[NardisAmps]

In short, I think I know the answer......being No.

Here's why I'm asking. Last week I purchased a small (approx 3x3) DIY Router that is very heavily built, with a welded steel frame, heavy ballscrews and bearings, and large 1680 oz/in NEMA 34 stepper motors, driven by industrial drives. The previous owner had also installed a US Digital encoders and a Rogers encoder board, so that if any steps were lost Mach3 would see an error and stop. He was also running the machine at VERY slow rates, like <60ipm on most axis, I suppose because has was only machining aluminum with it.

Now, I have it, and want to increase the feedrates in the 150-200ipm range or higher if possible. But now, for some reason since I have retuned the motor speeds in Mach, as soon as I start to jog any axis the machine throws an error and goes into Reset mode. I assume it's an encoder issue. As large as these motors are for a relatively small machine, should I just bypass the encoders and run the motors without them? Typically if I wanted to deal with encoder issues I would at least have Servo Motors too, but I don't so its very aggravating.

Ultimately the frustration is most likely my lack of knowledge as I have only ever dealt with steppers, and have never dealt with encoders in any combination. So I just want things to work again. Would anyone be so kind as to share their 2 cents? Thanks in advance!!

-Nardis

[louieatienza]

In short, I think I know the answer......being No.

Here's why I'm asking. Last week I purchased a small (approx 3x3) DIY Router that is very heavily built, with a welded steel frame, heavy ballscrews and bearings, and large 1680 oz/in NEMA 34 stepper motors, driven by industrial drives. The previous owner had also installed a US Digital encoders and a Rogers encoder board, so that if any steps were lost Mach3 would see an error and stop. He was also running the machine at VERY slow rates, like <60ipm on most axis, I suppose because has was only machining aluminum with it.

Now, I have it, and want to increase the feedrates in the 150-200ipm range or higher if possible. But now, for some reason since I have retuned the motor speeds in Mach, as soon as I start to jog any axis the machine throws an error and goes into Reset mode. I assume it's an encoder issue. As large as these motors are for a relatively small machine, should I just bypass the encoders and run the motors without them? Typically if I wanted to deal with encoder issues I would at least have Servo Motors too, but I don't so its very aggravating.

Ultimately the frustration is most likely my lack of knowledge as I have only ever dealt with steppers, and have never dealt with encoders in any combination. So I just want things to work again. Would anyone be so kind as to share their 2 cents? Thanks in advance!!

-Nardis

It would help to know what drives are used, if there's a separate power supply or integrated into the drive and if so what is the output voltage. Information on the pitch of the leadscrews, microstep settings, may help. Typically these larger steppers will lose torque rapidly as the speed increases, and likely needs a larger power supply to drive them faster at torque. In fact this is not an uncommon problems there are many builds here were oversized steppers were used, typically with underpowered PSUs, resulting in lower rapids. Of course for the previous use of the machine, this may have been fine.

My best guess is that you probably could use smaller NEMA34 steppers...

[ger21]

A properly set up stepper system should NEVER lose steps. If you're using encoders to stop the machine if it loses steps, then the real problem is that your trying to run your machine faster than the motors are capable of moving it.

I think the main problem your having is that your steppers are far too large. Every machine I've seen with those big steppers performs very poorly, because those steppers just can't spin very fast. I've seen cases where 1600 oz motors were replaced with 400oz motors, and performance increased by 5x or more.

What size are your ballscrews? Diameter and Pitch?

[Hytek]

I think louieatienza has pretty much covered the issue of the motors throwing a reset error but I would like to add my 2cents on the encoder side of your post. Steppers without encoders are like a one way conversation. Mach3 in your case tells the drive to tell the stepper what to do. Beyond that Mach3 can only assume the stepper has done its job and continues to give orders oblivious to any change in condition. With encoders however Mach3 knows exactly what is going on and any unforeseen mishaps can be quickly rectified and you can get back on track with little to no signs of error. The encoders will also improve the machines repeatability. So if you have the time and can muster up the patience I think you will be happier with the encoders operating

[ger21]

With encoders however Mach3 knows exactly what is going on and any unforeseen mishaps can be quickly rectified and you can get back on track with little to no signs of error.

Even with encoders, Mach3 has no idea what the motors are doing. The only way to use encoders in Mach3 is to use a macro or plugin to monitor the encoder position, and stop the machine if it's out of position. As I said, a properly designed and setup system should never lose steps. There are thousands of stepper machines running with no encoders. If they were losing steps, they'd be pretty useless.

The encoders will also improve the machines repeatability.

No, they won't. Unless your machine is constantly losing steps. If that's the case, encoders should not be the first solution.

[NardisAmps]

It would help to know what drives are used, if there's a separate power supply or integrated into the drive and if so what is the output voltage. Information on the pitch of the leadscrews, microstep settings, may help. Typically these larger steppers will lose torque rapidly as the speed increases, and likely needs a larger power supply to drive them faster at torque. In fact this is not an uncommon problems there are many builds here were oversized steppers were used, typically with underpowered PSUs, resulting in lower rapids. Of course for the previous use of the machine, this may have been fine.

My best guess is that you probably could use smaller NEMA34 steppers...

Thanks for the input guys! I'm still new to all this so your help is much appreciated. The drives have the power supply integrated. It appears the voltage is 160v with a selectable current of 0.1-6.0 amps. I have attached a PDF of the drives I am using. They look fairly substantial, but as mentioned it's gonna be relevant to the motor size, so they may be mismatched for all I know.

[louieatienza]

Thanks for the input guys! I'm still new to all this so your help is much appreciated. The drives have the power supply integrated. It appears the voltage is 160v with a selectable current of 0.1-6.0 amps. I have attached a PDF of the drives I am using. They look fairly substantial, but as mentioned it's gonna be relevant to the motor size, so they may be mismatched for all I know.

A sampling of 1600in-oz steppers I've seen on eBay have an inductance of 22mH. Using Marriss at GeckoDrives formula for max voltage comes to around 150VDC. Which leads me to believe intially that should be fine. Then again, I have a few sets of Parker Compumotor stepper motors and drives, where the steppers are 280in-oz and the drives are rated at 170VDC.

There is an issue I recall with servos and US Digital HEDS encoders, where a resistor and cap were piggybacked into the encoder connector as a sort of filter; it might be in the metalworking section. Steppers and encoders are probably pointless anyway unless you're using a drive designed specifically for the application, like Leadshine's step-servo system. And they do have them in NEMA34 sizes, though I believe they use 3-phase steppers in their setup. You can try disconnecting the encoders and see what happens.

The second thing is, not knowing what your microstep settings are, you can try a lower resolution, especially if you have a finer pitch screw. Increasing the resolution can give you smoother movement, but it comes at a cost of torque. You'll get greatest torque at full step, and maybe 70% at half-step. If you're using the parallel port on your computer and you have a high step count it can cause problems, or if you're running off a laptop. You don't mention what controller you're using (Mach3, EMC...) You also don't mention what accel settings are. Again knowing what diameter and lead of your ballscrws can help with determining what's going on.

It might not be a bad idea to purchase a smaller NEMA34 motor, maybe no more than 600in-oz, to see if that helps. Larger motors typically have a larger inductance, meaning it takes longer to charge up the coils, which decreases performance. This is one reason why the smallest motor that can "do the job" is typically selected. But since you already have the machine, and you should be able to calculate approximately how much force would be needed to move each axis at the desired speed and taking the ballscrews into consideration figure out what size motors you really need. I believe Kollmoregen and Lin Engineering have free calculators for this. The GeckoDrive website also gives a tutorial on estimating torque needed.

[ger21]

A sampling of 1600in-oz steppers I've seen on eBay have an inductance of 22mH. Using Mariss at GeckoDrives formula for max voltage comes to around 150VDC. Which leads me to believe initially that should be fine.

Keep in mind that Mariss' formula is for the maximum voltage of a particular motor. Even at their maximum voltages, there will probably still be a substantial difference in usable rpm between a 400oz motor and a 1600oz motor. Even at 500rpm, the 400oz motor may have more torque than the 1600oz motor.

[NardisAmps]

Even with encoders, Mach3 has no idea what the motors are doing. The only way to use encoders in Mach3 is to use a macro or plugin to monitor the encoder position, and stop the machine if it's out of position. As I said, a properly designed and setup system should never lose steps. There are thousands of stepper machines running with no encoders. If they were losing steps, they'd be pretty useless.

That's what I had understood to be the case. As it is now the motors want to run, but the encoders keep tripping the Mach3 Reset as soon as any axis starts to move. I don't think it's a motor tuning issue at this point. So my first step will be to ditch the encoders. The machine is currently set up using the "Sound Logic Encoder Interface" from Rogers Machine. I tried to switch off the Encoders in the Encoder/MPG tab under the Ports & Pins Config menu in Mach3, but this did not do it.

What do I need to do in order to disable the encoders as if there were never there? Is there a Plug-In or Macro I need to remove also? Or am I just not in the right menu? Thanks again guys.

[ssutton]

I would have to agree with Gerry (not that he needs any qualification), I had never to my knowledge had my machine lose steps. Even on jobs that last several hours the machine always is accurate and I am using nema 23 motors and I cut aluminum almost exclusively. The only time that I would consider using encoder feed back for closed loop operation would be with servo motors. I set up servo systems at work and there are distinct advantages to servo systems over steppers, but with what most of us are doing with our machines steppers work out very well.

Scott

[Hytek]

Ger21, I don't disagree that a properly set up the stepper system won't or shouldn't lose steps. Sometimes things just plain and simply happen and if he already has the encoders, why not make use of them. The original question was 'Is there really any advantage to using encoders?' And the answer to that is yes. Does he NEED to run them? Not really. Will his system function adequately without them? Of course it will.

Also note the term 'my 2 cents' is just another way of saying my opinion. My opinion is all I offered and it's on a take it or leave it basis.

[louieatienza]

I 've had a few instances where I've run my spindle into a clamp, or hit a fixture or bolt by accident, or rammed my carriage into the table, and lost steps. Sure under normal cutting it doesn't happen; but it does.

Also, I should clarify - I don't think having encoders is a useless thing, though having a drive that can utilize it to its fullest helps. Check this out:

Leadshine Closed loop stepper - YouTube

[dbsharp]

I have closed loop steppers, I think they are worth the extra money. My machine can run tool paths at speeds that would make my old open loop steppers **** a brick. I was able to tune the open loop steppers so that they all most never missed a step, but every once in a while I would run a program that would cause missed steps and I would be pulling out my hair.

[NardisAmps]

Interesting video louieatienza! Although, now I'm even more confused......how you stall the motor while its running, even for a second, shouldn't that prompt an error with the encoder? Is there a difference between the way closed-loop proprietary stepper / driver sets work (like the Leadshines) vs. regular steppers, say powered by Geckos, with encoders added?

[mactec54]

Interesting video louieatienza! Although, now I'm even more confused......how you stall the motor while its running, even for a second, shouldn't that prompt an error with the encoder?

Confused I think anyone that knows how an out of position Encoder should work, would know It should of stopped with an out of position alarm, within a few micro seconds, it just shows you that it was not doing a very good job, if it was cutting a part, & that happened the cutter or job would be messed up

Doing a stepper system with a closed loop, would cost almost the same as a servo system, & never be as good

[691175002]

This is kind of a loaded question because the terminology is so vauge for most of these products.


Putting an encoder on the back of a stepper motor and using the encoder only to know when the stepper has missed steps isn't that useful IMO because knowing a part has been scrapped doesn't really help that much. Sure, you avoid the occasoinal Z axis failure that will smash a drill into your vice, but on the whole you end up spending a lot of money for a marginal advantage.





None of the "hybrid stepper" systems have much to do with a traditional stepper motor. They are servo systems by every definition, and the marketing clowns decided to call them steppers instead. As soon as you use feedback for commutation, it is a servo. In fact, some of the "hybrid stepper" systems even use three phase motors!

From a technical standpoint, brushless motors and stepper motors are actually almost identical in construction, and the primary difference is that stepper motors have very high pole counts (so each "Step is a very small angle) whereas "normal" brushless motors have lower pole counts (and each step is a larger angle).

The pole count is the electrical equivalent to gearing, and this is the reason why stepper motors have low RPMs but high torque, and servo systems generally run at high RPMs but require belt reduction or gearing to produce enough torque.


A "hybrid stepper system" is just a brushless servo with a high pole count, or equivalently a stepper motor attached to servo electronics. The advantage of a high pole count is that you can direct drive since you get a lot of torque. The disadvantage of a high pole count is the RPM is limited and you lose some efficiency.





I wouldn't really say that hybrid steppers are much cheaper than a typical servo setup, because you can get chinese AC servos at comparable prices.

[louieatienza]

This is kind of a loaded question because the terminology is so vauge for most of these products.


Putting an encoder on the back of a stepper motor and using the encoder only to know when the stepper has missed steps isn't that useful IMO because knowing a part has been scrapped doesn't really help that much. Sure, you avoid the occasoinal Z axis failure that will smash a drill into your vice, but on the whole you end up spending a lot of money for a marginal advantage.





None of the "hybrid stepper" systems have much to do with a traditional stepper motor. They are servo systems by every definition, and the marketing clowns decided to call them steppers instead. As soon as you use feedback for commutation, it is a servo. In fact, some of the "hybrid stepper" systems even use three phase motors!

From a technical standpoint, brushless motors and stepper motors are actually almost identical in construction, and the primary difference is that stepper motors have very high pole counts (so each "Step is a very small angle) whereas "normal" brushless motors have lower pole counts (and each step is a larger angle).

The pole count is the electrical equivalent to gearing, and this is the reason why stepper motors have low RPMs but high torque, and servo systems generally run at high RPMs but require belt reduction or gearing to produce enough torque.


A "hybrid stepper system" is just a brushless servo with a high pole count, or equivalently a stepper motor attached to servo electronics. The advantage of a high pole count is that you can direct drive since you get a lot of torque. The disadvantage of a high pole count is the RPM is limited and you lose some efficiency.





I wouldn't really say that hybrid steppers are much cheaper than a typical servo setup, because you can get chinese AC servos at comparable prices.

I've seen Leashine's "300W" Easy Servo motor and drive kit (with cables) for under $220 on eBay. You'd be hard pressed to find an equibalent servomotor for that price. Also, for most applications there's no tuning necessaey.

[mactec54]

I've seen Leashine's "300W" Easy Servo motor and drive kit (with cables) for under $220 on eBay. You'd be hard pressed to find an equibalent servomotor for that price. Also, for most applications there's no tuning necessary.

Dmm AC servo system would be close to the same price for that size, servo motor drive kit

The same with the Dmm AC Servo Drives there is basically no tuning to do

DMM TECHNOLOGY CORP.

[amaldo]

What I've found is that the cost of a "hybrid" stepper (with encoder) together with its controller is similar to a servo system, but the servo motor will usually need a gear to increase torque. If you go with a nice planetary gear with low backlash , they can easily cost 200-300 USD. That makes the servo systems always more expensive. But I'd love it if someone can show me I'm wrong on this one.

[mactec54]

amaldo

Gearing is a myth, if the servo is sized correctly no gearing is needed, you only use gearing if you have a small servo motor trying to move a heavy load that is to much for that size motor

A servo has a rated torque & a max torque

A stepper has a rated torque

With a servo, if it needs more torque to get moving, then it will use what ever it needs, up to it's max, to get the job done