Building a controller for an LC 3024 -- what kinda servo amplifier?

[TimpanogosSlim]

So i came across an LC 3024 at PublicSurplus, bid on it, and won.

It does not appear to come with the controller, though the spindle inverter is still attached. Unknown condition according to the school district that put it up for auction, of course. There's no telling why. I actually haven't driven out to retrieve it yet.

I've read the documentation that I could find. Interfaced through a scsi card? Wild. Also not sorry I don't have that specific piece.

I have a brother-in-law who is a certified machinist but I don't want to wear him out with questions. I'm a beginner, in the sense that i have been messing around with 3d printers and the like for about 5 years.

I have a collection of OK quality wire crimpers in various styles, a pretty decent collection of soldering and desoldering equipment and I'm comfortable building cables, doing board level repairs, etc.

It's clear that, no matter what control solution i pick (leaning toward centroid acorn at the moment), I will need servo amplifiers.

I don't know anything about those.

What should i look for?

[joeavaerage]

Hi,
you need to positively identify the axis motors. If they are DC or brushless analog servos then you will need either servo amplifiers and a motion control capable of closing the loop (not
Centroid Acorn) OR servo drives that can close the loop like Geko G320's. Thereafter a Step/Dir controller like Centroid Acorn would work.

Many people buy second hand machinery and then try to re-use the existing servos...which are often old and from a previous generation of control. They reason that its cheaper to do so....
but come horribly un-stuck when they try to find old school drives and controllers which are anything but cheap and far from easy to do.

I would suggest that you look to replacing the entire servo and drive with new (and matched!) servos. I use Delta (Taiwanese brand, made in China) servos and others use DMM (Canadian brand,made in China).
Both are good quality, support, documentation and most importantly free set-up and tuning software at fair prices. For example:

https://www.fasttobuy.com/220v-127nm...ol_p28069.html

A 400W servo kit, including servo motor, drive and cables for $398 is good value.

Replacing your existing servos, if indeed they are older analogue types, will be so much simpler and also mean that you have a much wider choice of value for money Step/Dir motion controllers.

Craig

[TimpanogosSlim]

Hi,
you need to positively identify the axis motors. If they are DC or brushless analog servos then you will need either servo amplifiers and a motion control capable of closing the loop (not
Centroid Acorn) OR servo drives that can close the loop like Geko G320's. Thereafter a Step/Dir controller like Centroid Acorn would work.

Many people buy second hand machinery and then try to re-use the existing servos...which are often old and from a previous generation of control. They reason that its cheaper to do so....
but come horribly un-stuck when they try to find old school drives and controllers which are anything but cheap and far from easy to do.

I would suggest that you look to replacing the entire servo and drive with new (and matched!) servos. I use Delta (Taiwanese brand, made in China) servos and others use DMM (Canadian brand,made in China).
Both are good quality, support, documentation and most importantly free set-up and tuning software at fair prices. For example:

https://www.fasttobuy.com/220v-127nm...ol_p28069.html

A 400W servo kit, including servo motor, drive and cables for $398 is good value.

Replacing your existing servos, if indeed they are older analogue types, will be so much simpler and also mean that you have a much wider choice of value for money Step/Dir motion controllers.

Craig

Something is wrong with this forum because not only did i not get a notification that someone had replied, it still shows 0 replies in the forum.

Obviously before i buy stuff i will figure out what is or isn't working. it sounds like the original encoders may be a common failure point for example.

[ericscottf]

The motors are 48v DC brushed servos with 1k line ABZ incremental 5v encoders. The gecko 320s will work with them fine. You can even reuse the toroidal transformer in the control box to power the geckos and not have to get a new power supply.

Unless the original encoders were damaged, they are likely OK. not a likely failure point.
You could pull the motors off and get a full stepper kit if you wanted, but steppers aren't ideal.
Did you get the control box with it, and are only missing the PCI interface card for the computer? Or is the only major electronic part you have the inverter?

[TimpanogosSlim]

The motors are 48v DC brushed servos with 1k line ABZ incremental 5v encoders. The gecko 320s will work with them fine. You can even reuse the toroidal transformer in the control box to power the geckos and not have to get a new power supply.

Unless the original encoders were damaged, they are likely OK. not a likely failure point.
You could pull the motors off and get a full stepper kit if you wanted, but steppers aren't ideal.
Did you get the control box with it, and are only missing the PCI interface card for the computer? Or is the only major electronic part you have the inverter?

I haven't been able to retrieve it yet but the only major electronic part pictured with it is the inverter. I had planned to get it thursday or friday last week but nobody was answering the phone at the district warehouse. I will try to get in touch again tomorrow.

The Gecko 320 doesn't use the encoder signal, is my understanding?

It's a shame there isn't a 48v version if this board: https://makermotor.com/brushed-10-40...loop-feedback/

[Al_The_Man]

If they are analogue/torque mode amplifiers, look at Dynomotion/Kanalog as a solution.

[joeavaerage]

Hi,

The Gecko 320 doesn't use the encoder signal, is my understanding?

No, that is not correct, the G320 requires an encoder feedback signal. It is in fact just a more capable version of that drive you linked to.

Craig

[TimpanogosSlim]

Hi,



No, that is not correct, the G320 requires an encoder feedback signal. It is in fact just a more capable version of that drive you linked to.

Craig

I see. I was confused by their PID loop description.

I can't make any decisions until i have inspected the hardware. It's very hard to say with equipment that comes from a public education environment -- it could have been abused by students, it could have been barely used by faculty or staff, it could have been gifted to a school and never even set up. It's a crapshoot.

Happens in collegiate environments too. I had an uncle who was a physics researcher and avid ham radio operator, and he picked up two fairly rare 1kw AM transmitters from different universities where they were acquired somehow and then pushed into the corner of a lab and never ever used.

[Al_The_Man]

The nice thing about the Linux CNC, Kanalog, or even better still, Galil, is that there is no need for any feedback to the drive at all, simple transconductance/torque mode amplifiers can be used, the control loops are closed in the controller itself.

[ericscottf]

I see. I was confused by their PID loop description.

I can't make any decisions until i have inspected the hardware. It's very hard to say with equipment that comes from a public education environment -- it could have been abused by students, it could have been barely used by faculty or staff, it could have been gifted to a school and never even set up. It's a crapshoot.

Happens in collegiate environments too. I had an uncle who was a physics researcher and avid ham radio operator, and he picked up two fairly rare 1kw AM transmitters from different universities where they were acquired somehow and then pushed into the corner of a lab and never ever used.

Most often, with schools, we see they retired the computer and lost the control card that was in it. The main control box is usually there because there's no easy way to remove/lose it without undoing a lot of wiring.
If you want to operate the machine with the original controller, once you receive it, let me know. We do have the card in stock - you can have it up and running as a proper closed-loop servo system.

[TimpanogosSlim]

Most often, with schools, we see they retired the computer and lost the control card that was in it. The main control box is usually there because there's no easy way to remove/lose it without undoing a lot of wiring.
If you want to operate the machine with the original controller, once you receive it, let me know. We do have the card in stock - you can have it up and running as a proper closed-loop servo system.

Well, the original controller doesn't seem to be included in the lot. I can identify the inverter for the spindle, a box that may be the emergency stop but is up-side-down in the photo, and that's about it.

Until i get access to pick it up, the terrible pictures in the attached zipfile are what i know about it. I fear that maybe the warehouse staff took the same vacation days i did. I have doubts about my ability to load it without assistance, so if i have to wait until next week, things may get difficult. They specify that they do not load.

They said to pick up within 10 "business days" and I'm willing to argue that a day they weren't open wasn't a business day. They did not appear to be open last week.

It's possible that the control box and computer will show up in a future auction, or i already missed them in a past auction.

If i never get the original control box, and the servos are in good shape, the shopping list may look like:

Eltek Flatpack2 48v 2000w power supply and associated connection board for $100-120ish

3x Gecko G320X at $131/ea, or Leadshine DCS810 for maybe half that and a slow boat from china.

Some kind of motion control system - maybe acorn, maybe not, who knows. I have enough arduino and 3d printer bits that i could do some proof of concept halfass with grbl or whathaveyou. Admittedly i have no experience in CNC past using the omax waterjet system at my old makerspace that moved to TN on me.

And various wiring, cabinet, etc. Not including computer stuff i already have, maybe come in under a grand more to get it online? Including the publicsurplus fees and taxes i am only into this a little over $600 now.

[ericscottf]

Unfortunately, you're right, there's no control box there, I see the ends of the motor power cables.
I'd suggest you use a warp9 ess board with the gecko drives and a decent toroidal power supply from antec or similar. Not a switcher.

[TimpanogosSlim]

Unfortunately, you're right, there's no control box there, I see the ends of the motor power cables.
I'd suggest you use a warp9 ess board with the gecko drives and a decent toroidal power supply from antec or similar. Not a switcher.

Why a linear power supply, and how would you size it?

[joeavaerage]

Hi,
linear supplies, ie one with a transformer, and in the required sizes toroidal transformers seem to be the choice, are very rugged. They will tolerate 100%-200% overload
for brief periods whereas switch mode supplies will fault immediately.

I suppose that you could just add up the current of all three axis motors....but that tends to end up with a huge and costly supply. Its very seldom that all three axis motors
would ever be in a state of high demand simultaneously, most people go for something like one half to two thirds of the combined total.

I would before concerning myself with a power supply get the machine and then make a realistic appraisal of the existing axis motors. Many try to reuse them only to find they
spend untold dollars on compatible drives, power supplies and often a restricted choice of controllers that can be used. The other alternative is to use AC servos like Delta or DMM,
then you'l have no worries about matching motors and drives, and the models I'd recommend are direct off-line, ie 230VAC input, no power supply required.

Craig

[TimpanogosSlim]

Technically, the switcher goes into protection to prevent a fire or permanent damage to itself. But i see your point.

Multiple people recommending just throwing out the existing motors. If that happens i will probably buy the steppers that my brother-in-law upgraded past on his router.

[joeavaerage]

Hi,
overall linear supplies just seem to do the job better. No doubt the high quality switch mode supplies are as good as advertised, but the cheap Chinese stuff not so much.

Multiple people recommending just throwing out the existing motors. If that happens i will probably buy the steppers that my brother-in-law upgraded past on his router.

You need to get the machine and THEN make a decent appraisal. If the existing motors can economically and simply be reused then they'll beat steppers hands down.
If not simple or cheap to reuse them, then replacement is the only option.....steppers if you cant afford servos, but servos are by far and away the best recommendation.

Craig

[Al_The_Man]

Technically, the switcher goes into protection to prevent a fire or permanent damage to itself. But i see your point.

Multiple people recommending just throwing out the existing motors. If that happens i will probably buy the steppers that my brother-in-law upgraded past on his router.

Not sure who the "Multiple people" are ?
But I agree with keeping the existing if at all possible, I have never worked on said model of machine, but it appears some decent motors were fitted originally and definitely worth using IMO.
If you can do it, I agree, a servo closed loop system wins hands down over steppers.

[TimpanogosSlim]

Hi,
overall linear supplies just seem to do the job better. No doubt the high quality switch mode supplies are as good as advertised, but the cheap Chinese stuff not so much.

I actually find that the protection circuits on the cheap no-name supplies are almost non-functional -- overload them and they will just deliver choppy terrible power.

But the supply i specified is available online as surplus from telecom switching equipment. almost 40 amps of 48v for $90ish, plus a breakout board that plugs in where it used to slide into a backplane.

A 1000w antek supply would be marginally more expensive and a lot bigger/heavier.

Still not able to raise the school district warehouse - they may just be closed until next year.

[joeavaerage]

Hi,
most motors, excluding variable reluctance motors, ie steppers have two important constants:
1) Torque constant = so many Nm per Amp
2) Voltage constant = so many Volts per 1000 rpm

The later is also called the Back EMF constant. When the Back EMF of the motor is equal to the applied voltage the motor can go no faster.

The important point is that current is the determinant of the torque produced by the motor whereas the applied voltage determines the motors top speed.
Low voltage supplies implies low max rpm. 48V is pretty low by modern standards.

A direct off-line AC servo with 230VAC applied is after rectification and smoothing has a DC link voltage of 320VDC. This high(er) voltage ensures the motor can go plenty fast.

Until you can see and test the existing motors don't get hung up on a power supply....the motors, drivers and application determine the max applied voltage....not availability.

Craig

[TimpanogosSlim]

Hi,
most motors, excluding variable reluctance motors, ie steppers have two important constants:
1) Torque constant = so many Nm per Amp
2) Voltage constant = so many Volts per 1000 rpm

The later is also called the Back EMF constant. When the Back EMF of the motor is equal to the applied voltage the motor can go no faster.

The important point is that current is the determinant of the torque produced by the motor whereas the applied voltage determines the motors top speed.
Low voltage supplies implies low max rpm. 48V is pretty low by modern standards.

A direct off-line AC servo with 230VAC applied is after rectification and smoothing has a DC link voltage of 320VDC. This high(er) voltage ensures the motor can go plenty fast.

Respectfully, what kinda maximum speed is desirable in the kinematic axes?