_NEW_HR.jpg]( "BL24B28-04_NEW_HR.jpg")
The maximum efficiency will happen when the relationship between the electrical power used and the mechanical power delivered is maximized. If you add turns to the coils you increase the torque at the expense of reducing the maxim speed.
1) the cycle time a coils is energized is reduced as rotational speed increases, this makes it more difficult to achieve the desired coil current, specially when you have a voltage limited power supply.
2) the rotation of the motor induces a an opposite voltage on the coils (counter electromotive force) that reduce the maximum current that go through the coils. That effect is more important the faster the rotation speed is, thus limiting the maximum speed the motor can reach.
So usually you are left with real motors, that achieve the maximum torque at low speeds, but with the proper control can keep a good torque value for higher speeds.
Still, given the fact that motor power is the product of torque times the rotational speed, it is easy to see that for a given power figure toque has to go down as speed goes up.
What you want to achieve is to set the maximum efficiency point at the desired maximum speed. The figure below shows a given motor behavior.
The maximum efficiency will happen when the relationship between the electrical power used and the mechanical power delivered is maximized. If you add turns to the coils you increase the torque at the expense of reducing the maxim speed.