NordicCNC's build log

[NordicCnc]

Its not easy or practical to put a bottom limit switch on the Z axis as the tool lengths will all vary .

True but my intention of using one is not to protect the tool itself, but to protect the machine from crashing into the BF12 floating bearing for any unintended reason. On my current machine I've been completely fine without any limit switches, but that machine is made with weaker stepper motors and is only running 4000mm/min at maximum feed rate.

[Clive S]

True but my intention of using one is not to protect the tool itself, but to protect the machine from crashing into the BF12 floating bearing for any unintended reason. On my current machine I've been completely fine without any limit switches, but that machine is made with weaker stepper motors and is only running 4000mm/min at maximum feed rate.

Have you considered soft limits?

[NordicCnc]

Have you considered soft limits?

No I have not, but that should work perfectly with position feedback from the servos. Thanks for the tip!

[NordicCnc]

Regards Motor brake then I can't answer that because I don't know those motors, but servos are not like steppers where they have a shaft sticking out the back, mostly because this is often used for the encoder.
Attachment 27530 Attachment 27531 Attachment 27532

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.

[jarjar]

A 400W servo (rated at 1.2Nm @ 3000rpm) is plenty enough. 200W is also probably enough.
I will be using a Yaskawa 400W servo with brake for a 60kg Z axis (moving part only), driven by a 5mm pitch ballscrew @ 1g accel and 20m/min.
The servo has a peak torque of 4Nm, and moving this axis will only require about 2Nm peak.

[NordicCnc]

A 400W servo (rated at 1.2Nm @ 3000rpm) is plenty enough. 200W is also probably enough.
I will be using a Yaskawa 400W servo with brake for a 60kg Z axis (moving part only), driven by a 5mm pitch ballscrew @ 1g accel and 20m/min.
The servo has a peak torque of 4Nm, and moving this axis will only require about 2Nm peak.

In post #2 http://www.mycncuk.com/threads/13448...672#post114672 you said that these 180W servos that I had bought were only toys and that 400W would be the bare minimum. I think you were talking about a little bit different design in that case so I can just ignore it, correct? Anyway the price difference between a Delta 200W servo and a Delta 400W servo is minimal.

Will you be using direct drive for that Z-axis? I checked that those servos are rated at 3000rpm, so direct drive with 5mm pitch would result in 15m/min. Also what diameter will that ball screw be and is it possible to spin it that fast?

Your moving weight sounds extremely heavy! Are you designing it in steel? How did you calculate how much Nm will be needed to move the axis?

Wow, this turned into a lot of questions, lol!

[jarjar]

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.

[JAZZCNC]

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.

Nordic be careful here because it's like comparing apples with oranges when comparing Yaskawa motors with Cheaper Chinese motors. The price difference is big and so is the quality. I'd also guess to get those speeds the Yaskawa will use an absolute encoder system with high count encoders requiring a high-frequency controller.

When you move up into these levels then everything else attached to them needs to move up in quality with it, else no point fitting expensive high-quality servos.
Your 8K budget will soon get eaten up with motors and ball-screws.

[jarjar]

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.

[NordicCnc]

Nordic be careful here because it's like comparing apples with oranges when comparing Yaskawa motors with Cheaper Chinese motors. The price difference is big and so is the quality. I'd also guess to get those speeds the Yaskawa will use an absolute encoder system with high count encoders requiring a high-frequency controller.

When you move up into these levels then everything else attached to them needs to move up in quality with it, else no point fitting expensive high-quality servos.
Your 8K budget will soon get eaten up with motors and ball-screws.

Thanks for the heads up JAZZ. I am set on using chinese servos anyway because of the price and their good reputation.

Regarding the controller pulse output then I don't think I need to worry. The ESS SmoothStepper can output up to 4MHz according to its specs.

Would you also have time to check my questions in post #44? I would really appreciate it man! http://www.mycncuk.com/showthread.php?p=114834

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