## 2012年5月10日 星期四

### High-inertia motor is not always better and the low-inertia motor is not always worse. It depends on application.

1. High-inertia motor is not always better and the low-inertia motor is not always worse. It depends on application.
T= I x α (Torque = Inertia x Angular Acceleration)
P= T x ω (Power Rating = Torque x Angular Acceleration)
P = I x α x ω
Therefore, with the same power, if the inertia is increased, the acceleration must be decreased which means the characteristics of the acceleration and deceleration are worse. Of course, the angular speed will be changed, too. Here, we assume that the operating speed remains the same.
“I “ is a fixed value. After a system (such as flying shear system, the flying shear will not change. But if it is used for conveyer belt, the inertia will change. When the goods on the belt become more, the drag force should be strengthened.) is set, the users can use the formula (T=I*α) to estimate the acceleration and deceleration, and the required torque.
α = (target speed- initial speed)/ (needed time from initial speed to target speed)
If a system needs the torque of 1 N-m, and using either high-inertia or low-inertia motor is able to achieve the performance, the low-inertia motor is a better choice if a quick response and a high speed are desired.
Therefore, it can be easy to explain why low-inertia motor is better by the above formula. Because the rotor inertia of the low-inertia motor is lower and the rotor is lighter also, so when the motor stops, the regenerative power will be less. By the same logic, hitting the wall at the same speed, the power of the fat person is bigger than the thin person’s.
In conclusion, if the application requires quick response and good acceleration and deceleration characteristics, the low-inertia motor is more applicable (if the torque force is enough). If the application needs large torque, such as heavy lifting system, the high-inertia motor would be more suitable.