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What to buy for a new project
« on: June 10, 2020, 08:39:54 PM »
Hi,
price scales exponentially with size, particularly if you require the rigidity to machine aluminum. If you want to machine
steel then factor at least a five-fold increase in rigidity, in fact a router table is the wrong design for ferrous materials, for those
you need a mill.

PMDX controllers are parallel port for Mach3. The only PMDX external motion controllers are for Mach4.

Do you wish to persue a parallel port or do you wish an external controller?

Leadshine have a range of controllers that are very capable but less costly than Geckos, the AM882 for example.

34 Size steppers have great torque but are as slow as a wet week....if you must use 34 (or bigger) then select models with
the lowest possible inductance or you will be dissapointed.

If you are of the opinion that you need the torque that you can get from 34 size steppers you should consider AC servos, an
appropriately sized servo will leave any stepper in the shade.

Craig
My wife left with my best friend...
     and I miss him!
Re: What to buy for a new project
« Reply #1 on: June 10, 2020, 09:59:01 PM »
Thank you, Joe,
Great points to start with.

No plans to get into steel, thankfully.  Wood and plastic are the baseline for this router.  Aluminum sheet is my "reach" goal.  If I get there, I should not hope to hold tight tolerances.

The PMDX controller I suggested is based on the assumption that I can run Mach4 on the laptop and it will direct the controller via USB, which then directs the motor drivers.  Any flaw in that simple picture?  I haven't figured out what the value in having a parallel port connection would be if I am setting up a new machine and control system from scratch.

The size 34 stepper was the starting point since I see so many of these, and the McMaster Carr website has a very detailed spec sheet.
Now that you mention it, an AC servo definitely will have the guts to move anything, but doesn't that complicate the motor driver and controller?

Perhaps you can tell already, that I only know enough to be dangerous.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
Re: What to buy for a new project
« Reply #2 on: June 10, 2020, 11:11:24 PM »
Hi,

Quote
The PMDX controller I suggested is based on the assumption that I can run Mach4 on the laptop and it will direct the controller via USB, which then directs the motor drivers.  Any flaw in that simple picture?  I haven't figured out what the value in having a parallel port connection would be if I am setting up a new machine and control system from scratch.

USB is a poor choice for controller interconnection, it works but is noise prone, better Ethernet. If memory serves the only all the PMDX controllers are USB connected,
which would be their only weakness. An Ethernet SmoothStepper is a viable alternative. But, otherwise yes, the PC connects to the motion controller either USB or
Ethernet, and the controller connects, via in some cases a breakout board, to the motor drivers, limits/homes/probes and Estop as required.

Quote
Now that you mention it, an AC servo definitely will have the guts to move anything, but doesn't that complicate the motor driver and controller?

No. The AC servo is iteslf a fairly detailed and complex setup task but the connection to the motion controller is as straight forward as a stepper.

Craig
My wife left with my best friend...
     and I miss him!
Re: What to buy for a new project
« Reply #3 on: June 11, 2020, 12:01:26 AM »
Ethernet suits me...  visions of sitting on the couch and checking job progress...  better not get too far ahead of myself.

Thanks for the confirmation of the system basics.  And over-simplifying it for me now.  I've got a fair background with arduinos and such, but for this project it seems like I'd better go back down to the bottom of the learning curve. 

Looks like the AC servos and drives are more expensive than steppers, but perhaps just because they go up in size quickly, while steppers with more than 1 N*M torque seem rare.

Can you offer any insight into typical torque curves for servos? 

The McMaster-Carr steppers include torque curves that lose torque linearly down to some small torque value at the rated speed.  It would be most helpful for the case of servo motors if their torque curve doesn't just drop off immediately.  A constant torque range would help a lot in choosing servos over steppers on the gantry motion.  A chart like this one below would tell me that a servo has a constant torque region, but I'm on a budget, so I probably won't be buying from  Kollmorgen or Rockwell.  Do all servos have this property, even cheap ones? $$$   :-[

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
Re: What to buy for a new project
« Reply #4 on: June 11, 2020, 02:47:04 AM »
Hi,

Quote
Looks like the AC servos and drives are more expensive than steppers, but perhaps just because they go up in size quickly, while steppers with more than 1 N*M torque seem rare.

Yes, good quality servos but still not 'top shelf' are close to double the price of a stepper and drive.

All steppers lose torque the faster they go. The higher the winding inductance the worse the torque degradation. Most run of the mill
cheap 23/24 size steppers with 6mH inductance have as little as 5% of their holding torque at 1000 rpm. If you choose wisely and get steppers
of 1-1.5mH they may retain 35%-50% of their holding torque at 1000 rpm.

34 Size steppers have a lot more torque, 1200 oz.in is common but have very much higher inductance also and therefore will probably
not be much good beyond 500rpm.

All steppers, irrespective of size have no overload capacity, the first time you know that you are approaching the torque limit (at the given operating
speed) is a missed step or stall. Servos on the other hand just 'dig in', and produce the extra torque, commonly three to four times rated torque
with a heat limited duration.

The torque/speed diagram you posted is normal for servos. My Delta servos have torque/speed curves exactly like that.

I suggest you look at Delta, a Taiwanese brand manufactured in China or DMM, a Canadian brand manufactured in China, both good quality
and well supported that won't break the bank. There are even cheaper no-name Chinese brands but of questionable quality, support and
documentation, none-the-less seem good value.

Well chosen (low inductance) steppers with the best highest voltage drivers and highest voltage power supply deliver great results when used within
their envelope, but the operative words here are 'within their envelope'. If you attempt to stray out of that envelope they stall, no ifs or buts, they stall.
Having said that they have a great deal of torque in a small package, better than servos pound for pound. Where servos show their strength is
their overload capacity and speed, but you buy those advantages at a hefty price.

Craig
My wife left with my best friend...
     and I miss him!
Re: What to buy for a new project
« Reply #5 on: June 11, 2020, 10:25:30 PM »
Thank you Craig,
(I guess you did something called a "thread split")

You have confirmed a number of things I've seen in the stepper datasheets, which were going to pose a problem, but now I can avoid them.

Pointing me at DMM may also prove valuable - the 3-axis starter kit looks like what I'm looking for.
Interfacing the included breakout board seems to be a direct ethernet cable connection, like what you suggested.

That kit also includes a power supply.  In many DIY CNC projects, I see a big toroid.  Will one be needed for a servo kit like this?
I will also look at Delta and explore the offerings on e-bay.
Thank you again for the good leads!
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
Re: What to buy for a new project
« Reply #6 on: June 12, 2020, 01:08:25 AM »
Hi,

Quote
(I guess you did something called a "thread split")

No. I didn't but probably Tweakie, he is an active forum moderator.

Quote
That kit also includes a power supply.  In many DIY CNC projects, I see a big toroid.  Will one be needed for a servo kit like this?

DMM have two types of servo drives, the DYN2 which requires 75VDC input, so a high current power supply will be required.
The DYN4 however, a few dollars more, has 230VAC input, so no power supply required. The higher voltage allows full exploitation
of the servo whereas the low voltage driver cannot quite extract all that the servo is capable of.

Delta B2 series (160,000 count encoder), A2 series (1,280,000 count encoder and load sensing), A3 series (24 bit absolute encoder) and B3 series
(24 bit absolute multiturn encoder) are all 230VAC input, so no extra supply required.

Craig

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

Offline Tweakie.CNC

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Re: What to buy for a new project
« Reply #7 on: June 12, 2020, 02:54:03 AM »
Quote
No. I didn't but probably Tweakie, he is an active forum moderator.

No, it was not me guys.

Tweakie.
KEEP SAFE !
Re: What to buy for a new project
« Reply #8 on: June 13, 2020, 12:14:09 AM »
Tweakie,
I'm a moderator on another forum, so one of the interesting things about Machsupport.com is how it's set up to use Simple Machines in such a different way from the other one.  The look is totally different, and yet, there at the bottom of the page is "SMF 2.0.15".  I hope it's working well for you - we had to hire a part-time tech support to deal with "security" issues.

Back to the other not-so-simple machines...

Thanks again for the additional suggestions.  I'm looking at Delta and really impressed, technically.  This is the part where I check carefully "how fast do I want to spend?"  I probably don't need the Deltas, and if my gantry router starts to make them necessary, then it actually means I'm being too ambitious.

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Re: What to buy for a new project
« Reply #9 on: June 13, 2020, 02:04:58 AM »
Hi SparWeb,

Don't know why but I still use the old layout although there are a few different 'looks' to choose from.
The SMF has it's moments but overall it is good, there are a couple of things I would like to change but the boss doesn't let me anywhere near any of the settings.  ;D ;D

Tweakie.
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