Connecting two stepper motors together typically involves wiring them to a single stepper motor driver, utilizing either a series or parallel configuration. The choice between these methods depends on the specific requirements of your application, such as desired torque, speed, and the capabilities of your motor driver.
Understanding Stepper Motor Drivers
Stepper motor drivers are crucial components that translate control signals from a microcontroller into the precise current pulses needed to move a stepper motor. Most modern stepper drivers operate as constant current drivers, meaning they regulate the current flowing through the motor windings rather than the voltage. This is essential for achieving consistent torque and preventing motor overheating.
Methods for Connecting Multiple Stepper Motors
When wiring two stepper motors to a single driver, the primary goal is to ensure both motors receive adequate current for proper operation without exceeding the driver's capacity.
1. Series Wiring
In a series wiring configuration, the coils of the two stepper motors are connected end-to-end, forming a single continuous circuit for the driver's current. This means the same current flows through each motor coil.
How it Works:
For a standard two-phase stepper motor, each motor has two independent coils (A and B). When connecting two motors in series, you connect the A coil of the first motor to the A coil of the second, and similarly for the B coils, before connecting them to the driver's respective outputs.
- Current Distribution: The most significant advantage of series wiring with a constant current driver is that the full current set on the driver flows through each motor's coils. For instance, if RepRap motors rated at 2A and 1.1 ohms are used, and the driver is set to 2A, then each motor receives 2A. This results in more power (higher torque) per individual motor compared to a parallel setup where current is split.
- Voltage Requirements: Since the driver must push the set current through multiple coils in series, the total voltage drop across the combined coils increases. The driver must therefore be capable of supplying a higher voltage to maintain the target current.
Pros:
- Higher Torque per Motor: Each motor receives the full current from the driver, maximizing individual motor torque.
- Synchronized Movement: Motors tend to run more synchronously as they share the same current path.
- Reduced Current Ripple: Can sometimes lead to smoother operation.
Cons:
- Increased Voltage Requirement: The driver must supply a higher voltage, potentially twice that for a single motor, to achieve the desired current through both motors. Ensure your driver can handle this.
- Heat Generation in Driver: The driver may generate more heat due to the higher voltage output.
- Reduced Maximum Speed: The increased inductance of series-wired motors can limit the maximum step rate or speed that can be achieved without losing torque.
2. Parallel Wiring
In a parallel wiring configuration, the coils of both stepper motors are connected directly to the same outputs of the stepper motor driver. This means the same voltage is applied across each motor coil.
How it Works:
For a two-phase stepper motor, you connect both A coils together and then to the driver's A output, and both B coils together and then to the driver's B output.
- Current Distribution: The current supplied by the driver is split between the motors. If the driver is set to 2A, and two identical motors are connected in parallel, each motor will ideally receive approximately 1A (assuming equal current sharing). This means each motor will produce less individual torque than if it were receiving the full 2A.
- Voltage Requirements: The voltage requirement on the driver remains similar to driving a single motor, as the voltage is shared across the parallel branches.
Pros:
- Lower Voltage Requirement: The driver operates at a lower voltage compared to a series configuration, which can be advantageous if your power supply or driver has voltage limitations.
- Higher Potential Maximum Speed: The effective inductance is lower in parallel, which can allow for higher maximum step rates or speeds.
Cons:
- Lower Torque per Motor: The driver's current is split, meaning each motor receives less current and thus produces less torque. To achieve the same torque as a single motor, the driver's current rating would need to be doubled.
- Uneven Current Distribution: If the motors are not perfectly identical, or if there are slight differences in wiring resistance, the current might not split evenly, leading to one motor having slightly less torque or potentially overheating.
- Increased Current Requirement for Driver: The driver needs to supply the sum of the currents for all motors. If two 2A motors are in parallel, the driver must be capable of supplying 4A in total.
Series vs. Parallel: A Comparison
| Feature | Series Wiring | Parallel Wiring |
|---|---|---|
| Current per Motor | Full driver current (e.g., 2A for a 2A driver) | Driver current split (e.g., 1A for a 2A driver) |
| Torque per Motor | Higher | Lower |
| Driver Voltage | Higher (sum of motor voltages) | Lower (single motor voltage) |
| Driver Current | Equal to single motor's required current | Sum of all motor currents (e.g., 4A for two 2A motors) |
| Max Speed | Lower due to increased inductance | Higher due to reduced effective inductance |
| Complexity | Moderate | Moderate |
| Ideal For | Applications requiring maximum individual motor torque from a single driver, within driver voltage limits | Applications where lower individual torque is acceptable, or higher speeds are prioritized, given a high-current driver |
Practical Considerations and Best Practices
When connecting two stepper motors to a single driver, keep the following in mind:
- Driver Current Rating: Always ensure your stepper motor driver's maximum current output is sufficient for your chosen wiring method. For parallel, it must be able to supply the sum of the currents for all motors.
- Driver Voltage Rating: For series wiring, verify that your driver can supply the increased voltage required to push the target current through the combined resistance and inductance of the motors.
- Identical Motors: It is highly recommended to use identical stepper motors when connecting them to a single driver to ensure consistent performance and prevent uneven current distribution.
- Wiring Quality: Use appropriate wire gauges to minimize resistance and ensure reliable power delivery, especially for longer runs.
- Heat Management: Monitor the temperature of your motor driver and motors, especially during initial setup and testing. Ensure adequate cooling if necessary.
- Back EMF: Stepper motors generate back electromotive force (EMF) when rotating. The driver must overcome this, which contributes to the voltage requirements, especially at higher speeds.
By carefully considering these factors and understanding the implications of series versus parallel wiring, you can effectively connect two stepper motors to a single driver for your specific application.
