1. What is the difference between Unipolar and Bipolar motors?

A traditional unipolar wound motor has six lead wires. Each winding has a center tap. Unipolar wound motors are typically used in applications requiring high speed and high torque. A traditional bipolar wound motor has four lead wires. There is no center tap in each winding. Bipolar wound motors are typically used in applications required high torque at low speeds.

2. What is the difference between a closed loop stepper motor controller and an open loop stepper motor controller?

An open loop stepper motor controller, there is no feedback going from the motor to the controller, so the controller cannot make any necessary adjustments. This type of controller is effective when the motor is bearing a constant load at a consistent speed, in which case few if any adjustments will ever be necessary. In applications with a variable load or speed, a closed loop motor controller, where feedback is sent back to the controller for adjustments, may be preferable. When an open loop controller is suitable, it is often preferable, in part because of its low cost and lack of complexity.

3. Can I run a traditional six leaded motor as a bipolar winding configuration (four lead wires)?

Yes. A six lead wire motor is able to run in a unipolar or bipolar winding configuration. You will see similar torque and speed output from traditional a six lead wire motor run in a bipolar wound configuration as you would see from running a four lead wire motor.

4. Are linear motors difficult to integrate into a machine?

Yes. A six lead wire motor is able to run in a unipolar or bipolar winding configuration. You will see similar torque and speed output from traditional a six lead wire motor run in a bipolar wound configuration as you would see from running a four lead wire motor.

5. How can 4 wire, 6 wire and 8 wire motors be connected?

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.

6. How do I calculate the number of teeth and the available step angle?

Nt = 360º / (S x Np )
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

7. How fast can my stepper motor run?

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.

8. What is rated current? What is peak current?

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.

9. How do I find the relevant stepper motor?

To find the appropriate stepper motor for your application, primarily two important parameters are required that are provided to the motor. These are the torque that the motor should realize and the speed at which this torque should be reached. On the basis of the motor curves that are stored on the website for every motor, you can then select the suitable motor. Our motor assistant helps you find the right motor.

10. How is a stepper motor constructed?

Stepper motors are synchronous motors. The stepper motor is made up of a magnetic rotor and several spatially offset stator coils. In order to generate a magnetic field, a current flows through the coils. Reversing the current direction changes the polarity of the electrical magnetic field. If this takes place in a defined sequence, a rotating stator field results that follows the toothed permanent magnet of the rotor. The electrical pulses thus determine the speed of the rotary magnetic field and the rotor transforms these pulses into a mechanical rotary motion with a defined step angle.

The rotor of the motor is ball bearing mounted on both sides of the motor. It has no commutators or slip ring capsules which means the expected service life of a motor depends on the load that acts on the ball bearings. We state that our motors have a L10h service life of approx. 20,000 operating hours when they are operated with the nominal loads (see Datasheet).

11. What are the application advantages of stepper motors?

Stepper motors are digitally controlled and regulated drives that have achieved the highest level of acceptance and prevalence since the technology transition (from analog to digital technology and current software solutions) due to favorable prices with maximum service life and little control required.

a) PC+PLC-capable (directly controllable via PC, PLC and microprocessor).

The use of the PC at the lowest, decentralized machine levels has given the Plug & Drive motors the maximum level of productivity. Nanotec was the No. 1 supplier worldwide to fulfill the requirement for a compact, efficient and cost-effective drive system with an industrial Plug & Drive motor. Not only have the development, wiring and assembly costs of a complete drive unit been drastically reduced, the EMC compatibility and machine availability have been improved, and the commissioning and service also considerably simplified. Continuous further development of the options for customer-specific requirements allow new and close partnerships to grow constantly to the advantage of a better and more economical end product.

b) Speed stability

“No drop in speed when the load fluctuates”: The stepper motor fulfills this requirement like no other motor at no extra cost. Particularly for precise closed-loop speed, synchronization or ratio controls (e.g. in precision dispensing pumps), the stepper motor can reach higher and finer resolutions thanks to digital processing. The improvement in control, process and surface quality is not only a theoretical advantage.

c) Direct drive

Stepper motors have maximum torque in the lower speed range and the Nanotec microstep drives enable still acceptable concentricity properties up to approx. 2 rpm. Other motors often need gears for this purpose in order to fulfill the requested speed and force requirements. Direct drives reduce system costs and, at the same time, increase operational safety and life expectancy. Naturally, if the space available is limited or the external moments of inertia are high, gears are essential for power and force adjustment.

d) Avoiding damage to machines and injuries

The disadvantage sometimes referred to as the "loss of sync." where a motor is blocked can even be an advantage in some cases in light of constantly increasing safety requirements. Sliding clutches and overload clutches in order to meet prescribed safety requirements are not normally necessary in association with stepper motors.

e) Positioning accuracy

As well as minimum coastdown, stepper motors also have a minimum transient response because of the narrow step angle. Even without external linear or angular encoders, stepper motors are excellent at fulfilling speed and positioning tasks. The microstep changeover of the Nanotec final output stages can, in fact, further increase the accuracy or resolution at no extra cost. All Nanotec stepper motors are also available with competitively priced encoders for detecting any blockages as well as for closed-loop applications.

f) High stiffness without brake

Stepper motors have the maximum holding torque at a standstill and thus also offer high system rigidity. Because of this property, no external braking mechanism is necessary unless safety braking is required for the Z axis. Even for normal stopping, the stepper motor can be advantageous. When a servomotor is stationary, the closed-loop control must operate at full speed. The drive control oscillates with a slight back and forth around the selected null point. In most applications this is of no consequence. When positioning a mirror for a metrological task that deflects a laser beam, for example, this oscillation can however quickly become disruptive. On the other hand, the stepper motor would simply move to its position here and stay still.

g) Highly dynamic

Primarily in conjunction with the new dynamic closed loop SMCI .. positioning control as well as PD6.. Plug & Drive motors up to a speed of approx. 2000 rpm, stepper motors achieve higher dynamics and angular acceleration than servomotors due to the high number of contacts, the low rotor mass and the small air gap. This has a primarily favorable effect wherever small distances and movements must be positioned or reserved ultra fast and, at the same time, with an extremely small settling time or transient response such as required in semiconductor technology, optics and also in textile machinery and testing machines.

h) Easy controllability

Drive solutions using stepper motors can be realized very easily and cost-effectively because they can be realized in an open loop, i.e. without external encoders. In addition to the motor, the power electronics (drive) and an appropriate power supply are required. An external time base (PLC, PC or simple RC oscillator) can take on the speed or position. The clock pulse could be specified with a small additional board, even via an analog input (0-10V, 0-5V or +/-10V) or potentiometer, and hence would be controllable similar to a BLDC motor.

12. Which start/stop frequency is possible or advisable?

The max. possible start/stop frequency depends on the frictional load or frictional torque but principally on the inert external masses and is specified as fs at no-load operation of the motor in the torque characteristics. If a straight line is placed between fs and the max. torque, in this approach the possible start/stop speed can found very roughly at the intersection point of the torque and straight line where the acceleration torque Ma = J * a to the frictional torque must be added.

The recording of actual start/stop characteristics can only be incorporated through elaborate measurement results with different external inertial masses, which are then entered as a plurality of characteristics in the torque characteristics as parameters. As, on the other hand, the exact moments of inertia at the beginning of the project are often not yet available, we can determine the possible start frequencies experimentally in our laboratory with different inertial masses.

13. What material are the leadscrews and nuts made from?

Generally, the screws are rolled from 303 stainless and the nuts are made from self-lubricating polyacetal. Other materials are available on a custom basis. For screws we have used 316 stainless, aluminum and steel. For nuts we use our Kerkite material , PEEK, Ertalyte, and other custom materials to meet various environment and performance considerations.

14. The stepper motor seems to exhibit a lot of vibration in my application. What are some of the things I can do to correct it?

This could be resonance. In a Can-Stack motor the resonance range is 75 to 90 steps per second range and in the Hybrid motor within 140 to 200. Try starting your acceleration ramp at above these levels. Micro-stepping will also help through these ranges.

15. Explain the difference between the Captive , Non-captive, and external linear actuators?

The captive actuator has a built in anti-rotation mechanism through the use of a splined output shaft that allows it to extend and retract as a unit with no requirements for additional anti-rotation. The captive actuator is designed for shorter strokes.

The Non-captive actuator has a leadscrew going through the motor and has no reasonable stroke limits but must be attached to an assembly that will not rotate. This will then allow the leadscrew to extend and retract without rotating.

The External linear actuator uses a leadscrew and nut combination that extends out from the motor. Linear motion is created by the nut traversing back and forth as the leadscrew turns.

16. Does the leadscrew rotate on a non-captive linear actuator?

No. Once one end of the leadscrew is secured to a non-rotating assembly that needs to be moved, it will actuate back and forth without rotating. Non-captive linear actuators a designed for longer stroke applications.

17. What is the difference between a 4 wire and 6 wire stepper motor?

The 4 wire motor is a "bipolar" which means two coils. In its operation two coils are on at any given time and current is reversed in the coils to achieve rotation. The 6 wire motor is a "unipolar" device with four coils with the commons are tied together in each phase and brought out.

18. Can I run the linear actuator into a hard stop?

This is not recommended on the finer pitch resolutions due to the high forces generated which may cause lock-up. It is possible however under reduced power input.

19. If I use micro-stepping, will the accuracy of my system improve?

No, if may even get worse as the rotor is now resting between poles. To improve the accuracy an encoder is required.

The torque/force will be reduced by approximately be 20% to 30%

20. My stepper motor/actuator appears to get extremely hot when in the static or holding position. Is this normal?

With rated current as holding current, the motor/actuator will have a 75c degree rise. This is indeed very hot, but normal. The motor/actuator has a class B insulation system (130c degree) rating. To minimize the heat rise try reducing the holding current 0.25 times the rated current

21. What is the standard operating temperature range of the assemblies?

Our standard temperature range is 32F to 200F (0 to 90C). For applications where your temperature will be higher and lower than this, other materials are available to meet your requirements including Kerkite which can be used in a -50C to +150C temperature range