Are these the type of SERVO I would need should I decide to go the servo route?
What are the disadvantages of going servo rather than stepper? Just cost? Or are they much more complicated?
3 servos
CNC servo?
Moderator: Harold_V
Re: CNC servo?
Hi Jerry,
Very questionable?
These servos would be fine on a light duty machine. I doubt any good for a Bridgeport size mill. I don't have time right now to convert the 44oz-in/amp to see if that hold true.
25lb/inches would be the range to look for. 140volts at 8 amps is what I see on average. That works out to be about 1100+ watts or better than 1 hp at the shaft, not including any mechanical advantage from pulley ratios to the leadscrew.
Most of the systems I have worked on run the servos at 90 volts, but can go as high as 180volts.
DC
Very questionable?
These servos would be fine on a light duty machine. I doubt any good for a Bridgeport size mill. I don't have time right now to convert the 44oz-in/amp to see if that hold true.
25lb/inches would be the range to look for. 140volts at 8 amps is what I see on average. That works out to be about 1100+ watts or better than 1 hp at the shaft, not including any mechanical advantage from pulley ratios to the leadscrew.
Most of the systems I have worked on run the servos at 90 volts, but can go as high as 180volts.
DC
Re: CNC servo?
Doug,
I checked out AH-HA and according to them, steppers are better in some ways because they do not need to give any kind of feed back to the computer. The servos are better in the area of acurracy because they have feed back that tells tne computer just how may revolutions the motor has turned as well as the exact location of the bed in referrence to the start point.
I am seriously thinking (there I go thinking again) about stepper drives now rather than servos. They seem to offer simplicity as well as power.
Speaking of power....I notice that power feeds have 135-150 in-oz of torque. Some of the steppers claim they have 600 in-oz of torque. Do I not need this much torque or is it better to have a lot of torque availible but not used? Do I look for motors with a lower torque rating in order to cut down on the amount of amps and volts needed to do a given job?
Ah-ha mentioned a size 34 motor that produced several hundred in-oz of torque with a .625 shaft size. Should I look for mounting size/shaft size as an indication the motors potential or am I just going about this all wrong?
I checked out AH-HA and according to them, steppers are better in some ways because they do not need to give any kind of feed back to the computer. The servos are better in the area of acurracy because they have feed back that tells tne computer just how may revolutions the motor has turned as well as the exact location of the bed in referrence to the start point.
I am seriously thinking (there I go thinking again) about stepper drives now rather than servos. They seem to offer simplicity as well as power.
Speaking of power....I notice that power feeds have 135-150 in-oz of torque. Some of the steppers claim they have 600 in-oz of torque. Do I not need this much torque or is it better to have a lot of torque availible but not used? Do I look for motors with a lower torque rating in order to cut down on the amount of amps and volts needed to do a given job?
Ah-ha mentioned a size 34 motor that produced several hundred in-oz of torque with a .625 shaft size. Should I look for mounting size/shaft size as an indication the motors potential or am I just going about this all wrong?
Re: CNC servo?
I like servos because they are smoother and they happened to be available to me. Those servos should be fine. The shaft size really doesn't have alot to do with it. The PMI servo disks I have are less than 1/2" shaft and produce over 1000 in oz. of torque. (The servo disks are non-cogging. they run smooth down to 1 rev per day. try that with a stepper!!) I'd rather have too much torque than too little, but I suppose if it was too little, but still moveable, you wouldn't be able to over feed it, but some materials require high feed rates to produce a decent finish. The motors on the auction come with encoders, so there is no additional cost there. The main problem with servos is if you buy them they tend to be very expensive. Usually on the order of $500 each, (That auction appears to be 450 for three, but I didn't really dig to verify it.) Also in some ways the drivers are easier, in someways harder. They tend to be PWM type controllers vs, full on on a given channel, but you don't have to rotate through the channels. It really doesn't matter, the motion control chips can do all the work for you, it's just a question of how many High current FETs are required. If you are buying drives like Gekos, then that doesn't matter either.
Maybe I should put that other CS-500 PnP machine up for sale... Gantry style x-y table, 5 servos and amplifiers, currently functional if you want to go into SMT board production, but it doesn't hold a candle to the newer stuff... Right now I'm playing with the guts of it's partner.
Maybe I should put that other CS-500 PnP machine up for sale... Gantry style x-y table, 5 servos and amplifiers, currently functional if you want to go into SMT board production, but it doesn't hold a candle to the newer stuff... Right now I'm playing with the guts of it's partner.
Don't take life seriously, it's not permenant
Re: CNC servo?
That is right Jerry,
Steppers do not need feedback. Problems arise when they lose position when you least expect it. Say after a run of parts are complete and most are found to be out of tolerance by .03 and/or shows up as accumulative error. With steppers it is not a matter of if. It is when and will you catch it every time?
In servo applications the control tracks the encoder pulses to count by .XXXX resolution. Not primarily the revolutions. The parameters tell the control how to scale those pulses to the lead screw and pulley ratio in common engineering units. There can also be a compensation table to correct for errors in the Ballscrew pitch, inch for inch.
Both servo and steppers use a home position to establish limits in travel. They also both have user set zero points as incremental reference to paths for current in use geometry.
I may have jumped the gun on questioning those servos. After looking at the conversion for 600oz-in=37.5lb-in. So I guess those may be just fine. They have no rating as to the max amp draw listed, so that is not a fair comparison. Conversely, I have not checked my facts as to actual applied voltage of the motors I was looking at in order to assist you. I was reading the specs directly off the motors we have visible.
2 different ones I see 26 & 40lb-in.
Max volts 140
Torque 26 or 40lb-in
8.6 amps max
I liked the versatility of the motors you are looking at as to functional driven as either step or servo. At least they have the capability to have feedback with the encoders installed.
I have always been a little confused in the torque ratings of motors as displayed by different manufacturers. Some call them out as in-oz, oz-in, lb-in and in-lbs. As far as I know, they are not equivalents. My interpretation of this is that 135oz at 1" is not the same as 1oz at 135 inches. Even so, I think I'd be need'n s'more learn'n to prove it in side by side taste test. [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]
I would not say you are going about it wrong a'tall. Asking the questions before leaping head first is by far the best way to benefit from the learning curve of others willing to help. There is the chance that you could be mis-informed, but not intentionally.
Ehhh....What do we expect for free?[img]/ubb/images/graemlins/shocked.gif"%20alt="[/img]
In the end, as long as you understand the limits of what you put together, it will serve your needs or you will change it.
DC
Steppers do not need feedback. Problems arise when they lose position when you least expect it. Say after a run of parts are complete and most are found to be out of tolerance by .03 and/or shows up as accumulative error. With steppers it is not a matter of if. It is when and will you catch it every time?
In servo applications the control tracks the encoder pulses to count by .XXXX resolution. Not primarily the revolutions. The parameters tell the control how to scale those pulses to the lead screw and pulley ratio in common engineering units. There can also be a compensation table to correct for errors in the Ballscrew pitch, inch for inch.
Both servo and steppers use a home position to establish limits in travel. They also both have user set zero points as incremental reference to paths for current in use geometry.
I may have jumped the gun on questioning those servos. After looking at the conversion for 600oz-in=37.5lb-in. So I guess those may be just fine. They have no rating as to the max amp draw listed, so that is not a fair comparison. Conversely, I have not checked my facts as to actual applied voltage of the motors I was looking at in order to assist you. I was reading the specs directly off the motors we have visible.
2 different ones I see 26 & 40lb-in.
Max volts 140
Torque 26 or 40lb-in
8.6 amps max
I liked the versatility of the motors you are looking at as to functional driven as either step or servo. At least they have the capability to have feedback with the encoders installed.
I have always been a little confused in the torque ratings of motors as displayed by different manufacturers. Some call them out as in-oz, oz-in, lb-in and in-lbs. As far as I know, they are not equivalents. My interpretation of this is that 135oz at 1" is not the same as 1oz at 135 inches. Even so, I think I'd be need'n s'more learn'n to prove it in side by side taste test. [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]
I would not say you are going about it wrong a'tall. Asking the questions before leaping head first is by far the best way to benefit from the learning curve of others willing to help. There is the chance that you could be mis-informed, but not intentionally.
Ehhh....What do we expect for free?[img]/ubb/images/graemlins/shocked.gif"%20alt="[/img]
In the end, as long as you understand the limits of what you put together, it will serve your needs or you will change it.
DC
Re: CNC servo?
Doug,
I can't argue with the help you and the others are giving me. Free or otherwise, The info is of great value to me and perhaps other beginners as well.
Thank you for your help thus far.
I AM learning believe it or not.
I can't argue with the help you and the others are giving me. Free or otherwise, The info is of great value to me and perhaps other beginners as well.
Thank you for your help thus far.
I AM learning believe it or not.