BL and BLDC?

[15mgtar]

Guys what is the difference between brushless servo motor (BLS) and brushless dc motor (BLDC)? any basic tutorial where I can gain knowledge outthere?

[Al_The_Man]

There are basically two types of brushless motors apart from steppers, which are of course also brushless.
The two main types are DC brushless and AC, the construction of which are practically identical in that they both have three star connected stator windings, the difference comes in how the windings are commutated.
DCBL are called this due to the fact they have only two winding energized at any one time.
See http://users.tinyworld.co.uk/flecc/4...otor031102.swf
With AC sinusoidal type the windings are fed with a true 3 phase pattern, sinusoidal in nature. Sometimes referred to as Synchronous motor.
Al.

[15mgtar]

If you would care to take a look Al I've attached the pdf for BLS and BLDC motor they both are identical but why they call one brushless servo motor and the other one brushless dc motor?

[ihavenofish]

Originally Posted by 15mgtar If you would care to take a look Al I've attached the pdf for BLS and BLDC motor they both are identical but why they call one brushless servo motor and the other one brushless dc motor?

servos have encoders.

basically same motor configured for 2 different purposes. one would be good for an axis drive, the other for perhaps a spindle.

i think if im not mistaken, a bldc (brushless dc) motor is usually controlled by velocity. you tell it to go 5000rpm, and it attempts to keep it there. hence the use in spindles. ac brushless motors (as mentioned) are synchronous and often controlled by torque which is used in conjunction with encoders to precisely control rotation. also, again if im not out to lunch, a bldc motor cant "lock" like an ac brushless can.

so really, the difference is mostly in how you control them.

[wang]

Originally Posted by 15mgtar Guys what is the difference between brushless servo motor (BLS) and brushless dc motor (BLDC)? any basic tutorial where I can gain knowledge outthere?

The difference is that they direct encoder,servo motor can Precision positioning,It is better accuracy than the stepper(stepping) motor,it is also a very complicated controller,
Brushless motor can not be precise positioning,Positioning function is achieved by the controller,However, poor accuracy.
Brushless Motor include sensor and sensorless motor
brushless motor is the DC into motor
brushless servomotors including AC servo and DC servo .
From the price for the servo motor is very expensive.
My company specializing in the production of brushless motor and controller.
It is used in the homecnc\Micro-milling machine etc.

[15mgtar]

So servo motor= BLDC + encoder, and it's true when servo motor - encoder = BLDC?
If servos have encoders then why in the pdf catalogue they both seems to have encoders on the back of the motors?
I'm still confused.

btw I did my cnc mill with stepper, now I want to build my cnc router with either stepper or servo.

[Al_The_Man]

BLDC and AC sinusoidal refers to the technology the motor is commutated with, in order for any of these motors to act in a servo fashion, requires a feedback device, this need not necessarily be on the motor itself, for e.g. on the end of a ball screw or rack pinion etc.
You will see the reference to H1-H2, as Hall effect feedback devices, nowadays hall effect devices are rarely used, the equivalent optical tracks are commonly included on the encoder mounted on the motor itself.
On early motors the physical hall devices were mounted on the motor, whether a motor encoder was present or not.
Motors can be manufactured to a servo grade standard with or without feedback encoder, they become servo's when defined by the application, i.e. used in a closed loop feedback system.
In fact the definition of servo does not mean it has to be a motor, it can be a hydraulic cylinder with linear encoder and a servo valve.
Al.

[Herbertkabi]

Believe me that they often have no idea about what they are speaking when talking about ac or dc brushless motors. Sinusoidal or trapecoidal waveform - both dependes about controller - you can use or or. As well as sensored or sensorless - sensored motor you can drive with sensored or sensorless controller but sensored controller you can use with sensored motors only like sensorless motor you can drive with sensorless controller only - but is it trapecoid or sinus - your choice!
There are much more subs like iron core - ironless ... axial flux, outer ... inner rotor ... a lot of sub-categories.
AC or DC - how to call ... one loves mother, another takes doughter.
Common brushless servo motors, there you cant find any "secrets", there are nothing novelty when to compare with "normal" brushless motors. Some RC brushless motors for example are even more advanced, really high-tech, better balanced, uses much better materials(!!!) than most of common servo motors. Yes - servo motors costs much more ... Yes - some servo motors are really expensive because used cobalt alloy laminations .. but only somes, not all. Mostly the prices of servo motors are really "oversized".
Cheers,
Herbert

[wildwestpat]

Hi 15mgtar

Suggest you start by defining the requirement for both accuracy and speed and define your budget portion for the lead screw drives. By doing this it will indicate very strongly which is the right solution for your intended build.

The series of motors you have identified from Motion King are part of the same family. One has an encoder built in the other does not.

The encoder has 6 phases and this will define its rotational resolution (I think this means 360 degrees divided by 2 to the power 6 = 5.625 degrees resolution. Please check and perhapse Wang will help out or ask Motion King.)

The brushless motor has positional sensors bulit in in the form of the hall effect sensors but these are normally used to replace the brushes and act via suitable drive electronics to comutate the current in the three phase fixed winding. The rotor will be a permanent magnet. The comutation ( The brushes and comutator replacement) could be controled to alter the speed and compensate for load demand.

You could use either to drive a lead screw. However one has the shaft encoder builtin the other would require one. Do not consider a linear glass scale for the encoder unless you have the means to compensate for the problems introduced by the mechanical spring and lost motion . This sort of compensation is mega expensive or the operating speed is very very slow as the exact position is approached so slowly as not to incite resonance. I don't wish to get into a debate on resonance before anyone starts in on me for raising this!

The humble but very useful stepper has no feed potential and will lose steps if the torque / speed demands are too great. Steppers also have another nasty quirk in that the steps are not necessarily linear. This differs from manufacturer to manufacturer. The non linearity when microstepping is another source of error and again the manufacturers figures are needed.

On the accuracy fromt there are other issues with frame ridgidity - thermal expansion - leadscrew accuracy etc. You need to build a budget for accuracy having first decided what your work pices require. The accuracy will vary throughout the machines envelope and you need to define where your zero references are. The end of the travel on each axis may not be too sensible which is why many use the mid travel possition particularly with dove tail slides. Home brew frames have different ridgidity criteria and these need to be addressed in any accuracy budget.

Start to identify suitable software and drivers for these servo motors and compare prices with the available budget. The drivers need to interface to the software you are going to use to turn your code into cutting instructionsfor the machine.

Hope this helps you decide on the stepper - servo drive for your lead screws. I have always found it necessary to start from the accuracy of the work that is required and then to translate that tolerance back into the machine design. It is my experience this rapidly fixes the major variables alowing the designer to concentrate on honing the advantage of the obtainable parts. Whilst pipe dreams are good it is all too easy to get seduced by data sheets only to find that implimentation costs are unattractive or the required accuracy is not readily obtained.

Sorry this is long winded and a bit negative but cost and accuracy are not easily balanced.

Look forward to further postings as your design develops.

Regards

Pat

[Al_The_Man]

Originally Posted by wildwestpat The encoder has 6 phases and this will define its rotational resolution (I think this means 360 degrees divided by 2 to the power 6 = 5.625 degrees resolution. Please check and perhapse Wang will help out or ask Motion King.)

The motors are shown to be 3 phase 8 pole motors, if so, this implies 4 electrical revolutions/mechanical rotation of the shaft.
The wave forms shown indicate the commutation sequence per 1 Electrical 360° revolution.
Although it is technically wrong to indicate phases when the motor is used in a DC brushless fashion, in this case Winding should be used.
Al.

[15mgtar]

wow the info you guys given me is too much for me to understand. Maybe I just stick to stepper motor since atleast I know how to hook it up to the parallel port and setting in mach3. But I heard people would prefer servo nowadays then stepper.
one last thing pls help me about these 2 models on stepper driver I can not tell which is got more power to drive a big stepper motor. Pls see the attachedment below. They both got the same output.

I really appreciate you guys effort to help me.

[ihavenofish]

Originally Posted by 15mgtar wow the info you guys given me is too much for me to understand. Maybe I just stick to stepper motor since atleast I know how to hook it up to the parallel port and setting in mach3. But I heard people would prefer servo nowadays then stepper. one last thing pls help me about these 2 models on stepper driver I can not tell which is got more power to drive a big stepper motor. Pls see the attachedment below. They both got the same output. I really appreciate you guys effort to help me.

you need to know the motor specs to know what drive to use. "big" isnt a spec . you need to know the rated amps and inductance. from there you can figure out ideal voltage and decide if the amp will work.