Need Hardware Choice Help

Hello all. I'm just starting out on my first CNC project and thinking EMC2 might be the ticket for my control software. First the machine.

BF20 Mill converted to CNC with 5 TPI ballscrews, 3 Axis with a 4th and possibly 5th axis in the future, Spindle Control for use with ridgid tapping., ATC with pneumatic drawbar

Now I was going to go with stepper motors but not to sure if I shouldn't just use servo's. I was going to go direct drive stepper with 2x 570oz motors and 1 906oz motor driven by Keling digital KL-5056D drivers and a C35 break out board.

Well I want to kept the electronics under $1K if possible. I already have a PC that showed something like 12K for servo latency and 10K for max latency I think it was. They where all under 15,000 which I've read is stealer. I want precision and maybe servo control would be the best bet when using EMC2. I'm very electrically inclined so I can handle just about any install with ease just I don't know what to use.

I want to take full advantage of closed loop operation or should I say full advantage of EMC2. I don't want missed steeps as some of the things I'm looking to mill need precision and .001" could possibly ruin the piece.

So would stepper motors be ok for this or do I have to go Servo drive for what I'm asking?

If Servo drive can I go direct connection or do I have to use like a 2:1 belt drive setup?

The Mesa hardware looks amazing but their are so many options and FPGA cards I have no clue which one to go with. The 5I23 and 7I43 looks to be a good solution. I'm also wanting to use a pendant for manual control when needed and the 72 I/O pins seems like the ticket, but I could always just use a PP interface for a pendent as well, or a USB one. I don't know what daughter cards if any to get to actually hook into the I/O pins of the 5I23 or even the 7I43 if it is maybe a better option.

What servo motors and controllers should I be looking at? I'm sorry to ask so much in my first post. I have played around with EMC2 a little and so far I really love it. Since I haven't purchased my electronics yet I'm asking these questions instead of how do I get my current electronics to work.

Thank you for any and all advise given.

I'm in the planning stage of my build. The mill is on back order until the end of the month. Wow I really am not sure what components I would need to purchase for a servo config. Maybe I should just kept it stepper and get the 7I43.

I just don't know what I need to get to go servo. Like which Servo motors, Drivers, Encoders. And the cost looks like I might not be able to do 3 axis for around $1,000. But I don't know. Does this sound logical?


350oz-in Peak NEMA 23 60VDC DC Motors x3
Geckodrive 320x x3
50v/20A Unregulated Power Supply
US Digital 300 CPR Encoders x3
Mesa 5i20
Mesa 7i33TA
Mesa 7i37TA


This is a step/dir setup so It's still no closed loop correct? What would be a good place to get a servo amplifier to be able to run closed loop as it looks like that is all I would really need instead of getting a step/dir servo driver. Or maybe I'm not completely understanding how a servo system is setup.

This is still step/dir. If you use mesa cards you dont need the 7I33TA (thats for analog servo interface), so either a 7I42TA or 7I47TA would make more sense as a breakout for the step+dir signals and possible encoder feedback. (7I42 if you have TTL output encoders, 7I47 if you have differential output encoders)

Ok I think for this build I'll just go with steeper motors and the PP Card C35 that I was already planning on going with. I can still use EMC2 just not have all the cool features that I was looking at. For my next build I should have the info for what is needed for closed loop servo control and have a machine that would warrent using servo's.

TY for the help. I still think I might pick up a 5i20 down the road and start learning how to set it up.

Ok I think I found my hardware. It's the DMM A/C Servo High Torque 3 axis kit . The kit offers limit switches, E-stop, Servos, Servo drives, encoders, cables, and PP BOB. According to the info on the servo drive it can also worth with an analog input of 0-5v and a direction input. Would that fit the bill for closed loop operation? I'm thinking to get it running and learn the ins and outs that I'll run it step/dir and later go to a 5i20 set-up. This Looks like it would be a very well priced kit and pretty much fits my current budget almost perfectly. I'm not to sure what the output on the encoders are but it's something like 16384 CPR and 4096 CPR accuracy. They say it's a 14bit running 12bit.

As long as the drive will function in analog mode w/o the encoder hooked up to it I think it will work. I'm also going to hook these up direct drive. With their high constant torque and low speed coupled with the high encoder CPR it's just the logical way to go about it. I'll have to counter ballance the Z-Head but I'm going to try w/o a counter balance first. What do you think of this set-up?

Maglin wrote:

Ok I think I found my hardware. It's the DMM A/C Servo High Torque 3 axis kit . The kit offers limit switches, E-stop, Servos, Servo drives, encoders, cables, and PP BOB. According to the info on the servo drive it can also worth with an analog input of 0-5v and a direction input. Would that fit the bill for closed loop operation? I'm thinking to get it running and learn the ins and outs that I'll run it step/dir and later go to a 5i20 set-up. This Looks like it would be a very well priced kit and pretty much fits my current budget almost perfectly. I'm not to sure what the output on the encoders are but it's something like 16384 CPR and 4096 CPR accuracy. They say it's a 14bit running 12bit.

As long as the drive will function in analog mode w/o the encoder hooked up to it I think it will work. I'm also going to hook these up direct drive. With their high constant torque and low speed coupled with the high encoder CPR it's just the logical way to go about it. I'll have to counter ballance the Z-Head but I'm going to try w/o a counter balance first. What do you think of this set-up?

Does CPR mean cycles/rev or quadrature counts/rev? If it is cycles/rev, then you get 16384 x 4 = counts/rev.
With software generating step pulses, you won't even be able to get 60 RPM out of these motors. You'd need 65536 step pulses/second to do one rev per second = 60 RPM. You would almost certainly need a hardware
step generator to provide enough step pulses to get reasonable speed. Even if it is counts/rev, then you'd still
only be able to get about 50,000 step/second divided by 16384 = 3 revs/sec = 180 RPM. 180 RPM direcly driving a 5 TPI leadscrew gives 36 IPM.

Jon

TY for steering me straight. Ok this is a for sure motor and servo drive setup. I just bought the servo drives. They are AMT BD30A8B drive's and I'm going to use 3x 850oz. 90v/30A peak 3000RPM servo's and AMT102-V TTL Differential encoders. The servo drives are PWM/Dir drives. I think they might do closed loop but if not they at least are good drives or so I think.

So for the Mesa hardware I'm looking at the 5i23 PCI card and 2x 7i37TA to run the servo's and if it's possible to run the encoders too. I don't have a 0-10v spindle control I think with this setup so I might have to do something very soon down the road for that. I think I could even just make my own 0-10v card to control spindle speeds and cw/ccw rotation.

So does this seem like I'm going in the correct direction. I almost pulled the trigger on that DMM setup and I'm glad you chimed in. I also found out they also have been known to have a following error. Either way I'm going with what I know works and hoping for the best. Just need the Mesa stuff nailed down before I order the Mesa gear.

Jeremiah