Motor requirements fall into two general categories; 1) the load requirement and 2) the environmental requirements. Frequently it is the latter, the environmental requirements, that create problems.
Load requirements can usually be dealt with based on a few primary parameters; speed, torque and duty cycle. Speed and torque are pretty obvious. he duty cycle component is more subtle and motor manufacturers incorporate thermodynamic calculations directly into their sizing programs. Basically it boils down to how long the motor is on and how long it is off. This is an attempt to deal with the ultimate limit of performance, the thermal equilibrium of the motor. Once the system reaches it’s maximum temperature, there is no more power to be had. Conversely, with low duty cycles it is possible to generate enormous peak power levels as long as there is time to get rid of the heat. This is why motors are often fan cooled. In recent years many suppliers are using forced air cooling and even water cooling to create more power in packages with fixed size.
The ultimate limit in electric motors is the insulation system itself. This has lead to increasingly high temperature insulation products like the polyimide resins of recent years. In permanent magnet motors, the high temperature insulation can cause gradual degrading of the magnets which will reduce the motor’s output over time. The tricky part of this problem is that you can’t tell. There is no inexpensive way to directly measure torque on an axis of a machine to check for torque roll-off. So we design ever more complex control algorithms in the motor control circuit to prevent such overheating from occurring.
On the environmental side, things get a lot more complicated. Every major industry has unique requirements that put significant design constraints on motor construction. Down hole Oil & Gas applications require that the motor be immune to extraordinary pressures from water ingress, high temperature operation and a host of issues from physical packaging issues that are problematic at best. Aerospace, semiconductor, automotive, oil and gas and food industry machinery all have requirements that make applying electric motors a challenge for all of the unique requirements that these industries require.
The list of special requirements is endless. And, in part, it is this aspect that makes it difficult for manufacturers to maintain volume production and address custom requirements at the same time. It remains a major issue to balance the constraints of motor design and application requirements with cost effectiveness. And it is these unique opportunities that will drive new motor and drive technology in coming years.