Choosing the right Steppers/Servos and the right Control Software

[twilliamson]

I have embarked on my fully custom CNC project. I some experience with cnc routers, i built and used a original shapeoko, and work with a shop sabre cnc plasma from time to time. I am building a 30in by 50 inch machine, based on the probotix design dual x driven. Wood, maybe some light brass/aluminum. I have 1505 china special ball screws and am almost to the point were i need motors.

Clearpath's are not out of the budget, but not hell bent on using them either.

I dont really want to throw money at something i dont need but im trying to decide between LinuxCNC and Mach 3. Im also leaning to parallel port interface, vs ethernet smooth stepper. I dont think i will need that many extra i/o ports, but if the parallel port isnt going to be fast enough...

My questions..
Clearpath or not? CPM-SDSK-2321S-RLN
Clearpath PSU or Generic?

LinuxCNC or Mach 3?

Parallel Port or Ethernet Smooth Stepper?

Why/Why Not. Using the Linux CNC and Parallel port helps me justify Clearpath servos.

Im sure this is covered elsewhere but didnt see any really good answers.

TW

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[ger21]

If your comfortable with Linux, then there's no reason to use Mach3, as LinuxCNC is better at this point in time.

As for motor choice, it's a little more difficult. To answer the question properly, depends on how fast you want to move, and accerelate, and how much weight you're moving.

Personally, I think you can get performance close to or equal to Clearpaths for a lot less money.
Leadshine AM882 drives from Ebay, and motors like these running on 50V-60V.
High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Stepper Motor | Stepper Motor Driver | CNC Router | Laser Machine | 3D Prin

[wizard]

These day i really think trying to run your G-Code processor over a parallel pirt is foolish. Plan on buying extra hardware to handle the real time I/O. This applies to both LinuxCNC and Mach. This doesn't mean you can't run LinuxCNC over a parallel port just that it is an amazing hassle to find hardware that works properly. Finding that hardware becomes more difficult every year. To be honest you seem to be obsessed with cutting corners here when the additional hardware is a minor part of the overall budget. Also Mach 3 has been replaced by Mach 4.

As for Servos vs steppers that is really up to you and your performance expectations. Each solution has its benefits. On a light duty machine id go with steppers myself. Steppers with modern drivers are good performing motion solutions.

Beyond all of this i really don't grasp the logic you are using to say LinuxCNC and a parallel port justifies Clearpath Servos. How does a low end troublesome port justify a high end (mid range maybe) motion system? I don't get it. The greater the expense of the motors/drives the more likely id want the confidence of a system that can reliable drive them.

[ger21]

These day i really think trying to run your G-Code processor over a parallel port is foolish.................How does a low end troublesome port

It's only troublesome if it doesn't work. The fact is, tens of thousands of people are running machines from the parallel port, with no troubles at all. Myself included.

I wouldn't use the parallel port on a new build today, though, as the cost to use dedicated hardware is so low. Under $100 for a Mesa card for LinuxCNC.
But the parallel port is still a viable option for many.

[twilliamson]

So my logic is ... if i have GREAT motors, but crappy parallel performance.. grab a Ethernet smoothy board.. problem solved...no hardware is being replaced... well nothing expensive. Might could save a buck...

I guess the work i did with the grbl shield on my shapoko has me gun shy on steppers.. That thing has a crappy driverboard.

Whats this mesa board? I know there are tons of hardware interfaces.

What exactly should i be measuring as far as mass? Gantry+Router?

[NIC 77]

So my logic is ... if i have GREAT motors, but crappy parallel performance.. grab a Ethernet smoothy board.. problem solved...no hardware is being replaced... well nothing expensive. Might could save a buck...

I guess the work i did with the grbl shield on my shapoko has me gun shy on steppers.. That thing has a crappy driverboard.

Whats this mesa board? I know there are tons of hardware interfaces.

What exactly should i be measuring as far as mass? Gantry+Router?

Read through some of my posts pertaining to motors and ball screws.

What are your expectations for speed and acceleration?

You've already bought 1605 ball screws? I can tell you right now that you could have a problem with critical speed if one of your axis has a 50 inch travel and you want to go fast. How do you feel about 200 - 250 IPM max? If you're OK with it, that's no problem. It depends on your expectations. Or is the 50" not the travel but an overall dimension? Do some searches on ballscrew critical speed.

You need to match your motors (speed vs torque graph) to the lead of ballscrew you are using, the weights that the ballscrew must move (this includes everything the screw must accelerate and decelerate), the acceleration that you want, and the top speed you want to achieve.

Also, you must consider the critical speed of the screw.

You could buy the most expensive clearpath servos you can find and still end up with a turd if you don't match the entire system correctly for the desired performance parameters you want to achieve.

[wizard]

It's only troublesome if it doesn't work. The fact is, tens of thousands of people are running machines from the parallel port, with no troubles at all. Myself included.

Exactly! If it doesn't work it is very troublesome and finding the trouble free boards and BIOS's gets harder everyday. If somebody building a machine has a supply of old mother boards known to be good then the parallel port really isn't a problem for a low end machine. The problem is if the board is newer (no parallel port anyways) or has one of the dreaded BIOS and systems management unit known to screw up real time operation it isn't too good.

I wouldn't use the parallel port on a new build today, though, as the cost to use dedicated hardware is so low. Under $100 for a Mesa card for LinuxCNC.
But the parallel port is still a viable option for many.

Viable maybe, but I can hardly advise people to go this route if they have to buy new hardware. As you note the right hardware is fairly cheap.

[twilliamson]

Read through some of my posts pertaining to motors and ball screws.

What are your expectations for speed and acceleration?

You've already bought 1605 ball screws? I can tell you right now that you could have a problem with critical speed if one of your axis has a 50 inch travel and you want to go fast. How do you feel about 200 - 250 IPM max? If you're OK with it, that's no problem. It depends on your expectations. Or is the 50" not the travel but an overall dimension? Do some searches on ballscrew critical speed.

You need to match your motors (speed vs torque graph) to the lead of ballscrew you are using, the weights that the ballscrew must move (this includes everything the screw must accelerate and decelerate), the acceleration that you want, and the top speed you want to achieve.

Also, you must consider the critical speed of the screw.

You could buy the most expensive clearpath servos you can find and still end up with a turd if you don't match the entire system correctly for the desired performance parameters you want to achieve.

So may Critical Speed is about 1200 RPM on the X axis and 3300 on the Y. I assume that you run into issues where the rod would "whip" causing you issues, if you run it any faster..
(per Nook Ind.)

That works out to 235 IPM... Is that a OK speed?

[twilliamson]

Im not sure on my gantry weight just yet.. but looks like 250 to move it unloaded. between two motors, thats nothing.

What is a good rule of thumb for "fources required to cut"? IE would i need 50,75,100lbs of force to cut, wood, alum, brass?

Novice here...

[ger21]

That works out to 235 IPM... Is that a OK speed?

You'll probably wish it was much faster. But I wouldn't count on getting more than 800-1000rpm. if you're using steppers. 1200 might be possible, but that's optimistic.
You really should have bought 1610 screws.

What is a good rule of thumb for "fources required to cut"? IE would i need 50,75,100lbs of force to cut, wood, alum, brass?

You probably won't see much more than 25-35lbs of cutting force. The force required for acceleration is much higher.

[twilliamson]

Leaning towards this fleabay kit.


3pcs Nema 34 stepper motor 85BYGH450C-012B dual shaft 3.5A 11.5N.m(1600oz-in) 151mm

3pcs stepper motor driverQ860MA 7.8A 80V 256Microstep

3pcs power supply:350W 60V

[ericclinedinst]

Eh. If you're looking for speed you definitely don't want 1600 oz in motors on such a small machine.

I really think before you buy anything else you need to do more research. Like Gerry said, you should have gotten 1610 screws. Buying that setup is going to be another wrong choice.

Leaning towards this fleabay kit.


3pcs Nema 34 stepper motor 85BYGH450C-012B dual shaft 3.5A 11.5N.m(1600oz-in) 151mm

3pcs stepper motor driverQ860MA 7.8A 80V 256Microstep

3pcs power supply:350W 60V

[twilliamson]

Eh. If you're looking for speed you definitely don't want 1600 oz in motors on such a small machine.

I really think before you buy anything else you need to do more research. Like Gerry said, you should have gotten 1610 screws. Buying that setup is going to be another wrong choice.

1:2 Gearing?

[ger21]

Leaning towards this fleabay kit.


3pcs Nema 34 stepper motor 85BYGH450C-012B dual shaft 3.5A 11.5N.m(1600oz-in) 151mm

3pcs stepper motor driverQ860MA 7.8A 80V 256Microstep

3pcs power supply:350W 60V

What I recommended earlier will be at least 5x faster.
For speed, you want motors with the highest current, and lowest inductance you can find.

[twilliamson]

What I recommended earlier will be at least 5x faster.
For speed, you want motors with the highest current, and lowest inductance you can find.

Im on board. What about the drives? Are they that much better?

[ger21]

The AM882 drives are cheaper than the DQ860MA and should be as good or better. They also can be configured with software for more control.

[pirate323i]

The AM882 drives are cheaper than the DQ860MA and should be as good or better. They also can be configured with software for more control.

Dont mean to hijack... but is the current recommendation for this style of drive over gecko g540?


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[louieatienza]

The AM882 drives are cheaper than the DQ860MA and should be as good or better. They also can be configured with software for more control.

Not sure if the AM series drives had been discontinued and supplanted by the EM series? They are nice and have sensorless stall detection as well. I think however if one can get by without that (as we've done for a long while now), and software control, the DM series is just as good for a little less.

[louieatienza]

With two 380oz-in steppers and 48V, you should be able to achieve at least 1200rpm with enough torque to get that gantry moving. Easily.

Exactly! If it doesn't work it is very troublesome and finding the trouble free boards and BIOS's gets harder everyday. If somebody building a machine has a supply of old mother boards known to be good then the parallel port really isn't a problem for a low end machine. The problem is if the board is newer (no parallel port anyways) or has one of the dreaded BIOS and systems management unit known to screw up real time operation it isn't too good.

A PCI parallel port card can be had for under $20. CPU throttling and power management can be turned off in the BIOS relatively easily. And it's not like USB or Ethernet options guarantee smooth sailing, as anyone would find out by perusing the forums for those products. Besides, most every stand-alone motion controller card has a 26-pin ribbon cable header or DB25 connector, with configurable pin in/pin out if necessary, so upgrading to one after the machine is up and running is no big issue. It can be done down the road.

That works out to 235 IPM... Is that a OK speed?

I think that's fine. 12 seconds to transverse the entire gantry travel is not too bad. Frankly, other than homing your machine, rare is the occasion that you transverse the entire machine travel so many times during a job that it actually affects machining times. Unless you program a job that way.

There is nothing for "free" in engineering. No matter what part you're designing, what you gain in one aspect is lost in another. Using all the best components money can buy is not engineering - any yo-yo can do that. It's having a system that's balanced for the intended purpose that matters. Since you already have the screws, you really don't need steppers with huge stall torque ratings. Like I mentioned, 380oz-in or even 300oz-in, with 48V PSU, will do the job just fine. You're cutting wood - not facing a hunk of steel with a shell mill.

[ger21]

Not sure if the AM series drives had been discontinued and supplanted by the EM series?

From what I understand, yes. They must be still making and selling them in China, though, as they are readily available on Ebay. What makes them attractive is that they are close to half the cost of the EM drives. The last ones I purchased were $58 each. The downside is that you get no support.

Dont mean to hijack... but is the current recommendation for this style of drive over gecko g540?

Depends on how much power you need, and if you want individual drives, or an all in one package. The G540 is limited to 3.5A and 50V. I'm running my motors at 5 amps and 60V

Imo, the AM882 is comparable to a G201X, but at half the price.