CNC Mill Conversion Questions.

[Karl_T]

Re: more cnc Q.

The Galil DMC-2240 that have is a stand alone controller not a PCI Bus card so I have to go with RS232, Ethernet.

When you get into it, I'd like to know how Mach4 does things with Galil.

For example, when any input changes state, Galil sends a computer "interrupt" signal to the host computer. In the case of Camsoft, the host will then scan all inputs and run any code that's called out. The simplest examples is halt motion when a limit switch is hit or just turn on the coolant when another input is made. (this can also be done within Galil) Looks to me like Mach 3 doesn't have this at all.

Its also possible to write direct low level Galil programs and have the host just monitor position in Camsoft. Very useful for things like jogging with operator panel buttons, machine homing, rigid tapping, etc. looks to me like Mach 3 does not have this.

FWIW, I have a HUGE amount of experience working with the Galil motion products. Let me know if i can help.

 

[Rbeckett]

Just a quick heads up, There is a fellow on the Gecko controller group who has a surplus of more powerfull stepper motors for sale for a pretty decent price. Go to the Gecko group and read his post if you are interested. Here is the link: https://groups.yahoo.com/neo/groups/geckodrive/conversations/messages/22354 This will take you directly to the thread.

Bob

 

[Eddyde]

Regarding Mach3 and Galil

Mach4 may solve the problems I had with Mach3. What Mach3 did along with the Galil plugin is to try to operate the Galil card like a parallel breakout board, and that just overloaded the Galil buffer with hundreds of commands / second, rather than letting the Galil card actually control the motion. All of the motion control was being done in Mach3. The way it should work is to send a translated G-code line out to the Galil and let Galil figure out how to best execute the move, that is what is does for a living. IMHO whoever wrote the Galil plugin for Mach3 made a tactical error in the way they approached the task.

The above problems are what prompted me to write my own controller software, which I'll give away for free to anyone that can use it. It will only work with Galil products.

The best deal I could find on a 2908 module is $208.50, the 36 pin cable may be available from Galil, I can't find it anywhere else. If you use closed loop steppers, you won't need the 2908 module unless you want to use the AUX encoder inputs for another purpose.

Another option is to operate the steppers in velocity mode rather than step and direction. Then you would use the Main Encoder inputs for encoder feedback, and use the +/- 10 volt analog command signal to drive the steppers amps. In this mode, the steppers act just like servo motors. You do have to use stepper drives that will accept the analog input signal, normally +/- 5 volt or 0-5 volt input. It's no problem to program everything to do this. In a few days, I should have a couple of stepper velocity controllers that I bought for a project, I'm going to see if it's possible to run them from a Galil command signal.

The work you've done on your mill is very impressive and and a huge inspiration.
I hear what you are saying about the Mach 3- Galil interface, I am not married to using Mach 3, it just seemed like a good software at a very reasonable price. I am very interested in trying your software once I get to that stage. Otherwise, I found Mesh Cam and G-Wizard I wrote them about compatibility with Galil and am waiting to hear back. I did hear back from the Mach 4 folks and they said there is no Galil plug-in at this time.

I am leaning towards using brushed DC servos as they seem to be the best as far as accuracy, performance and are reasonably priced. Ideally, I would like brushless DC or AC servos as the seem to be the very best, but the prices I've seen so far are a bit (way) too steep. Basically I will start out with 3 axis on a Bridgeport size mill. I was hoping to spend about $1K for the motors, rotary encoders and amplifiers/drivers, package (not including the motion controller and its associated hardware). The stepper in velocity mode sounds interesting, I would like to explore that possibility further.

Then there is the issue of having linear encoders on the load, the Galil instructions say, to make them the primary encoders and the motor encoders the auxiliary, for their "improved dual loop" system (link to the Galil video).

So it looks like I will need the 2908, I've been watching eBay hoping to get a deal on it but if not, I'll get the one for $218. The cable is another issue. no one seems to have it. I might have to make one.

Many Thanks for you help.

Eddy

 

[Eddyde]

Re: more cnc Q.

When you get into it, I'd like to know how Mach4 does things with Galil.

For example, when any input changes state, Galil sends a computer "interrupt" signal to the host computer. In the case of Camsoft, the host will then scan all inputs and run any code that's called out. The simplest examples is halt motion when a limit switch is hit or just turn on the coolant when another input is made. (this can also be done within Galil) Looks to me like Mach 3 doesn't have this at all.

Its also possible to write direct low level Galil programs and have the host just monitor position in Camsoft. Very useful for things like jogging with operator panel buttons, machine homing, rigid tapping, etc. looks to me like Mach 3 does not have this.

FWIW, I have a HUGE amount of experience working with the Galil motion products. Let me know if i can help.

Thanks for the lead on Camsoft It looks like a great software but even the cheap-o version is way over my budget, at least for now. I also need a good CAD software, all the various hardware... Oh and a Mill too
I greatly appreciate any help you can give me.

Many Thanks

Eddy

 

[JimDawson]

Thank you for the kind words.

IMHO, there is no need for a dual loop system if the encoder is on the load. No encoders are required on the motors for positioning if there are encoders on the load. The really nice thing about only looking at the load for positioning is that there is zero backlash no matter what the lead screws are doing. (within limits)

Brushed DC servo motors normally have a tachometer on them that feeds back to the drive (amp) for speed control, this is not part of the servo loop. You can get away with lower torque (and thus less expensive) BLDC or AC servos than steppers because they won't decouple like a stepper. Most BLDC and AC servos are Hall comutated and this is fed back to the amp just like the tach output on the DC servo for the speed control. I'm using a combination of DC servos on the X and Y, and a stepper operating in velocity mode on the Z. The Galil card doesn't know it's running a stepper, it thinks it's a servo.

The load encoders could be rotary encoders on the leadscrews, or glass or magnetic scales on the table/quill. My preference is magnetic scales.

 

[Karl_T]

Just a note, the improved dual loop from galil is not available without <expensive> hardware upgrade to the galil card.

I'm installing a linear encoder on my mill in addition to the rotary. I'll play with destination control and dual loop control soon.

From what I've read, you won't be happy with Mach over galil until they upgrade.

I'd either toss the galil idea and get step servo drivers to go Mach.
Or even better, toss the galil idea and go linuxcnc with standard servo setup.
Or try out Jim's software.
Or take the DEEP plunge and go Camsoft.

my 2 cents

my

 

[Eddyde]

Thank you for the kind words.

IMHO, there is no need for a dual loop system if the encoder is on the load. No encoders are required on the motors for positioning if there are encoders on the load. The really nice thing about only looking at the load for positioning is that there is zero backlash no matter what the lead screws are doing. (within limits)

Brushed DC servo motors normally have a tachometer on them that feeds back to the drive (amp) for speed control, this is not part of the servo loop. You can get away with lower torque (and thus less expensive) BLDC or AC servos than steppers because they won't decouple like a stepper. Most BLDC and AC servos are Hall comutated and this is fed back to the amp just like the tach output on the DC servo for the speed control. I'm using a combination of DC servos on the X and Y, and a stepper operating in velocity mode on the Z. The Galil card doesn't know it's running a stepper, it thinks it's a servo.

The load encoders could be rotary encoders on the leadscrews, or glass or magnetic scales on the table/quill. My preference is magnetic scales.

Yes I want to put linear encoders on the load, in order to eliminate backlash error and achieve maximum accuracy.
The Galil site seems to say the best way to do this is through the "improved dual loop" but I take it you have had success with only the load feedback loop going to the controller and the motor feedback loop going only to the driver?

So you think I can get away with lower torque BLDC or AC servos? That would be great but may still be too expensive as the drivers are very pricy as well, I am struggling to figure out what that torque is. So far, I figured 750 watts for Brushed DC and around 1200 oz in for Steppers, this information is from others who have converted Bridgeport sized mills, what would the torque requirement be for BLDC or AC servos? I would appreciate any insight. Also is the torque requirement the same if a stepper is used in velocity mode vs step and direction?

Many Thanks,

Eddy

 

[JimDawson]

Yes I want to put linear encoders on the load, in order to eliminate backlash error and achieve maximum accuracy.
The Galil site seems to say the best way to do this is through the "improved dual loop" but I take it you have had success with only the load feedback loop going to the controller and the motor feedback loop going only to the driver?

So you think I can get away with lower torque BLDC or AC servos? That would be great but may still be too expensive as the drivers are very pricy as well, I am struggling to figure out what that torque is. So far, I figured 750 watts for Brushed DC and around 1200 oz in for Steppers, this information is from others who have converted Bridgeport sized mills, what would the torque requirement be for BLDC or AC servos? I would appreciate any insight. Also is the torque requirement the same if a stepper is used in velocity mode vs step and direction?

Many Thanks,

Eddy

My mill holds +/- 1 encoder count, theoretically equivalent to +/- 0.000039 in all axis. I guarantee it won't machine that close, just due to tool spring. Nor could I measure that close anyway. As best I can measure, I can hold 0.0005 over 12 inches.

750 Watts or maybe a bit less would be about right for brushed DC and BLDC motors, as is 1200 oz in for steppers. I think the brushed DC servos on my mill are about 500 oz in. I'm running the motors at 80 volts rather than the original 100 volts, and the maximum measured output to the motors 30 volts at 100 IPM. I did this because the stepper runs on a 80 volt power supply, and I wanted to just use one power supply. The Z axis is a 1200 oz in stepper and I cut the torque back on that to about 1/2 power. Normally you are running the motors at a fraction of their rated power, so theoretically you could get away with less power.

Yes the torque requirement is the same in both velocity and step mode.

 

[Eddyde]

My mill holds +/- 1 encoder count, theoretically equivalent to +/- 0.000039 in all axis. I guarantee it won't machine that close, just due to tool spring. Nor could I measure that close anyway. As best I can measure, I can hold 0.0005 over 12 inches.

750 Watts or maybe a bit less would be about right for brushed DC and BLDC motors, as is 1200 oz in for steppers. I think the brushed DC servos on my mill are about 500 oz in. I'm running the motors at 80 volts rather than the original 100 volts, and the maximum measured output to the motors 30 volts at 100 IPM. I did this because the stepper runs on a 80 volt power supply, and I wanted to just use one power supply. The Z axis is a 1200 oz in stepper and I cut the torque back on that to about 1/2 power. Normally you are running the motors at a fraction of their rated power, so theoretically you could get away with less power.

Yes the torque requirement is the same in both velocity and step mode.

I would love .0005" accuracy So I will try it you way, then if for some reason I cannot get it to behave I can always reconfigure it to the Galil dual loop system. The only hardware I would need to add is the 2908 and the illusive 36pin cable. I do like the philosophy of "less is more" so hopefully I won't have to go that route.

The motor info is very helpful. I'm still leaning towards Brushed DC as they are relitively cheap and their amplifiers are as well, unless there is an advantage to using steppers in velocity mode? On that note, Im curious to know why you chose the stepper Z axis? Also, if steppers are use in velocity mode do they still retain ther holding torque when not in motion? That might be an advantage?

Many Thanks

Eddy

 

[Eddyde]

Just a note, the improved dual loop from galil is not available without <expensive> hardware upgrade to the galil card.

I'm installing a linear encoder on my mill in addition to the rotary. I'll play with destination control and dual loop control soon.

From what I've read, you won't be happy with Mach over galil until they upgrade.

I'd either toss the galil idea and get step servo drivers to go Mach.
Or even better, toss the galil idea and go linuxcnc with standard servo setup.
Or try out Jim's software.
Or take the DEEP plunge and go Camsoft.

my 2 cents

my

The Mach 3 isn't etched in stone, so I will explore other software options. To start, I will likely take jim up on his generous offer and try his software. If it plays well with my system, happiness will abound!

The Galil DMC-2240 controller already has the dual loop capability built in. So if I go that route, I would only need to add the extra interconnect module and cable, about $300, not too bad. Ironically I only paid $275 for the motion controller NOS, about 1/10 its original cost.

Pleas keep me posted on how your dual loop set-up goes?

Many Thanks

Eddy