Even though this bicycle has big wheels, the pedals are light and it goes fast!
The wheels are made thinner for competitive use to reduce the inertia, so they are light.
Inertia Load (Load Inertia)
It is the amount of force that tries to sustain the current operation status of an object. An object always has a load inertia. If the load inertia is large, a large torque is required during acceleration/deceleration. The magnitude of this torque is proportional to the magnitude of the load inertia and the magnitude of the acceleration, which is determined from the operating speed and acceleration time.
The inertia increases in proportion to the mass, right?
That's right. But that's not all.
What else was there to do...?
It grows in proportion to the square of the radius!
I see. So when I open the umbrella and try to rotate it, it feels heavier than when it is closed.
So, when selecting a motor, do you know how inertia affects?
Well, did I hear that it affects the acceleration/deceleration torque that occurs during start-up and deceleration?
That’s right. As the inertia increases, the acceleration/deceleration torque also increases in proportion to the inertia. Well, anything else?
…What was it again?
Come on Vex, study hard! You need to consider the permissible inertia and inertia ratio.
Oh, I see. In case of AC motors, I have to choose one so that the permissible inertia of the gearhead exceeds the inertia of the equipment (=load inertia), right? If the load inertia is larger, the gear can't withstand it and it will break.
Last week, when Vex was spinning the umbrella, the umbrella shaft broke because it could not withstand the acceleration/deceleration torque of the inertia. Then how about using stepper motors?
For a stepper motor, the ratio of the load inertia to the rotor inertia of the motor is calculated by "inertia ratio = load inertia ÷ rotor inertia," and the motor is selected so that the inertia ratio max. 30 times (it is also 30 times max. in the case of αSTEP), right? But why do we need to consider the inertia ratio?
Even if there is sufficient acceleration/deceleration torque, if the inertia ratio is too large, the motor may not able to keep up with the acceleration command and may misstep.
You choose servo motors and brushless speed control motors so that the permissible inertia (applicable load inertia) exceeds the load inertia.
Good idea. If the permissible inertia (applicable load inertia) is exceeded, proper control becomes impossible and operation becomes unstable or stops with an alarm output.
Even if the load inertia is large, it could be driven by a small motor by reducing the speed with a gearhead.
The engine is finally starting to work. If you use the formula "permissible inertia (applicable load inertia) × gear ratio 2," something as large as the square of the gear ratio can be driven. If you decelerate the gears of Vex's bike by half, you can carry 4 times as much stuff with a gear ratio of 2. I wonder if you could load my luggage too!
Then the speed will be half, right? I don't want that to happen...
Updated with the latest information on March 12, 2021.
