Help Buying Servo and serv drivers

[axis_control]

Hi,

I am currently building a cnc lathe and earlier opted for steppers due to the cost factor. Later I discovered that some of the servo motors and drivers cost just a little bit more than the price of a stepper system.

Weighing both systems positive and negative points I find servos are a better option.
1] Steppers draw continuously the same amount of current irrespective of their working where as Servos draw current in proportion to their working. That makes a huge difference in the amount of electricity consumed.
2] Servos are precise in position (I do not know if any of the servos have failed to maintain position under their max stated load). Where as steppers have a fixed incremental angle for every pulse, though a single step can be done in to micro steps, but at the end it is still a min-max distance and not to the exact point.

So what I am looking to buy are 3 servo motors and compatible servo drivers for it. I require servos that are close to the Nema23 stepper motor range or a bit higher can do but not lower that that.

I earlier have bought a Nema 23 motor for the cnc, but I want to bail out of steppers and use servos.

I know there are few manufacturers of servos and drivers out there, but who has reliable products?

[mactec54]

axis_control

What you are looking for, you can get from Dmm technologys, They are the best low cost AC servos, & very easy to set up

Motion Control Products - DMM Technology

[axis_control]

Originally Posted by mactec54 axis_control What you are looking for, you can get from Dmm technologys, They are the best low cost AC servos, & very easy to set up Motion Control Products - DMM Technology

Thanks mactec54 for the help. They indeed are close to reasonably priced. I said close to because there are some Chinese servos and drives available that are cheaper than that, but those scare me ...lol [Edit :- I think it would be wrong on my part to weigh servos based on their cost. I came to this conclusion because I have been reading an article that explains the details of servo system like its complexities, Resolution in servos etc. I am sure every manufacturer out there has a certain specific resolution for their servo system.]

I guess you are using one of the DMM servos in your cnc.In case you are using them , I would like to know how they are performing

[axis_control]

My question is for Al the Man,
I think you can best answer my query since I have received help from you earlier and I have seen many benefit from your help

1] The way in which a stepper motor precision is measured, is in step angle. (how precise steps can it give under load)

2] The same way how can one define the precision of a servo motor? (Mathematically)

3] When I want to buy a servo, what questions should I ask the manufacturer or seller about the servo motor that will distinguish its quality?

[mactec54]

axis_control

Do you have the link to the Chinese servos & drives This I would like to see

The Chinese servos and drives available that are cheaper than that, but those scare me ...lol

[axis_control]

Originally Posted by mactec54 axis_control Do you have the link to the Chinese servos & drives This I would like to see The Chinese servos and drives available that are cheaper than that, but those scare me ...lol

I had found it on Alibaba.com a while ago. The person had quoted a servo motor for USD $125 and drivers somewhere close to that. I will try to find a link for the company as I had this conversation on Alibaba websites online chat.

Since you have asked that question, I have a feeling that I must have mistaken the DMM servo price due to my incomplete knowledge about the technology. While I was surfing through some of the information pages on servo system, I realized that there are resolution in servos too, now that`s what I did not know. Now if there is a question of precision in the technology then comparing them on price would be wrong, that`s what I have learn`t few minutes back.

[axis_control]

Originally Posted by mactec54 axis_control Do you have the link to the Chinese servos & drives This I would like to see The Chinese servos and drives available that are cheaper than that, but those scare me ...lol

I do not know if this was the exact same company I had spoken to.

400w motor servo nema24 products, buy 400w motor servo nema24 products from alibaba.com

[mactec54]

axis_control

The motor looks good, But has no spec on the encoder, this is the important part, there are lots of servo motors that are good like this one, but most are very limited because of the low encoder resolution

[axis_control]

Originally Posted by mactec54 axis_control The motor looks good, But has no spec on the encoder, this is the important part,

Now that is one very important part you have stated.

The encoder resolution is given in Bits. So how do I understand that so and so Bits is good and will suit my application.

I have no base to distinguish or understand this (Bits) because I have not dealt with software or electronics in a deeper way. A simple example would be the International system of weights and measures.When you want to compare something in the unit of weight (Metric system), then you compare it with the 1kg weight stated by International system of weights and measures. This makes it easy for you to understand the weight you are measuring. So in the same way how do I understand bits by comparing them?

[Al_The_Man]

The resolution of a stepper is simply the amount of steps/rev.
With a servo it will depend on the encoder resolution.
If you have a encoder with the resolution in bits, it is most likely a absolute encoder, not differential.
Also some serial encoders are listed in bits.
Both absolute and serial require a special form of decoding on the receiving end.
With a differential encoder, most controls or intelligent drives will multiply the quadrature pulse x4 rather than use one of the quad pulse native resolution.
Al.

Al.

[axis_control]

Originally Posted by Al_The_Man Both absolute and serial require a special form of decoding on the receiving end. Al. Al.

Thanks for replying

So does the special form of decoding limit one to buy a servo and the Drivers from a single manufacturer? What if one buys a servo from one and the Drivers for the servo from another manufacturer? Would this lead to problem due to possibilities of driver hardware not matching encoder out put?

(I would avoid buying servo and drivers from different places, but just out of technical query I though of asking)

[mactec54]

axis_control

Yes this can be a problem,Most brand name Drives motors (Like Yaskawa Etc) drives are matched to the servo motor & encoder, Some you can use a smaller motor like 400w with a 1000w drive of the same brand, always go for the higher encoder count per/rev Like 16384 14bit & higher, for a smoother running system