#Motor Physics.

This is a small iteration from the last level of detail.
The following are some motor physics.

So I researched some different types of motors.
For this application AC-drives are not suitable, they have a fixed speed or are very expensive.
We are then left with DC-motors, stepper and servo.
There are more types but these three are the most common in use.

### DC-motor
This is probably the most simple motor.
Feeding a current trough the motor gives a torque at the mechanical axis.
These motors rotate at a high velocity and often require a mechanical reduction.
They are cheap though.

The problem is in the control.
A constant current is required to compensate for any gravitational pull on the load.
Furthermore, there is no feedback on the system. Therefore, we need an angle sensor.
Adding to the complexity.

Another choice we have to make in the type of motor is the brushed or brushless.
But both options still require some elaborate control.

### Stepper
A steppermotor is a brushless DC motor that is split in a number of multiple equal steps.
Where a brushless DC would have 6 steps. A stepper motor can have 60 steps. or 120.
By applying voltage to the next step we can move the rotor a single step.
They run best up to 1200 RPM.
The torque they can deliver is dependent on the current speed.
The stall torque can be around the 0.2 Nm.
But that drops off at higher velocities.
[Stepper motor on Wikipedia](https://en.wikipedia.org/wiki/Stepper_motor)

### Servo
A servomotor is especially a motor with a build in controller.
Often the motor itself is a simple DC-motor with permanent magnets.
And then there is a angle sensor and a small feedback controller to control the position.
The angle is communicated by PWM signal. And the servo will do the rest of the work.
Although the servo is simpler to control, it is often more expensive to get a motor that is similar to the stepper.

## Decission.
From our earlier model I concluded that a velocity of 25 rad/s and a torque of 0.01 Nm is required.
This should be doable with a stepper motor.
Furthermore, the fixed position is a very nice option.
For now I will go with the Steppermotor. They are more affordable and above all have fairly decent datasheets.


## Current model state
This model does not yet implement a steppermotor implementation.
But it does implement simple DC motor.
For the next step it is important to have some controller that is better suited.

