BRUSHLESS DC
Why should I choose a brushless motor over an ironless brush motor?
The are many factors that affect the decision to select a brushless motor for a particular application.
A brushless motor is often used when high reliability, long life and high speeds are required.
The bearings in a brushless motor usually become the only parts to wear out.
These bearings can last thousands of hours depending on shaft load and environmental conditions.
Often in a brush-type motor, the brushes and the commutator become the components determining the motor's life.
In applications where high speeds are required (usually above 30,000 RPM) a brushless motor is considered a better choice.
As motor speed increases so does the wear of the brushes.
Additionally, at higher and higher speeds it becomes increasingly more difficult to keep the brushes from bouncing on the commutator bars as they transition from segment to segment.
Thus, this brush bounce phenomena often becomes the practical limit of speed in a brush-type motor.
The mechanical switching of brushes on commutator segments often generate objectionable electrical and audible noise.
In these instances a brushless motor can usually sound quieter and provide less of a disturbance to other electrical equipment in the vicinity.
In applications where weight and/or size of the motor itself is limited, a brushless motor's commutation control can easily be separated and integrated into other required electronics, thereby improving the effective power-to-weight and/or power-to-volume ratio achievable by a conventional brush-type motor.
All these benefits have a cost.
A brushless motor package (motor and commutation controller) will usually cost more than a brush-type, yet the cost can often be made up in other advantages.
For example, in applications where sophisticated control of the motor's operation is required, the electronics necessary for a brush-type motor can typically end up costing about the same as the electronics required to control a brushless motor.
In these instances, a brushless motor clearly has the upper hand.
What wattage motors do your Brushless DC go up to?
From 24 watt to 600 watts
How fast do your Brushless DC go up to?
Most are variable speed with ranges from 400-4000 rpm while some models can run as high as 10,000 rpm.
STEPPER
1.8 degree or 0.9 degree?
Step accuracy is the primary character of a step motor.
Without step accuracy, the motor is useless.
Based on motor manufacturing capability, step accuracy is rated at +/- 5% of the full step.
That means a 1.8-degree motor would have step error of +/- 5.4 arc minutes, while 0.9-degree motor would have step error at +/- 2.7 arc minutes.
This is because the motor step accuracy is determined by the torque stiffness, and the torque stiffness is determined by maximum holding torque and the number of rotor teeth.
Motor torque function: T(θ) = To*Sin(Nθ)
Torque stiffness: dT(θ)/d = N*To*Cos(Nθ)
(where To=maximum holding torque,
N=number of rotor teeth,
θ=rotor displacement)
A 1.8-degree motor has a 50-tooth rotor and 0.9-degree motor has a 100-tooth rotor. With the same manufacturing capability, a 0.9-degree motor will have twice the step accuracy of a 1.8-degree motor.
40% more torque
The number of turns is doubled in bipolar mode and Ip equals 1/√2 of Ic when two coils are connected in series.
The torque is approximately proportional to the Amps times the turns. If the NI represents unipolar drive torque, then the 2N*(1/√2) I (=√2 NI) will represent the bipolar drive when coils connected in series. √2 are approximately 40% more than 1.
The number of turns is the same in bipolar mode and Ip equals √2 of Ic when two coils are connected in parallel. If the NI represents unipolar drive torque, then the N*√2 I (= √2 NI) will represent the bipolar drive when coils connected in parallel. √2 are approximately 40% more than 1.
Amps per coil vs. Amp per phase
If two sets of the coil are wound in each phase, and the motor is driven by a bipolar drive, the Amps per coil (Ic) & the Amps per phase (Ip) will be different, depending on the type of connection. Ip equals 1/√2 of Ic when the two sets of the coil are connected in series. Ip equals √2 of Ic when the two sets of the coil are connected in parallel. (See motor rating) Since only one set of the coil can be energized at a time with an unipolar drive, there are no differences between Amps per coil and Amps per phase.
Also, if there is only one set of coils being wound in each phase, there are no differences between Amps per coil and Amps per phase.
Electrical Phase
The number of electrical phases is defined as the number of independent winding coils being used.
Holding Torque vs. Dynamic Torque
Holding torque is the maximum restoring torque developed by the rotor when one or more phases of the motor are energized.
The dynamic torque is called running torque or pullout torque.
It varies at different speed by different driver technologies and power input.
As a rule of thumb, the maximum dynamic torque is about 70% of the holding torque.
Mechanical Angle & Electrical Angle
Mechanical angle represents the step angle of the step.
In the full step mode of a 1.8-degree motor, the mechanical angle is 1.8°.
In the 10 micro-stepping mode of a 1.8° motor, the mechanical angle is 0.18º.
An electrical angle is defined as 360° divided by the number of mechanical phases and the number of micro-stepping.
In the full step mode of a 1.8° motor, the electrical angle is 90°.
In the 10 micro-stepping mode of a 1.8° motor, the electrical angle is 9º.
Micro-stepping
Micro-stepping is used to increase a motor's step resolution.
This is achieved by controlling the motors phase current ratio.
It should be noted that micro-stepping does not increase step accuracy.
Micro-stepping will allow a motor to run smoother and with less noise.
The degree of the improvement depends on the step accuracy of the motor.
Unipolar vs. Bipolar
Unipolar - A unipolar driver's output current direction cannot be changed.
There are two sets of the coils for each phase in a motor.
Only one set of the coils can be energized at a time.
Each coil represents one phase.
Therefore, only 50% of the winding is utilized in the unipolar drive. The number of mechanical phases equals the number of electrical phases.
Due to the fact unipolar drivers only use 50% of the windings, the performance ranges from low to moderate.
The benefit of this is that it doesn't generate too much heat.
Bipolar - A bipolar driver's output current direction can be changed. 100% of the winding is utilized in the bipolar drive.
That means the two sets of the coils in each phase can be connected either in series or in parallel to become one set of a coil.
Current direction changed from the driver creates another mechanical phase.
The number of mechanical phases is always twice the number of electrical phases.
Bipolar drivers provide 40% more holding torque than unipolar drivers, but typically run at higher temperatures.
For this reason, proper heat dissipation is important with bipolar drivers.
What is a Step Motor?
A step motor is a motor which convert input pulses into proportional steps (position).
What voltage should I use?
WhaIn order to get the maximum output from a motor for a given application, we have to maximize the torque at the operating speed.
Over 1000 pps full step is not desirable if the power supply voltage is less than 12V. High power supply voltage (> 24V) would be necessary if operating speed is selected over 4000 pps full step is necessary.)
What is the minimum number of steps to get the best step accuracy?
When running in Full Step, run 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.
What are the advantages of using step motors?
1. Speed can be easily determined and controlled by remembering that speed equals steps per revolution divided by pulse rate.
2. A step motor can make fine incremental moves.
3. A step motor doesn't require encoder feed back (Open loop).
4. Non-cumulative positioning error.
5. Excellent low speed/high torque characteristics without gear reduction.
6. Holding torque of the step motor can be used to hold loads in stationary position without over heating.
7. Ability to operate on a wide speed range.
How can 4 wire, 6 wire and 8 wire motors be connected?
First of all two drivers exist Unipolar and Bipolar, Unipolar drives output to 6 leads of a step motor and Bipolar output to 4 leads of a step motor.
So a 4 lead motor can only be connected to a Bipolar driver.
A 6 lead and 8 lead motor can either be connected to a Unipolar driver and or a Bipolar driver.
A wiring diagram shows the possible connections.
How fast can I run my step motor?
Most stepper motors are designed for low speed (3000 rpm or less) operation. Once you get into higher speeds, servo motors are typically used.
