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Glossary
A stepper motor's rated current is the maximum current that the motor is designed to handle safely. This parameter is typically provided in the motor's datasheet by the manufacturer, and is crucial for ensuring safe operation and achieving maximum torque. If you want to operate the motor at lower temperatures, consume less power, or avoid the general risks associated with running a system at its limit, you can run the motor at smaller currents. This will still allow the motor to operate, but with reduced torque and speed. Do not, however, exceed the rated current as it can cause the motor to overheat and potentially suffer damage. The motor could even cause burns or cause plastic parts in its vicinity to melt. While it's normal for a motor to feel warm during operation, it should not become so hot that it's uncomfortable or even painful to touch. Thus, when configuring the motor, always start at the lower end of the current scale and err on the safe side!
The RMS (root mean square) current of a stepper motor is a measure of the average current that the motor draws during operation. It takes into account the fact that the current drawn by the motor varies as it steps. With a microstepping driver (as used in the Bpod Stepper Module) the current fluctuations resemble a sine wave and the motor's maximum RMS current can be calculated by dividing the rated current by the square-root of two (i.e., approximately 70% of the rated current):
The current flow through the coils of a stepper motor is controlled by the driver. A stepper motor can operate at a range of voltages, as long as the driver is able to provide the necessary current to achieve the desired performance. A motor's nominal, or rated voltage is derived through Ohm's law:
This, however, is not the maximum voltage you can drive the motor at. When selecting the driver supply voltage, keep in mind that a higher voltage will decrease the rise time of the coil current, resulting in greater torque at higher velocities. The motor's torque diagrams are typically based on a specific supply voltage, but you can adjust the velocity axis in proportion to the supply voltage to adapt the curve. For example, if the curve is based on a 48V supply voltage and you plan to operate at 24V, you can halve all values on the x-axis to estimate the motor's performance. As a rule of thumb use between 4 and 22 times the rated voltage as a supply voltage (a typical value being eight times the rated voltage). The Bpod Stepper Module is rated for a supply voltage of 5.5V to 24V.
It is important to note that these guidelines should be used with caution. The actual safe parameters for a stepper motor may depend on a variety of factors, such as the ambient temperature, cooling conditions, and the duty cycle of the motor. It's always a good idea to consult the manufacturer's recommendations or seek expert advice if you're unsure about the safe operating conditions for your motor.
Furthermore, remember that a stepper motor has the ability to generate a substantial amount of mechanical force which may pose a risk of injury or even death to humans or animals. Therefore, it is crucial to properly scale the motor and its parameters based on the specific requirements and to implement appropriate safety measures such as emergency shutdown and end switches.
The authors of the Bpod Stepper Module will not be liable for any damages arising from its use, even if advised of the possibility of such damages. Please refer to section 16 of the GPLv3 for details.