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Author Topic: Motion controllers - Take me to school  (Read 7248 times)

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Offline ger21

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Re: Motion controllers - Take me to school
« Reply #10 on: August 30, 2017, 05:30:54 PM »
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the advantages of AC servos with my thinking is speed, not cut speed, but speed regarding approach, plunge, and transfer all with improved resolution.

You probably already have all the resolution your Sherline can handle.
And you can get plenty of speed out of steppers, with the right steppers, drives and power supply voltage.

Get some Leadshine AM882's from Ebay, and some low inductance, high current steppers, and you'll get all the speed  and power you need. And they'll run smoother, cooler and quieter than what you have.


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I also want to say more torque is not what I am after.

You can't get more speed without more torque. Generally, acceleration requires more torque than cutting does.
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Another advantage is to use the external hardware drivers which I know steppers have as well but steppers are just noisy and don't like to be pushed very fast, at least open loop anyway. Using driver boards seems to be the way to go for more modern computer options.

You can't push a closed loop stepper any faster than an open loop stepper. When an open loop stepper runs out of torque, it stalls. When a closed loop stepper runs out of torque, the drive will fault. There's no magical power reserve to kick in when it loses position.

And I think you are confusing drives and motion controllers.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Motion controllers - Take me to school
« Reply #11 on: August 31, 2017, 04:21:40 AM »
Hi Mike,
you have some very good advice from some seriously experienced CNCers. It would appear that they all agree your machine could be maximised
by the right steppers/supply and drivers without the expense of either servos or hybrid closed loop steppers. My own modest experience with open loop
steppers is consistent with what they are saying also.

One thing you did comment on in an earlier post was that the old PCs you have been using for a parallel port controlled machine have been unreliable
and you wish to do better.

If you were to use an external motion controller then your choice of PC is much much broader and new and reliable PCs come into their own.
Because your existing control unit is integrated to use a separate controller will require that you use separate drives for your steppers, but you had
already come to that conclusion and were not phased about making the investment. If you were to buy three good quality drivers, say 80V and 7-8A
capable you could, in the first instance, continue to use your existing power supply and steppers. It maybe that just by improving the drivers that your existing
steppers now behave acceptably. If not you can upgrade the power supply and/or the individual steppers until you have achieved the level of performance
you are after. The advantage of this approach is that its progressive. You will have to stump up for an external controller, probably a breakout board or two
and three stepper drivers initially. Thereafter you can spread your purchases to suit.

I'm not familiar with the AM882 that ger21 recommended but guess they are similar to Gecko drivers, that is to say 80V 7A capable and quality/reliable build.
They can be had for about $150 each. There are a few choices of motion controller in the 'cost effective' end of the market, the ESS among them at $180.
Add a breakout board for $50 say...a total initial investment of $680.

Craig
My wife left with my best friend...
     and I miss him!

Offline ger21

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Re: Motion controllers - Take me to school
« Reply #12 on: August 31, 2017, 06:37:01 AM »
Actually, AM882's typically run about $75 each on Ebay, and I've got them for as low as $58 each.
The downside is they are unsupported, as they are I believe intended to be sold to the chinese market only. But yes, they are comparable to Gecko G201's, and some would argue that they are better.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Motion controllers - Take me to school
« Reply #13 on: August 31, 2017, 09:30:46 AM »
Hi ger21,
at $75 makes them very attractive, would save OP $225 on my scratch budget.

For whatever reason the Leadshine website times out when I try to browse.

Craig
My wife left with my best friend...
     and I miss him!
Re: Motion controllers - Take me to school
« Reply #14 on: August 31, 2017, 03:30:26 PM »
The AM882 is excellent. I have 5 running from an ESS, flawlessly. hey have an auto setup for getting a baseline, and a free software tuner for the finer stuff.
Re: Motion controllers - Take me to school
« Reply #15 on: August 31, 2017, 05:56:02 PM »
I have Leadshine as well, no problems at all.

Offline sn96

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Re: Motion controllers - Take me to school
« Reply #16 on: September 03, 2017, 02:05:26 PM »
I was looking at Clear Path servos and I'm impressed with the technology. They are very expensive servos but you get what you pay for. I don't think I would buy these for a Sherline mill, but I have discovered you can use these in-place of Sherline steppers. The SD series servos will accept step and direction signals with ease.
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP
Re: Motion controllers - Take me to school
« Reply #17 on: September 03, 2017, 09:05:38 PM »
Hi Mike,
very nice albeit expensive solution.

Most if not all modern servo drives accept step/dir inputs. If you really want a servo solution there are lots to chose from
ranging from expensive upwards!

Have you seriously questioned whether a stepper motor solution can achieve what you want?

Craig
My wife left with my best friend...
     and I miss him!

Offline ger21

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Re: Motion controllers - Take me to school
« Reply #18 on: September 04, 2017, 07:42:11 AM »
The biggest benefit the Clearpaths have, is that they are drop in replacements for steppers.
AC servos tend to be more powerful, and in many cases less expensive. But the frame sizes don't match steppers, so they are not quite as easy to implement on a stepper machine.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline sn96

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Re: Motion controllers - Take me to school
« Reply #19 on: September 04, 2017, 11:19:20 AM »
Hi Mike,
very nice albeit expensive solution.

Most if not all modern servo drives accept step/dir inputs. If you really want a servo solution there are lots to chose from
ranging from expensive upwards!


Have you seriously questioned whether a stepper motor solution can achieve what you want?

Craig

Yes I have thought about using different steppers but the speed and quietness of ac servos is very enticing to me. At my work I run an electronics probing machine that uses ac servos and it is never boring to watch it zip around stopping with in +/- 3 microns at each x/y location.

for under 2k you can have an awesome servo configuration. I paid 1k for a basic Sherline stepper system so as far as cost goes in comparison, its rather insignificant considering the performance gain.

I found drop in replacements for $270 each they are nema 23's with a 1/4" shaft the same as sherline steppers. A controller card would be needed And I found one for 159.90 os for  approx $970 you can have a 3 axis ac servo system that connects via any pc using an Ethernet port.

Here's the links:

Motion card:
http://www.ebay.com/itm/like/172287858504?chn=ps&dispItem=1

Servos:
https://www.teknic.com/model-info/CPM-SDSK-2311S-RQN/

Video:
https://youtu.be/-gigcf7ZzAQ
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP