Motor:

For the motor, in the beginning I wanted to use a stepper motor with a controller, but after some experiments, I figured out that the stepper would give me a pretty nice accuracy in measuring the steps and would have a good torque, but it would not have a good speed for the tattooing process. So after some experiments and Stepper Motor tutorials for ESP32, I decided in the end I would use a small DC motor.

Since I wanted to be able to control the speed of it, but the PMW pins of the ESP32 would not give me enough amps, I had to add a mosfet module so I could also have an external 9v Battery as the Power Source.

The DC motor has a very good speed, but now the problem is that it does not has much torque, so I have to be pretty careful of any additional friction that could be generated because that would probably stop the motor, force it or overheat the system.

This means that in a system (without any friction) the relation of speed between the motor and the tattooing tip would be something like this:

MOTOR RPMS:     16.000RPM

MOTOR GEAR:      8 teeth
ARMS GEARS:      15 teeth

16000 RPM * 8 = y * 15

y = (16000*8)/15

y = 8533 RPM

This means that without any friction, the nail will pinch you 8500 times per minute... something like 142 times per second!!!

(But the truth is that it has a lot of friction, so it moves a lot fewer times per second).