The original system employed the use of the Greartisan 12V brushed motor rated at 100rpm. The system was designed to have an input crank link with a D-shaft cutout matching the motor shaft's cross section profile itself.
The motor is rated at 12V and 1.1A, and so the theoretical max power is given by P = VI, or about 13.2W. At 100rpm, by using the relation of P = Tω and rearranging, the no load motor torque at 100rpm is 1.2605 Nm. The images below describe the motor visually and by specification..
Greartisan 12V brushed motor image and specifications
...
Therefore, it would be mechanically preferable to lower the angular velocity by at least half or more of the rated RPM. 30RPM would be optimal. The reduction of torque can also improve mitigate damage to the system. The simplest way to do is with the L298N H-Bridge motor driver. The working principle relies on Pulse Width Modulation, which reduces the average power by switching on and off an electrical signal (thus creating a discretized and modulated sequence of pulses). The L298N modulated voltage signals to reduce the average power. Its versatility lies in ease of implementation and adjustability to find a stable RPM and power figure rather than implementing a potentiometer and turning an analog dial for a rough approximation. In addition, the L298N interfaces easily with the provided Arduino UNO microcontroller and the H-bridge enables the motor to be spun clockwise or counterclockwise with a simple change in code.
High to
L298N H bridge Bridge Motor Driver
Circuit Schematic of DC motorMotor, 9V batteryBattery, L298N and Arduino UNO microcontrollerCicrocontroller, adapted from
https://www.instructables.com/How-to-Use-L298n-to-Control-Dc-Motor-With-Arduino/
Completed circuitCircuit
The following code allows for speed control by PWM (pin 9) and direction control (pins 2 and 3, simply swap HIGH and LOW) to flip direction
...