Boss 5 Upgrade

[Meenbombs]

I have scoured all of Google over the last few months and convinced myself to do this one way only to convince myself the next day to do it the other. I have a few questions that might cement my plan and would appreciate anybody that could help.

Mach3 vs EMC2
I originally was slanted toward Mach but despite it being generally pretty stable it seems by a lot of posts to be more glitch/freeze prone than EMC2. It may be Windows vs Linux but the reason doesn't matter when $100 worth of aluminum is cut wrong. Am I off base here? From what I can tell the EMC2 setup is more challenging but after that it works just as well as Mach and more stable.

Stepper vs Servo
I am fairly certain servos are the way to go but in 2011 they are not better by the margin they used to be and probably not worth the cost for all but the most demanding application. I wouldn't think I would have any issues with steppers if I used 1200 oz/in steppers and an adequate power supply. However, do servos have any better resolution? I have read they are faster but I don't care much about that as I am not doing any long production runs.

So I am leaning toward EMC2 with 1290oz steppers (RS34-1290D) I wanted to run Gecko drives because I haven't seen anything bad about them but the motors draw 100% of the drives rated output. That isn't good for the drive but I am pretty sure I will be underutilizing the motors so they shouldn't be drawing the full 8 amps. Any advice on this? Am I good with the Geckos or should I be looking elsewhere.

I am looking at the C11G available at CNC4PC for a BOB. Does anybody have feedback on that board or suggestions for a better one?

Thanks in advance for any help.

Also, I do a lot of custom work in aluminum. I might do steel once in awhile and a large production run of anything would be 25 pieces so this isn't a very demanding application but I don't want to tie my hands in the future either.

[sdeering]

I use Mach 3 you can down load it and trial it for free maybe you can with emc2?

I find for me the simpler the better. and Mach is pretty simple. The problem with trying this and that it takes a lot of learning to make things work which is time wasted.
THe drawback with steppers is no feedback but they are simple to set up. Cost may be a factor as well as with maintanance. no brushes in steppers.

Wish I could be of more help.

Good luck.

[HawkJET]

Mach3 vs EMC2:
I started my retrofit with the intention to use EMC2 but changed to Mach3 because of the superior support from users and forums. I haven't run into any stability problems in over a year of almost daily use. I have heard that there are some glitches in the "run from here" feature where you can restart in the middle of a program. EMC2 doesn't even have that feature (as I understand).

I wouldn't use stability as a major factor in the decision.

Stepper vs Servo:
Using Geckos and servos will work just fine but there is not much difference than using steppers. Since Geckos use the same step and direction pulses as steppers, it is a limitation of the true advantage of servos. EMC2 and servos would be the better choice if using servos since EMC2 closes the loop internally rather than depending on the motor controller.

A stepper motor system will also work very well. If you are not looking for that extra speed, you will likely never notice the difference between steppers and servos.

Resolution with a servo is determined by the encoder used. With both steppers and servos, higher resolution will increase the need for a faster processor.

I wanted to run Gecko drives because I haven't seen anything bad about them but the motors draw 100% of the drives rated output. That isn't good for the drive

Why do you think this isn't good for the drive? If the drive is specified to deliver the current, it can deliver the current. Geckos are designed to have sufficient headroom as to be no problem.

I am pretty sure I will be underutilizing the motors so they shouldn't be drawing the full 8 amps.

Stepper drivers are a current source. If they are set for 8 amps, they are always running at 8 amps. If you want to under utilize the motors, you can set the current for less than 8 amps. But then your previous comment doesn't apply.

I am looking at the C11G available at CNC4PC for a BOB. Does anybody have feedback on that board or suggestions for a better one?

I don't have direct experience with this BOB because I made my own, but it is one that is used a lot without issue.

Good luck!

[Meenbombs]

Thank you. Any help no matter how much or how little is appreciated.

[Meenbombs]

Mach3 vs EMC2:
I started my retrofit with the intention to use EMC2 but changed to Mach3 because of the superior support from users and forums. I haven't run into any stability problems in over a year of almost daily use. I have heard that there are some glitches in the "run from here" feature where you can restart in the middle of a program. EMC2 doesn't even have that feature (as I understand).

I wouldn't use stability as a major factor in the decision.

Thank you, that helps.
Stepper vs Servo:
Using Geckos and servos will work just fine but there is not much difference than using steppers. Since Geckos use the same step and direction pulses as steppers, it is a limitation of the true advantage of servos. EMC2 and servos would be the better choice if using servos since EMC2 closes the loop internally rather than depending on the motor controller.

A stepper motor system will also work very well. If you are not looking for that extra speed, you will likely never notice the difference between steppers and servos.

Resolution with a servo is determined by the encoder used. With both steppers and servos, higher resolution will increase the need for a faster processor.

I wasn't sure how to compare "micro-stepping" to a 500 or 1000 or 2000 or whatever line encoder I chose. I couldn't find anybody with an easy to use chart and I am horrible at math so I didn't try it on my own.
Why do you think this isn't good for the drive? If the drive is specified to deliver the current, it can deliver the current. Geckos are designed to have sufficient headroom as to be no problem.

I didn't have insight on the design parameters the Geckos were designed with but very few industries design their electronics to be run at a 100% capacity for any significant amount of duty cycle. I didn't expect the Geckos to be any different but it is nice to know.
Stepper drivers are a current source. If they are set for 8 amps, they are always running at 8 amps. If you want to under utilize the motors, you can set the current for less than 8 amps. But then your previous comment doesn't apply.

The draw (resistance) is what determines that actual current being used. If the motors are being used at 50% they will draw a theoretical 4 amps. Reality dictates that it isn't a true linear relationship but it is close enough in this instance. If I am not maxing out the capacity of the motors they will not be drawing 8 amps. When you set the supply for a limit of 8 amps that means they will supply up to 8 amps and then the voltage supplied will drop until the draw is 8 amps provided it isn't designed to trip a circuit breaker or fuse.
I don't have direct experience with this BOB because I made my own, but it is one that is used a lot without issue.

I want to do the same but don't have the time.
Good luck!

Thank you for the information. I may go back to Mach but I think I am solidified on the steppers now.

[HawkJET]

The draw (resistance) is what determines that actual current being used. If the motors are being used at 50% they will draw a theoretical 4 amps. Reality dictates that it isn't a true linear relationship but it is close enough in this instance. If I am not maxing out the capacity of the motors they will not be drawing 8 amps. When you set the supply for a limit of 8 amps that means they will supply up to 8 amps and then the voltage supplied will drop until the draw is 8 amps provided it isn't designed to trip a circuit breaker or fuse.

This is correct for a VOLTAGE source. Stepper drivers like Geckos are a CURRENT source. If they are set to deliver 8 amps, they will deliver 8 amps and vary the voltage according to what the resistance is. If you are not "maxing out the capacity of the motors"... YES they WILL be drawing 8 amps! If the motors are stopped, they are still drawing 8 amps! (unless the driver has a feature to reduce this on purpose).

8 amps will be delivered up to the point that more voltage is required than is available. At that point, current will reduce and voltage will be constant (thereby reverting to a voltage source).

[Meenbombs]

I stand corrected. I completely spaced the inductive nature of the load. That makes the drive design make sense because the load is 100% at a 100% duty cycle. Thanks for the mental adjustment.

[HawkJET]

My explanation is about the nature of a current source and stepper motors and not about inductance. The inductance affects the time it takes to increase/decrease the current in the coils.

Stepper motors are driven at full current even when it isn't required because there is no feedback to know how much is needed. Unlike a brushed DC motor, increasing voltage to the motor coils doesn't affect its rotation. To rotate a stepper, the coils must be energized in sequence. It is the rate of the sequencing that determines the rate of rotation. The current that energizes the coils is what determines the torque the motor can exert when rotating.

[Sparky_NY]

I had a bridgeport running under mach, with a C11G breakout board and stepper motors. I had no complaints at all. I came across a deal I couldn't pass up on a bridgeport cnc with servo motors so retrofitted that and got rid of the first machine. The servos are about 3x as fast and do position more accurately.

All the above posts are good correct information but there is a couple things not mentioned. First, the cost difference between a servo and a stepper setup is minimal. If you use something like gecko servo drives and kelling nema34 motors with AMT encoders there is little cost difference but a big performance difference. A fellow did a retrofit with that setup and got 350 ipm !!! My stepper machine maxed out at 70 ipm reliably. My bridgeport factory servo machine does 250 ipm presently under mach. Aluminum milling is done at high spindle speeds and high feed rates, feed rates over 70 ipm are not uncommon at all. I would suggest pricing it out both ways, stepper and servo.

Steppers rated torque is at zero rpm, also known as holding torque. Torque drops as soon as the motor starts moving and continues dropping as motor rpms increase. Normally, the larger the motor the faster that torque drop off occurs. When I did my bridgeport stepper retrofit I looked at different motors and decided against the 1200oz variety. 1200oz motors at speeds of 1000-1500 rpm actually put out LESS torque than the 906oz motors I used do at the same speeds. At extremely low speeds yes, the 1200oz motor has more but at higher speeds things change quickly. Direct drive keeps the motor rpms much lower but at the cost of resolution. This is primarily a function of the motors inductance spec for steppers.

[Meenbombs]

Also great points. I have priced it and it is only a couple of hundered dollars in difference. The main thing that scared me away was trying to resolve the gearing/belt teeth. Most servos of a reasonable price seemed to need a ratio change to slow them down and provide the proper torque. What servo specs would I need to drive the table and quill without changing anything that would require machining new housings? I see a bunch of examples online with new housings and belt drive ratios and then I see the Centroid site that shows a direct bolt on. I think the couple of hundered in difference is worth it provided I don't have to completely change the mechanics of the drives.

[Sparky_NY]

Also great points. I have priced it and it is only a couple of hundered dollars in difference. The main thing that scared me away was trying to resolve the gearing/belt teeth. Most servos of a reasonable price seemed to need a ratio change to slow them down and provide the proper torque. What servo specs would I need to drive the table and quill without changing anything that would require machining new housings? I see a bunch of examples online with new housings and belt drive ratios and then I see the Centroid site that shows a direct bolt on. I think the couple of hundered in difference is worth it provided I don't have to completely change the mechanics of the drives.

A servo setup would probably need a 3:1 belt reduction possibly 4:1 to give you a idea. My servo bridgeport has 2:1 BUT those are huge powertron servos with huge torque outputs. The kelling servos would provide similar performance but would need more of a belt reduction, ratios like I mentioned above. You probably could use the same housings and just replace the pulleys for the table, the quill pulley would not be so easy so you would have to just get the smallest motor pulley possible to get the ratio higher.

Here is a video clip showing the kelling motors with gecko drives and what they can do.

http://www.youtube.com/watch?v=78KUDWnz-WU]Big Mill, Moving FAST! - YouTube

[Meenbombs]

Thank you. That is the servo kit I was considering. Can anybody vouch for its quality?