EMC2 - Pluto P (or Mesa 5120) - HBridge - DC Brush Servo

[DNB]

Hello Everyone,

I am pretty much a newbie on this forum, a newbie to motion control, an amatuer when it comes the CNC milling and I have had no experience or training when it comes to electronics. However, I am an obsessive tinkerer and have spent quite a bit of time studying motion control components and how they interact with one another.

I bought a milling machine a few years back (see picture below) to make parts for my various hobbies. The gentleman who sold it to me stated that it allowed 3-axis simultaneous control. This was not the case and for about a year now I have researched (on and off) for ways to upgrade the machine.

The other day, I was reading the forum and I came across SAMCO's post ([url]http://www.cnczone.com/forums/showthread.php?t=25929&highlight=pluto) where he discusses setting up a large a DC Servo setup on the cheap. I am also a cheap bastard so I was inspired by the thread. Not to mention grateful that free software as powerful as EMC2 exists!

If I understood the thread correctly, I can control my servo drives by using EMC2, a Pluto-P card (or Mesa Card) and a h-bridge. However, I need help with the following:

1. I do not know electronics so I doubt that I will be making my own h-bridge anytime soon. Does anyone know or can anyone recommend where I can buy an h-bridge that will work with my motors? The specs are as follows:

TORQUE CONT. AT STALL 2.7 Nm
AMP CONT. AT STALL 12A
VOLT 56V
RPM 2000 rpm
EXCIT PERM. MAGNET
INSULATION CLASS H
PLUSE CODER
AMB TEMP 40C
No D-172557
Date 81.8

2. My encoders are 2000 lines per rotation. Will this high resolution cause any problems under this setup? My screws are 5 TPI and I would like to get at least 300 IPM. I probably won't use 300 IPM but the machine can already go 300 IPM in rapid traverse (150 IPM for feed) so I'd like to keep that speed if possible.

3. My encoders are differential rather than single-ended. Does the Pluto or Mesa card allow for differential encoders or are they both single-ended? Does it matter?

4. I don't think I will need more than 4 axis of control and there a plenty of I/Os on the Pluto card. Since Puto is less expensive I will probably buy it when it becomes available. However, is there any reason why I might want to consider the more expensive Mesa 5120 instead?

5. What other components will I need for this setup to work? As mentioned before I do not know electronics. I would assume that I need to get myself a BOB and a power supply. Anything else? SAMCO was speaking of current limits and filters but I believe that was because he was building his own h-bridge. I hope their are available h-bridges that already take care of these items or there are readily purchased stand alone items that can hanlde this.

Thanks in advance for your help. I will post more pics as I progress.

David

[stustev]

This mill is a Yuasa/Enshu 3 axis CNC mill with a Fanuc System 3M control? If it is, it will certainly do 3 axis contour milling. Depending on the options in the control it could also do helical milling (milling a thread in a hole or on a boss) with the appropriate cutter.
I can see the advantage to putting EMC on it. The 3M control is very old. The parts will still be available but could (will) be very expensive. One board could cost more than putting EMC on it.
The Enshu mills are very rigid and very accurate. You have some very good hardware there. Some of the best anywhere. That is a jewel of a machine. You will not find anything any better, EVEN new will not be any better. Have I made my point? The mill is very much worth the upgrade to a new control.
Go to www.linuxcnc.org and join the users group. You will find invaluable help there.
thanks
Stuart

[DNB]

Thanks Stuart. I did look at linuxcnc.org but I did not realize they had a users group. I will check them out.

I think you are the first person to recognize the machine and know the controller. It is a great machine, works perfectly, and is very accurate. I definitely need to upgrade though because my 3M Model A controller does not do 3 axis contour milling. Plus it has SCR drives and I do not have true 3 phase service. I use a 3 phase converter and I was told that the drives do not work well or eventually do not work well without true 3 phase service.

I also looked into upgrading the controller through Fanuc but I got a price tag of nearly $5,000. I then looked at Mach 3 (with various different drives and interfaces) but I couldn't find the configuration I liked. I then stumbled upon Jon Elson's Universal PWM control and he introduced me to EMC2. His UPC is very affordable and I think I might go that route. However, using a pluto card with H-bridges sounds like it could be pretty fun plus it is also inexpensive so I would like to try it out.

I will also, eventually, upgrade the spindle motor so that the speed can be manipulated by the controller.

Thanks again,

David

[stustev]

You will find Jon very helpful and a joy to work with. I use his PPMC on a Dahlih 3 axis knee mill. I have had no problems with it since I finished the retrofit. The users-list is very helpful also. They will assist you in anything you want to try.

[extrapilot]

David

Having built a bunch of H-Bridge and stepper controllers, I strongly suggest that you consider just purchasing something like a Gecko G320. Yea, its $350 for 3 of them, but a decent HBridge which has optoisolation and is capable of 20A, with current limiting, is probably $50+ per, and then you still need the PWM/Quad interface for the PC (in the $60-200 range). So, for a savings of at most $100 (and possible 0), you are probably looking at headaches re: signal levels, sink vs. source current limits, EStop, etc. Like I said, I build motor controls, and I still opted to buy Geckos. They work great, and they are simple to implement.

Just sharing an alternative perspective.

Rob

[DNB]

Stuart:

Yes I have found Jon to be very helpful and it looks like he has excellent products. Currently, his UPC only allows for single-ended encoder signals and he has estimated that he will come out with a differential board early next year at the earliest. If I go with him I will need to deceide whether I want to wait until next year so that I can use my encoders' differential signals or if I will use the current UPC and go single-ended. I just wonder how important this is and if the increase in signal noise will be an issue.

___________________________________________

Rob:

Thanks for your comment. I looked very hard at G320's when I was considering using Mach 3. I am not sure how they would be integrated with EMC2. When I was investigating them, I called Gecko and spoke to Mariss who was also very helpful. Not knowing electronics I understood maybe 10% of what he said. However, if I recall correctly, he made it very clear that the 2000 count encoder would not work well with these drives and that the amperage of these encoders are almost certainly to high for these drives. He suggested that I replace the encoders with US Digital 500 CPR encoders which are fairly inexpensive. I just couldn't get myself to do it since I have perfectly fine 2000 count encoders which I believe gives me higher resolution. Perhaps, this isn't the case if with EMC2?

___________________________________

Still a pluto card for $60-$70 (or mesa for $200), plus H-Bridges for $50 a pop is very cheap. However, not knowing electronics, am I getting myself into something way over my head? Jon's UPC is $250, his Power Switch is $50 (not sure what this is for), and three PWM drives is $375. In total this comes to $675 which is very affordable.

David

[andy55]

Hello Everyone,
1. I do not know electronics so I doubt that I will be making my own h-bridge anytime soon. Does anyone know or can anyone recommend where I can buy an h-bridge that will work with my motors? The specs are as follows:

it would be nice if someone could publish an open-source design simple H-bridge servo amp. It can't be that hard to design but you do need some experience...
I'm using Jon Elson's PWM servodrives and they seem to work OK.

2. My encoders are 2000 lines per rotation. Will this high resolution cause any problems under this setup? My screws are 5 TPI and I would like to get at least 300 IPM. I probably won't use 300 IPM but the machine can already go 300 IPM in rapid traverse (150 IPM for feed) so I'd like to keep that speed if possible.

I'm using 4000 count/rev encoders with a m5i20 and there are no problems. If I remember correctly it can count up to 1 MHz pulses so that would be 15krpm with the 4000count encoders.

3. My encoders are differential rather than single-ended. Does the Pluto or Mesa card allow for differential encoders or are they both single-ended? Does it matter?

the differential encoders give you noise immunity, but you could try just using one signal of the pair.
If you do want the noise immunity you can convert the differential signal to a single-ended one with a simple chip. I did a small board for that:
http://www.anderswallin.net/2007/04/...der-interface/

4. I don't think I will need more than 4 axis of control and there a plenty of I/Os on the Pluto card. Since Puto is less expensive I will probably buy it when it becomes available. However, is there any reason why I might want to consider the more expensive Mesa 5120 instead?

does your machine have a parallel port so it can talk to the pluto?
I guess traditional pci-slots (m5i20) are going the way of the DoDo too, but most desktops still have them

5. What other components will I need for this setup to work? As mentioned before I do not know electronics. I would assume that I need to get myself a BOB and a power supply. Anything else? SAMCO was speaking of current limits and filters but I believe that was because he was building his own h-bridge. I hope their are available h-bridges that already take care of these items or there are readily purchased stand alone items that can hanlde this.

Power-supply for the servos (switch, fuse, transformer, rectifier, capacitors if you want to build it yourself). probably +5V and +12V supplies for the logic side and servodrives. Limit-switches, home-switches, emergency-stop switch. Coolant relay, something for spindle control, Jog-wheel?

AW

[extrapilot]

Hi David

Mariss is a great resource on drives.

I cant speak to EMC2. Im all for open source, but I went with Mach3 and am very happy I did; I dont want to spend lots of time with config files, and any weirdness with the kernel on a given PC/card/etc. Plus, there are lots of people running Mach with Geckos, and when something isnt running as expected- there are people who have already been there with your configuration.

On the encoders, you need to consider the realistic positional accuracy of your screws. If you have 5tpi screws, then a 4000 count/rev encoder resolves to .00005". Now, I can pretty much promise you that this is at least 10x tighter than your screws will provide (i.e most of us would be very happy with .0005" accuracy on a screw 1' or longer...). By simple math, a 400 count encoder will get you .0005" theoretical with your screws. The 500 count that Mariss suggested would be even better.

I suspect you can buy 3 Geckos, a project box, a parallel breakout card, and a nice surplus transformer/cap, along with a copy of Mach3, for $675.
At least, I was able to. I bought my transformers, rectifiers, and caps here: http://www.apexjr.com/

Regards,
Rob

[epineh]

it would be nice if someone could publish an open-source design simple H-bridge servo amp. It can't be that hard to design but you do need some experience...

There are a few people working on this idea, a good solid H-Bridge design would be great, two could be used for a stepper based design.

I am working on one myself, to go onto an EMC/Pluto-p based servo design, but I think it will be a little while yet.

Russell.

[DNB]

I found this H-bridge. Will it work with my motor specs (listed in the original post)? If so, I will need a snubber circuit too, correct?

http://www.tecel.com/d200/

Thanks,

David

[epineh]

I think the PWM frequency will be a problem with that drive, 1KHz is a little slow, normally a servo drive will be around the 20 KHz range.

The spec's mentioned sound very close to using IRFZ44 Mosfet's, which is what my H-Bridge will use, it wouldn't surprise me if that is what they are using for their drive.

It is cheap enough, just a shame about the frequency.

Russell.

[kestreltom]

David,

I know that you think you need an H bridge, but you have to understand that an H bridge is only one component of a decent servo amplifier (the electronic device which translates the logic signals from your computer into high power juice for your servos). Among other things, an EMC2 servo amp should provide current limiting, pwm signal input, enable, direction, etc. Using the feedback from the encoder, EMC2 takes over the control of velocity, position, and torque.

That is why Rob was suggesting that you look at the Gecko amps. The problem with Gecko amps, is that they are designed to accept only step and direction inputs. This is fine if you are using Mach3, but not if you are using EMC2. You can buy an additional device which will convert pwm from EMC2 into step and direction signals for the Gecko amps, but now you are looking at even more $$ to spend.

I don't have any connection to the following supplier, so I have nothing to gain from sharing this information.

Mesa Electronics makes the stuff you want and supports it for EMC2. I bought my 5I20 motion control board, and my 7I40L servo amplifiers from them. The price for the servo amp is $149.00 for a 2 channel board: ($75.00 per axis). The nice thing is that they make a high voltage version of this amplifier called the 7I40H which will suit your needs very well (same price). It is very small and efficient. It will also run at chopping frequencies that are high enough to be inaudible.

So long as your motors are equipped with 2000 ppr differential encoders, you are looking at getting your mill converted pretty quickly.
Forget about converting that toolchanger, unless you really like solving puzzles!

Good luck,
Tom