Rotary Hybrid Stepper Motors FAQs

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NPM's stepper motors are available with either 2-coil Bipolar, or 4-coil unipolar windings. Bipolar motors have 4 leads, while unipolar motors have 6 leads. Additionally, some motors are designed with eight leads, so they may be connected in a variety of ways.

Connection Instructions

Fig 1a. PF/PFC/PFCL series (Tin-can type) Bipolar

Fig 1b. PF/PFC/PFCL series (Tin-can type) Unipolar

Fig 3a. PR series (Hybrid type) Bipolar

Fig 3a. PR series (Hybrid type) Bipolar

A 4 lead motor can only be connected to a Bipolar driver. The 6-lead and 8-lead motor can be connected to either a Unipolar driver and or a Bipolar driver. A wiring diagram shows the possible connections.

An encoder will send output signals for decoding. These decoded signals will relay current speed, position, and will verify if a motor is missing steps. After comparing input pulses to output steps, corrections will be made.

Most hybrid motors current controlled driven (PMW/chopping drives) as opposed to voltage-based drives. If a motor is rated at 5V, the output current must be limited in order to keep the voltage across the coils under 5V. Stepper motors typically have a current label because they are usually current driven.

Nt = 360º / (S x Np )
or
S  = 360º / (Nt x Np )
Nt = Number of rotor teeth (must be an integer)
S  = Full step angle
Np = Number of mechanical phases (must be an integer)
      = Number of full steps to repeat the same mechanical line up
         between the stator tooth and the rotor tooth
Np = 4 for 2-phase bipolar motor
      = 10 for 5-phase bipolar motor
      = 3 for 3-phase unipolar motor

Use a multimeter to check the resistance of each phase. Check between Phase A and /A and then between B and /B. Check the data sheet provided to ensure there is no more than a 10% difference. This operation is necessary when too much current or voltage is applied to the motor.

Step accuracy is inherent in a motor's mechanical design and is controlled by the torque stiffness. Microstepping increases the step resolution, but not the step accuracy. Micro-stepping a motor without good step accuracy will not provide the smoothest motion.

Most hybrid stepper motors are able to operate around 2000rpm or less. Remember that in higher speed, the torque will be lower than when the motor is in a lower speed. Once you get into higher speeds with torque, servomotors are typically used.

Steps per revolution equals 360° divided by step angle (0.9°, 1.8°, 3.75°, 7.5° and 15°).

• 0.9° = 400 steps/rev
• 7.5° = 48 steps/rev
• 1.8° = 200 steps/rev
• 15° = 24 steps/rev

These numbers are when the motors are driven in full-step excitation mode.

The current rating of a stepper motor is based on heat dissipation (Watt=I^2xR) of the motor. A larger motor dissipates more heat than a smaller motor. With the same phase resistance, a larger motor has a higher current rating than that of a smaller motor. A motor mounted in a good conductor will also result in more heat dissipation than that of one mounted on a non-conductor.

There are several advantages of using stepper motors. Speed can easily be determined and controlled by remembering speed equals steps per revolution divided by pulse rate. Stepper motors can also make fine incremental moves and do not require a feedback encoder (open loop). Stepper motors also have fast acceleration capability and have non-cumulative positioning error. Along with excellent low speed/high torque characteristics without gear reduction, stepper motors can also be used to hold loads in a stationary position without creating overheating. All stepper motors have the ability to operate on a wide speed range.

It is a motor that uses input pulses to take proportional steps. These motors can be used for positioning and/or speed control in various applications. To change phases, steppers require power and sequence circuits.

Microstepping is used to increase a motor’s resolution. This is achieved by controlling the phase current ratio. Microstepping does not increase step accuracy, but will allow a motor to run with less noise and smoother. The degree of the improvement depends on the step accuracy of the motor.

The rated current is what the motor is rated at. The peak current refers to the amount of current the driver outputs.

Non-microstepping drivers
Peak Current = Rated Current

When using a driver that only does full stepping, the rated current is the same as the peak current. (Rated current = Peak Current).

Microstepping Drivers
Peak Current = 1.4 x Rated Current

When using a driver that is capable of doing microstepping (microstepping = 1/2, 1/4 stepping or more), the definition of peak current becomes 1.4 times the rated current. Microstepping drivers are made differently in order to maximize their ability to drive the stepper motor. Therefore, step motors can handle up to their rated current multiplied by 1.4. (Peak Current = 1.4 x Rated Current). This will not damage the motor because the power output is more or less the same.

To determine a motor’s resonance, take the square root of (torque stiffness divided by total inertia). Although resonance frequency cannot be completed eliminated, it can be changed by altering the rotor or system inertia or by altering the torque stiffness.

This refers to a six-lead motor (unipolar step motors) when a bipolar drive is being used to run the motors. Since bipolar motors only need four wires to run, there are options in connecting a six-lead wire to a bipolar drive. Typically, we refer to the six wires as A, /A, A Common, B, /B, B Common. Half-coil connection would be to use A, A Common, and B, B Common (or /A, A Common, and /B, B Common). To use full-coil, also known as series connection, you would use A, /A and B, /B. For full-coil the two common wires are ignored. The full-coil connection (or series) is ideal for lower speeds requiring more torque. The half-coil connection will give an overall amount of torque across a wider range of speeds.

Holding torque is the maximum restoring torque developed by the rotor when one or more phases of the motor are energized. The output torque is also known as running or dynamic torque. Output torque varies at different speeds with different drivers and power input. In general, maximum output torque is 70% of the holding torque.

Mechanical angle represents the step-angle of the motor. In using the full-step mode of a 1.8° motor, the mechanical angle is 1.8°. The electrical angle is 1/16^th of the mechanical angle. Thus the electrical angle of a 1.8° motor is 0.1125°.

When running in Full Step, run the motor in increments of 4 steps. This way, the motor will end in the ‘A’ position every time, which is the rotor’s natural position.

When using a hybrid motor, NPA does not recommend using either a L/R or voltage drive. These drives, which provide constant voltage, create heat during operation and as a result will increase the motor’s resistance. Any change to the motor’s resistance will change the current supplied. NPA recommends using a constant current drive, such as PWM/chopper drive, for all applications with hybrid motors. When using tin-can motors, these limits do not apply.

No. A stepper motor does not draw any increased current when in a stalled position.