[slow-poke]

Newbie here.

Preamble:

This is for hobby use not professional.

I have two manual mills, I converted one of them to CNC about 10 years ago using NEMA34 steppers and using Mach3 to control. I made a custom control panel it all works quite well and I'm quite happy with it. Only complaint is maximum speed, I'm using the original ACME lead-screws. This discussion is not about that conversion, only to give readers some idea of where I'm at with CNC type stuff.

I now want to convert my new (old 1989) 8 x 30 knee mill, I'm considering using servo motors this time. Not sure if I will use Mach3 again or something else, that's another discussion but do like the idea of using servo's with simple step and direction signals for drive.

I know someone that has converted a similar knee mill and he used Clearpath SDSK 3421S-RLS servos (NEMA 34, 289oz-in continous, 1100oz-in peak) directly driving the screws and he is quite happy with the performance.That servo sounds perfect specification wise, but are expensive for my hobby type requirements.

I have read that there are now more affordable (Ali-Express etc) servos, would appreciate any information/suggestions for these lower cost servos and suitable drivers that incorporate the feedback from the encoder.

Images (everyone likes pictures). Green is old, white is new.

[joeavaerage]

Hi,
yes there are a lot cheaper Chinese made servos, say a half or even less than Clearpath. I have no reason to suspect that they don't work, but they have anywhere from fair to atrociuos documentation, questionable
support and usually no setup and tuning software. If you've not used servos before you will want, if not need setup and tuning software. I understand you want good value for money and many of these
cheap servos are just that.....but.......they can be a PITA to get to work. There is a lot of parameters to program in a modern AC servo, do yourself a favour and get a brand with setup software.

I use use 750W Delta B2 servos. The complete kit (servo, drive and cables) costs $438USD plus shipping. I have bought four at this price in the last year. So they are not the cheapest, but they
have great documentation, good support and most importantly free setup and tuning software. Delta is a Taiwanese brand made in China. The shipping to New Zealand is $156USD for three day Fedex.
The record to date is two days, twenty hours and the slowest is four days and some hours(cant remember now?).

https://www.fasttobuy.com/flange-80m...er_p28084.html

Another brand that is likewise good quality and value is DMM, a Canadian brand made in China.

Both are good quality, support and value....but not the cheapest. A 750W Delta B2 is a little less than a 400W Clearparth....so twice the power for about $100 less.

Craig

[slow-poke]

joeaverage,

Thanks for that. I'm located in Canada so I should probably look at the DMM brand.

Anyone have experience with DMM servos?

[joeavaerage]

Hi,
they are highly regarded in the US and Canada and widely used.

The freight makes them too expensive here in New Zealand.

Craig

[slow-poke]

I contacted DMM, they want US$600 per axis, that would be CDN$3300 and that's more than I paid for the entire mill.


I did find T6 series ac servos at stepperonline https://www.omc-stepperonline.com/t6...ac-servo-motor

Certainly more affordable, not sure if I should get with brake, is that necessary?

The T6-RS750H2A3-M17S 2.39Nm sounds like it would be up for the task

Anyone using these T6 servos?

[joeavaerage]

Hi,

I paid $438USD plus $156USD shipping or $594USD per servo.....so $600 for DMM's sounds about right.
Remember you'll have these servos for twenty years or more. Your choice.

I bought one servo with a brake for use on my Z axis. To date the Z axis is not heavy enough that I truly need a brake, but I'm designing a new headstock which will
be cast in iron, and then I'll be fitting an ATC spindle. So, in the years to come the brake will be required, so I got it when I bought the servos. Cost an extra $150USD. This is an
example of the thinking 'I'll have these servos for twenty years'.

My servos too are 750W with 2.4Nm torque (cont). If geared correctly they should handle any reasonable load. The only time you really need sweat whether 750W is big enough
is if you want production speeds....then you might choose 2kW or bigger servos.

Plenty of people use T6's, they are cheap right? Do they have set up and tuning software? If they don't then I would not bother, not because they won't work, but that
you'll find it an uphill battle to set up, program and tune them without software assistance.

As an example of how simple it can, and should be: I spent quite some hours programming my first servo which was to be for the X axis. I had to learn the terminology, I had to experiment with
active high vs active low, I had to experiment to use Auto-tune.....all-in-all quite a learning curve. When I was happy with what I'd done and had it in the machine and tested it out I was
able to save the settings as a file on my PC. Thus, when I went to set up and tune my Y and Z axes, I could use that file as a template. As it turns out on my machine the X, Y, and Z axes are all very
similar, so programming the Y and Z axes took about a minute each. I have since bought two more servos for my fourth and fifth axis. There again I was able to use my file as a template,
all I really needed to change was the electronic gearing and following error settings, otherwise all the signaling as the same. About five minutes per servo.

If you have to program your drives by pressing buttons like on a microwave it will take hours to do each, and even more hours to fix the mistakes that inevitably creep in by doing it
that way.

Craig

[WesM]

I sent a PM about this but I will post here for anyone else looking, but the T6 servo is made by leadshine and use the leadshine tuning software. I will be going through the tunning process for my T6 servos in a few weeks and will post the results in a build log.

https://www.youtube.com/watch?v=FEPfznStd0s

Marco did a pretty good video on the leadshine software if you go to the tuning section.

DMM-tech sells a 3 axis kit on ebay at a discount if you decide to try them out.

https://www.ebay.com/itm/16464258895...424.m570.l5997

[joeavaerage]

Hi,
that DMM kit is for the DYN2 servo drives, ie 60VDC input whereas the DYN4 drives are 230VAC input, and cost a little more, back to OPs $600 each quote.

The bottom line is that good does not come cheap.

If you think DMM are expensive then take a look at Yaskawa or even worse Siemens!

Craig

[WesM]

You are correct Craig about the 60v system. Max RPM of the servos will be limited to 2k I think. Thats still good for around 300 IPM in a machine his size depending on the ballscrew pitch, I don't think you would want to ever run much faster then that on a non enclosed machine! The Mikron 5 axis machines I run at work can get to over 1000 IPM, I would be terrified to be around one of those without an enclosure.

Yeah I think we all get that there is ever more expensive options out there. Those of us doing this as a hobby on a limited budget will always be searching for the best value. Had I known the T6 servos were 220v +/-10% and my home power is 247v, I probably would not have gone the T6 route. I'm still nervous about hooking them up without a transformer. The delta servos you like were my other main contender.

[joeavaerage]

Hi,
my standard incoming AC power is 243V, and I hooked that to Delta servos no trouble. I think ANY 200V Class servo drive will work even up to 247VAC. 247AC rectifies to 349VDC (247 x square root of 2) . Whats the bet that the braking
resistor switches on at 380VDC or so. So the manufacturer fully expects the DCLink to climb to 380VDC under heavy deceleration, thus it should handle 349VDC no trouble.

I am a hobbyist too, and like you want cheap......but more importantly I NEED VALUE. Delta have a good reputation and a long standing in the market place, still a distant competitor
to Yaskawa no doubt, but better VALUE than Yaskawa. There have been any number of posts on this forum alone where some hapless servo newbie has bough a cheap Chinese servo and then struggled
like hell to get them going. I've seen those posts, and did not want to be one of those hapless servo newbies. So I paid a little extra to get Delta's. I could have paid say $300USD plus shipping for cheap
Chinese but I made $438USD for Delta's....an extra $138USD. That was my choice....not because I have any more money than anyone else, but I want and DEMAND VALUE....and that is what I got.
The more money I pay for something the more insistent I am that it does exactly what it supposed to. Servos fall into this category.

I've been using my new machine for just over two years now, and whatever I paid back when I bought them is well and truly in the rear view mirror now. What I have in front of me is some quality servos
that I fully expect another eighteen tears trouble free service yet. Over the service life of a servo a couple of hundred either way is nothing....twenty years trouble free is everything.

Craig

[WesM]

So I was recently tasked with researching a toolroom bedmill for the organization I work for. Among the competitors we are looking at is ProtoTRAK. I was at their showroom this morning and was surprised to hear they are using Delta AC servos in their machines. One of the other machines we are looking at is rotary surface grinders. And what do ya know, one of the brands we are looking at (dcm-tech) is also using Delta servos in their higher end product line. That definitely adds some credence to Craig's recommendations,

[joeavaerage]

Hi,
in the US Delta servos are marketed as SureServo.

To my mind there are three categories of servos, the el-cheapo Chinese made ones, then there are the better quality types of fair value, like Delta and DMM, and then there are the much more expensive
types, typically Japanese, US and European ranging up to Yaskawa and Siemens.

To my knowledge the Delta performs as well and has all the same features as the most expensive brands, but a lot cheaper....even if they are more than el-cheapo Chinese.

Craig

[slow-poke]

I thought I should provide an update on this servo selection thread I started now that I have selected and installed some of the servos.

I decided to take a chance with StepperOnline T6 ac servo. I ordered the T6 Series kit: 750W AC Servo Motor Kit 3000rpm 2.39Nm 17-Bit Encoder IP65, priced at $206
https://www.omc-stepperonline.com/t6-series-750w-ac-servo-motor-kit-3000rpm-2-39nm-17-bit-encoder-ip65-t6-rs750h2a3-m17s

Feel free to ask questions, here is the bullet point summary for those that are considering this route:

I can't speak to long term reliability. I can tell you the following:

+ Product comes as a package with motor, drive and cables
+ Product was shipped promptly and was well packed.
+ Quality of product appears to be very good.
+ Motor was fairly simple to tune
+ Very fast, powerful and near silent compared to the steppers I used in the past for CNC conversion of my old mill.

• Tech support is polite but not very helpful
• The mounting bolt spacing (90mm bolt hole circle) is smaller than NEMA34

- You need a 220V (not 240V!) source, so you will likely need a transformer, I found a suitable used one for $20, I think Wes found one for $50
- Would be wise to order the motor tuning cable to USB converter cable from StepperOnline
- Software and documentation do not match causing some confusion with software


This is a WIP, a couple images of present state...

[joeavaerage]

Hi,

- You need a 220V (not 240V!) source, so you will likely need a transformer, I found a suitable used one for $20, I think Wes found one for $50

No you don't. I use Delta servos which like most Chinese made products is rated for 220VAC, but I run them here is New Zealand where our single phase is 240VAC without a transformer
and have done for years. These devices are '200V Class' and will accommodate any reasonable single phase input from 200VAC to 250VAC.

Do you think it would make good sense for a manufacturer to produce a product destined to be exported all over the world that required a transformer???? No, in order to maximize sales
their device MUST be able to operate seamlessly on whatever the local supply is.

Craig

[slow-poke]

Hi,

No you don't. I use Delta servos which like most Chinese made products is rated for 220VAC, but I run them here is New Zealand where our single phase is 240VAC without a transformer
and have done for years. These devices are '200V Class' and will accommodate any reasonable single phase input from 200VAC to 250VAC.

Do you think it would make good sense for a manufacturer to produce a product destined to be exported all over the world that required a transformer???? No, in order to maximize sales
their device MUST be able to operate seamlessly on whatever the local supply is.

Craig

According to tech support, you should under no circumstances exceed the absolute maximum of 242V, and in fact the over voltage alarm in the drive will be triggered at that level. This is not a Delta servo, it's a StepperOnline which seems to be very similar to a Leasdshine E6.

Will it fail at the typical 245V we see daily on our 240V +/-6% system, probably not. Will it shorten the lifespan, probably. For the $20 cost of a buck transformer, I'm unwilling to risk burning up four drives running above the maximum voltage specification as provided by the manufacturer.

My understanding is that New Zealand nominal MAINS voltage is actually 230V
Quick look at a Delta 220V series driver and they show input voltage as 200-230V

FWIW, I'm an electrical engineer, worked for two power utilities and spent a good part of my career designing (really expensive electronic) equipment to test power systems that we sold to utilities all over the world. Do as you like but I'm not sure it's the best advice to lump all made in China drives as the same, because they are not. Some of these drives have a 400V bulk capacitor and some have 350V bulk capacitor. 240V + 6% = 254V, 254(sqrt2) = 360V, Really bad idea to run a large electrolytic beyond its rating like this for an extended period., FET's are likely to have a similar rating)

[joeavaerage]

Hi,
BS. The incoming AC supply is rectified and smoothed with capacitors, and is called the DC link voltage. For 220VAC input the DCLink voltage is 311.1VDC. For 240VAC the DCLink voltage
is 339.4VDC.

Whenever a servo decelerates it will generate back into the drive, causing the DCLink voltage to rise. If the deceleration is aggressive and the voltage gets over say 370VDC then an IGBT
turns the braking resistor on to limit that voltage. ALL AC servos work that way. So the peak voltage is determined by the deceleration of the servo and the threshold at which the braking resistor is
turned on....not the incoming AC supply.

If the T6 requires a transformer then I consider it suspect.

Craig

[WesM]

Craig, I think the question is if any of us are willing to risk burning a drive to test out your assertion. You are probably right, but $50 for a transformer is cheap peace of mind in this regard.

The other question in the back of my mind is if this drive was actually designed for international use. Its quite possible the drive is designed for use in CN and is being offered to international markets because an opportunity/need was seen for cheap AC servos. I know this was a problem early on with DMM tech servos and they had to adjust the DYN4 drives to work on 240v. There are several reports of the DYN4 drives being damaged when run on 245v ac.

[joeavaerage]

Hi,
I have been suppling and fitting Delta servo is NZ for about ten years now, and five 750W servos fitted to my machine. There is not a transformer on any of them,
and over that time zero failures. If DMM or whatever other manufacturer cannot design their products to tolerate local supply conditions that is a black mark against that manufacturer.

Years ago being able to design for and provide a measure of voltage tolerance was difficult as the semiconductors themselves were very expensive. Today 650V MOSFETS are dime a dozen,
and if you want extra certainty then use SiC MOSFETS. There is absolutely no excuse for any servo manufacturer having products that are sensitive to overvoltage.

Craig

[slow-poke]

Hi,
I have been suppling and fitting Delta servo is NZ for about ten years now, and five 750W servos fitted to my machine. There is not a transformer on any of them,
and over that time zero failures. If DMM or whatever other manufacturer cannot design their products to tolerate local supply conditions that is a black mark against that manufacturer.

Years ago being able to design for and provide a measure of voltage tolerance was difficult as the semiconductors themselves were very expensive. Today 650V MOSFETS are dime a dozen,
and if you want extra certainty then use SiC MOSFETS. There is absolutely no excuse for any servo manufacturer having products that are sensitive to overvoltage.

Craig

Craig,

For reliability we don't design to nominal voltages, we design to worst case, as stated the utility specified tolerance is 240V + 6% , resulting in 360Vdc, These drives have a 350V bulk capacitor. I completely agree 600V FET's are common as nails so are 400V capacitors. In all likelihood the Delta drivers have 600V FET's and 400V capacitors, IIRC the S.O. drives have a 350V capacitor! Furthermore the mains voltage in New Zealand is nominal 230V.

[joeavaerage]

Hi,

Furthermore the mains voltage in New Zealand is nominal 230V.

As of a few seconds ago the AC voltage was 240.2VAC right where I sit. 243VAC is the highest I've ever seen in NZ, at least under normal conditions.

If a manufacturer is using 350VDC capacitors then he is building down to a price rather than up to a standard.

Craig