[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