NordicCNC's build log

[NordicCnc]

A JMC 180W might be enough power wise, but industrial servos are much more sophisticated. Encoder resolution, motion smoothing (much needed for high accel when the controller doesn't handle S-curve motion profiles), vibration suppression, ...
To be honest I also had a different machine in mind from what you're planning when you stated your requirements :)

For calculating the required motor, I simply plugged the numbers in Yaskawa's calculator (SigmaSelect).
It's a 2005 ballscrew coupled with 1:1 pulleys (I would have liked to go direct-drive, but didn't have enough space to inline the motor). The axis can reach 30m/min because servo max speed is 6000 rpm. Ballscrew critical speed is not a concern since it's short (400mm) and could in theory handle 13'000rpms.

Yes the axis is all steel, but the spindle is only 2.2kW ISO20 30krpm. The goal is high-speed aluminium milling.

Thanks for the link to the calculation software, this will be very useful to me.

Myself I think I am going to consider a 2005 ballscrew for the Z-axis. My ball screw length is also 400mm long and who would not appreciate a 15m/min rapid feed rate! Originally I planned for a 1605 with a 2:1 reduction, since I worried about whip (ball screw critical speed) and increased inertia (180W servos). These things are no longer an issue!

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[JAZZCNC]

Delta is Taiwanese and they make proper cheap servos. Also 400W Yaskawa servos can be found rather cheap (~$400 motor + drive + cables). Most similar sized servos have the same ratings. 6000 rpm is nothing special, same for absolute encoders.

I asked a quote for the latest ASD-A3 drives from Delta with a 750W servo, 24-bit incremental/absolute encoder. Price was $350.

But Jazz is right to warn you. Servos are more complex than steppers. I went Yaskawa just because their manual is more comprehensive than the Delta one.

I wasn't referring to Delta when I said Chinese servo's it was a general point between Cheap and Expensive Servo's. Regards the Yaskawa motors -drive-cable package then can you post a link to where your buying because that's a very good price. What model is that.?

Regards the speed I don't see many that are rated at 6k rpm in the lower price ranges, 3K rpm is a typical rating with incremental encoders. Yes, they can be run up to 5-6K rpm but they are not rated to run at that speed constant.!

[jarjar]

I wasn't referring to Delta when I said Chinese servo's it was a general point between Cheap and Expensive Servo's. Regards the Yaskawa motors -drive-cable package then can you post a link to where your buying because that's a very good price. What model is that.?

Regards the speed I don't see many that are rated at 6k rpm in the lower price ranges, 3K rpm is a typical rating with incremental encoders. Yes, they can be run up to 5-6K rpm but they are not rated to run at that speed constant.!

There are currently tons of offers on Ebay for SGM7J-04AF + SGD7S-2R8A00 at $450 new. I bought one like this a while back for a little less. I just asked for cables and they included them with no extra charges.
You can even buy the model with absolute encoder separately for less (SGM7J-04A7 $160 + SGD7S-2R8A00 $260)

I didn't say 6000rpm is the nominal rating, but it's still useful for short rapid moves.

[JAZZCNC]

JAZZ, what motors are you using to drive the ball screws and is the Z-axis motor with a brake? The Z-axis for my machine will be quite the same weight.

If you read one of my last posts in the build log http://www.mycncuk.com/threads/13448...823#post114823, I wrote that I will probably use Delta 400W servo motors and with a brake on the Z-axis. Well now I've got an offer for a full return from the supplier of those JMC 180W with integrated drivers, if I swap them for JMC 400W servo motors with integrated drivers. The problem here is that those JMC 400W servo motors does not come with a brake option.

The motors are 8Nm Lichuan closed loop steppers using 230Vac mains drives. It doesn't use a break because the gantry is vertical so Z-axis isn't fighting gravity, plus 8Nm is more than enough for this Z-axis even with heavy ATC spindle on it.

Regards the JMC then I've no experience using these motors or drives so I can't comment on how good or bad they are and I haven't looked at the specs, but if I'm honest I wouldn't use motors with integrated drives on a CNC machine. The heat and vibrations from the motors along with cutting debris, esp from aluminum coolant, etc, can't help with life expectancy but for me what's worse is the fact your running long signal wires back to the controller leaving you wide open to issues with interference from noise.

[NordicCnc]

The motors are 8Nm Lichuan closed loop steppers using 230Vac mains drives. It doesn't use a break because the gantry is vertical so Z-axis isn't fighting gravity, plus 8Nm is more than enough for this Z-axis even with heavy ATC spindle on it.

I totally missed that.. It is of course the X-axis in your case that could perhaps need a brake, but seems like its fine without.

Would there be any chance that a 400W Delta servo with brake couldn't handle my Z-axis of around 25-30kg, with a 2:1 reduction or even 1:1? I could go for 600W if that would be better.

Regards the JMC then I've no experience using these motors or drives so I can't comment on how good or bad they are and I haven't looked at the specs, but if I'm honest I wouldn't use motors with integrated drives on a CNC machine. The heat and vibrations from the motors along with cutting debris, esp from aluminum coolant, etc, can't help with life expectancy but for me what's worse is the fact your running long signal wires back to the controller leaving you wide open to issues with interference from noise.

Got it, thanks again. I will now completely forget about these servos with integrated drives.



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[jarjar]

Would there be any chance that a 400W Delta servo with brake couldn't handle my Z-axis of around 25-30kg, with a 2:1 reduction or even 1:1? I could go for 600W if that would be better.

I believe I already answered that in details...

[NordicCnc]

I believe I already answered that in details...

Gah you are right! In post #44 you did answer..

JAZZ, please ignore my repetitive question, and thanks jarjar for pointing out!

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[JAZZCNC]

There are currently tons of offers on Ebay for SGM7J-04AF + SGD7S-2R8A00 at $450 new. I bought one like this a while back for a little less. I just asked for cables and they included them with no extra charges.
You can even buy the model with absolute encoder separately for less (SGM7J-04A7 $160 + SGD7S-2R8A00 $260)

I didn't say 6000rpm is the nominal rating, but it's still useful for short rapid moves.

I'm surprised how much these have dropped in price, last time I looked, which must admit is quite some time ago, Yaskawa kits were like $900-$1100 range for 400W. I've never used them for this reason so I may look at these when a suitable job comes up.! . . . How easy or hard are they to setup/tune.? Do Yaskawa supply the Sigma tuning software for free.?

I'm surprised the absolute encoders are cheaper as well, not as many controllers about that can accept Absolute positioning so I would have expected them to be more. Thou absolute systems and Bus/Ethercat drives/controllers are coming down in price and more popular so maybe this is the reason.?

[JAZZCNC]

Nordic: Forgot to say in the previous post when mentioned about higher-level servos requiring higher quality components. That this is also true to lower degree for cheaper servos over a Stepper system.

For instance, with motor coupling used on Stepper, you can get away with more springy coupler and it won't affect the motor in any way. Whereas a springy coupler on even a cheap servo system can cause big issues with tuning the motor. The same goes if using belts and pulleys, buy good quality belts and pulleys.

The stiffer you can make the coupling between motor and screws the better this goes right down to motor mounting. Flimsy motor mounts etc will cause resonance which you'll have to tune out of the system. This isn't always so easy with cheap servo's so the more you can do to limit resonance the better.

[NordicCnc]

Nordic: Forgot to say in the previous post when mentioned about higher-level servos requiring higher quality components. That this is also true to lower degree for cheaper servos over a Stepper system.

For instance, with motor coupling used on Stepper, you can get away with more springy coupler and it won't affect the motor in any way. Whereas a springy coupler on even a cheap servo system can cause big issues with tuning the motor. The same goes if using belts and pulleys, buy good quality belts and pulleys.

The stiffer you can make the coupling between motor and screws the better this goes right down to motor mounting. Flimsy motor mounts etc will cause resonance which you'll have to tune out of the system. This isn't always so easy with cheap servo's so the more you can do to limit resonance the better.

I have never used servos before so I am not familiar with how the tuning works. All I know is that the Delta servos and most of the other servos comes with some auto tuning software. How good auto tuning works I have no idea.

Seems like tuning manually is very difficult and requires a lot of experience to get it right. If you don't know how to do it, the servo system would end up being even worse than a stepper system. I am starting to wonder if I would be better of with a good stepper system instead of diving into the realm of servos.

To me it seems like you favor steppers at for your own builds, but I may have got this wrong. If I am right, I guess you favor steppers for the simplicity and the above reasons?

By the way what would be a good supplier for belts and pulleys? What supplier are you using?

Thanks again for your great insight!


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