[LUCKY13]

Whats the max frequency or count with quadrature that the 320 can preccess?


I keep hitting a wall without any encoder signal problem and the motors have been tuned on a scope. Not matter what I do it want go beyound this point. The wall seems to be around 110,000 counts per second. I dont know if this is what's causing the wall but there is no noise in my encoder signals, nor do they get week. When I scope both A & B channels nothing gets out of phase and no matter how I tune the motors, or which driver & motor I am tuning it still hits this same wall. The encoder signals are very clean also, it never faults except when it hits this wall.




Jess

[mif73]

Hi Jess, I assume when you say 320 that you mean geckodrive G320 servo drive?
If so, I will try to help you out.
I'm not sure what you mean by hitting a wall, I assume that may mean you get the fault led to light and the drive has to be reset?

The docs that are supplied with the drive specify a max step rate of about 250Khz from the computer etc.
The max position error you can have between command and feedback pulses is 128 pulses, or else the fault led will light.
This can occur because of low power supply capacity, incorrect tuning of the drive, excessive step speed, incorrect accel/decel time constant, or heavy load/weak motor.

Does the problem occur with the motor installed or free running with no load?

What software are you using to provide the step pulses?- have you tried to slow the accel time and or decrease velocity?

I hope this info is on the right track for you , if not let us know.

Good luck.

[LUCKY13]

Hi Jess, I assume when you say 320 that you mean geckodrive G320 servo drive?
If so, I will try to help you out.
I'm not sure what you mean by hitting a wall, I assume that may mean you get the fault led to light and the drive has to be reset?

The docs that are supplied with the drive specify a max step rate of about 250Khz from the computer etc.
The max position error you can have between command and feedback pulses is 128 pulses, or else the fault led will light.
This can occur because of low power supply capacity, incorrect tuning of the drive, excessive step speed, incorrect accel/decel time constant, or heavy load/weak motor.

Does the problem occur with the motor installed or free running with no load?

What software are you using to provide the step pulses?- have you tried to slow the accel time and or decrease velocity?

I hope this info is on the right track for you , if not let us know.

Good luck.

mif73


Yes I am talking about the drive faulting when it hits a wall, and this is on a bench still, not on the mill.


I can back accel/deccel and squeez about 120 counts per second. Of course velocity is directly linked to your rapid speed. If you set velocity to 220, 220ipm is what it wants to run upto.

My system for instance is setup to run a 3 to 1 gear ratio on the motor with a 500cpr encoder mounted on the motor. With this setup at 220imp it has to count 110,000 encoder counts per second (in quadrature). I can squeeze things by slowing down the accel/deccel and get it to run 240imp which will have it counting 120,000 encoder counts per second. This is the very max it will run at no matter how things are tuned. Of course I want more accel than 1 so I chose to run it at 220imp with some accel/deccel.

If I was to set it up with a 4 to 1 gearing ratio on my motors I hit a different max rapid (imp) wall, but it comes down to the same counts per second on encoder counts.

None of these setups will over step the 250khz steps per second limit of the step pulse (if I understand right, I may not). The limiting factor is always the encoder counts per second no matter how I set it up. Lets so I was to run a 2.5 to 1 gearing ratio ( all of these ratios are figured with a 5 pitch screw also) At this setup I would have a max of 260imp (with some accel/deccel). So at 260imp I would figure this


(260/60) = ? x 25.000 = ? The answer would be 110,000 which would be the encoder counts per second . The 25,000 is the counts per inch (BTW I am using Mach3).


No matter what gearing ratio I chose to set the system up with the my rapids limit is controled by the encoder counts per second I can run, 110,000 with steady results and 120,000 with it on the edge. Motor tuning does not effect this, of course i can get to fault at a lower point with the motors out of tune but as long as they are tuned the results are the same. Each motor with all three axis hit the same limit. With the scope all encoder signals are very good, no noise and the signal stays strong. I tried different pulse widths and there was no effect to this limit from 1 to 5us.


Maybe there is something else I am not catching but it seems like its the drive not able to count encoder counts beyound this point. If so a simple change of encoders to a 250cpr could solve it. I would not do this because I would rather have the better ressolution and live with the limits, but I would like to answer as to why there is this limit, or what is causing it. No biggie no matter what is causing it , I just want to understand. One thing I have notcied is others with the same setup as mine hit the same wall if there system is able to push to the max ( big enough power supply and fast enough ability to send the step/direction signals) limits. My system has a 72v 20amp PS and the motors are the HomeShop 850 servos which are rated at 72v. My voltage bever drops below 71.5v on the motor lines. I am running a SmoothStepper which can give very fast step/direction signals but with my 3 to 1 gearing on the motors I only have to run it at 128khz for it to keep up so I don't feel like I am surpassing the 250khz limit of the drive. I can set the SS to 250khz but there is no use with this setup, you only lose res of velocity updates if I do that.


Thanks Jess

[TOTALLYRC]

Max on those motors is 140,000 counts per second based on 4200rpm and 2000 ct/rev. This is optimum based on their specs from the website and the kv ratings on the motors.

Then remember, that when installed, the motors will not go this fast as they will have to move a load.

Remember that 1 encoder count is equal to 1 step from the software unless you are using a step multiplier like the G340.

I think what you are describing as the wall is not the limit of the g320, but the limit of your motor to follow the g320 commands and then when the motor gets more than 128 steps out of position, the drive faults.

4200rpm*2000steps/rev= 8,400,000 steps/min / 60secs/min=140,000steps per sec. This is the maximum steps per sec that the motor will accept if it runs at 4,200rpm at 72 volts. You are pretty close to this at 120,000. Not every motor will go exactly the same rpm on the same voltages and I would say you are within the tolerance at 120,000 per sec.

3 to 1 * 5tpi * 2000step/rev= 30,000 steps/inch.

The absolute max that these motors will go is 280 ipm with a 3 to 1 on a 5tpi screw at 4200rpm under perfect conditions. If my math is correct and I have been wrong before. As soon as you load the motor with mass and friction from the axis, you will go even slower.

It seems to me that you are at the limits of the motors, not the g320

Mike

[LUCKY13]

TotallyRC, I believe you may be right on this. I picked up a different scope ( one I payed for that has been calibrated lately) that works really good. After redoing my electronics enclosure box so I could get to everything much easier for testing I did a lot of testing to find no other reason for the wall. My encoder signals are just rock solid, and in perfect phase at all times. The step direction signals going to the drives showed good results also. My system is just simply noise free at all times. This may change when I get it mounted up on the mill but for now its as clean on all signals as I could ask.


I did get it to go past the wall with the accel/deccel down to number 1. This allowed it to go the full RPM of the motor which wasnt much more than before really. Still its not a tune that could be used. Running pretty good accel/deccel I can still get a good 220ipm out of the system and I expect to be able to get close to that when mounted on the mill (atleast 180ipm). This is pretty good rapids so I am not going to worry with it as long as the system shows to be working like it is.

The HEDS encoders that are claimed to not work very good show very good signal and this is one thing I expected trouble out of. I have even extended the cable to 8ft now and they still work. I have good isolated power running to them. I don't know if that really helps them or not, but the lines are very clean from noise with this setup. I do plan to try some other equipment I have that will allow me to push more encoder counts just for testing later but I don't expect to find anything. I just want to comfirm for sure that I am not being held back anywhere other than reasons that should be. With these motors having a max of 4200rpm its very possible that it is the limit of the motor as you where talking. This being my first system I didn't realize that a motors RPM limit would react this way and I figured it woudl just top out on RPM and not turn any higher. I guess in a sense thats what they are doing but I didn't expect the drive to loose lock when this happens.


If the Gecko drive step pulse freqency limit is 250khz then 250,000 encoder counts per second should be the upper limits if I am understanding this right. I would like to try a higher count encoder on this system, and a little later I will do so. I guess you can get to fine of a resilution but I would like to try one anyway. Of course right now its pretty high res anyway but I tend to try to get all the performance I can get out of machines no matter what they are. I plan to try a couple of different gearing ratios on my motor belt drives so I will wait until I settle in on a ratio before I go any farther.




Jess

[TOTALLYRC]

Hi Lucky13,

It is nice to see that you are taking a very reasoned approach and not just saying that the drives are no good.
I am happy to see that the HEDS modules that you are using are working for you. All three of mine had to be replaced to get the machine rock solid.

When you said that the motor would top out and you didn't realize that the drive would lose lock, your original post was the first time that I thought it all the way through. It really makes sense because the motor is supposed to run in lock step with the drive at all time and if you get outside of the error window, then it faults.

Out of curiosity, with the 8' cable, were you scoping the signals at the drive where it would be weakest or at the encoder?

Keep up the good work.

Mike

[LUCKY13]

TotallyRC I scoped at both ends. This was one of the reasons I redid my enclosure box was so I could get to any where I needed to test. Now no matter what I wish to test I can get to it without taking anything apart.


I did try to add bypass capacitors to see if there would be any change. To be honest this was when I was still looking for what was causing the wall, but never the less it did not help the encoder signal any. It didn't hurt it any either though.


There was no difference in the signals on the encoders between 6ft & 8ft cables, but I have went to extremes to try and eliminate any possibility of noise getting in. For instance all my signal lines are enclosed in a metal box except for a little bit that runs up and goes to connectors to bring them outside. I may wrap this little section with foil tape just to make sure its all shielded extra good. When I get the camera back I was using I will post pics of the enclosure in my build thread so you can see what I mean. I am also going to try and post pics of the scope with all the signals and tuning.


I am not sure why these encoders are working so good for me. The cables are just what US Digital sales for them and the cable I extended them with is nothing more than the cable out of old KeyBoards that I salvaged and used. I used the same for the step & direction lines and both them & the encoder lines go right off the drive and turn down to go through a grommet to go into the metal box it runs through. The power wires run off the drives out in the open but everything else is away from them. I do have some special lining that is made to block noise I have used also, it was salvaged out of old copier machines where they had the mother boards isolated to keep noise out of them. I installed a line filter on the A/C side right before it goes to the main power supply and it also was a piece I salvaged off a copier. Copiers are very sensitive to noise and when you go service them one of the first test the OEM factories have you do is test for noise on the main line before you are aloud to go any farther with any repairs.

All these little extra steps & parts I used may be helping to keep the noise out of the signal lines. But again I may put the system on the mill and find I have problems that I am not aware of yet. It should not be to much longer and I will get to find out, but for now I feel like I have done all I can do to help it.


I hope I wasn't sounding like I was jsut kicking on the drives with my thread. Its not my intention in anyway. Although I will be the first to admit I am not very good with writing or know how to say things. I only wish to get my system working the best I can and I'm afriad that I just want settle for "OK its working" or " OK this must just be my limits". I want to know why, and how. I feel like the better I understand the system the more chance I will have of knowing whats wrong when something does happen. Just starting out I find its nothing to learn something new almost everyday about CNC or the machine. I don't expect this will slow up anytime real soon either and I will probably chase something that turns out to be wrong many more times before I have success with this machine.



BTW thanks for your imput on the subject. Unless something else turns up (and I don't expect it to) I feel pretty sure that you nailed the reason for the limit I was hitting. I find no other reason either.

I am very glad I found a good scope to help with my build and even though it adds to the cost of building a machine I would suggest anyone building one to pic up atleast a small scope to work with. The scope answered a lot of questions for me & when it comes to tuning motors there is not much difference between tuned and not tuned. In other words you could get the motors running good without a scope, but the tune would not be anywhere close to being right. Not that you cant get by without one but you really can have it way out and still have the motors running faily good. If nothing else tuning with the scope may help the motors & drives last better, and I am sure it will help the machine cut better even if it is on some small level.



Jess

[TOTALLYRC]

Hi Jess,
I was not suggesting that you were going to chuck the drives, it is just that so many people, my self at times, will just say it must be bad hardware and I was giving you kudos that you were taking the time to ask questions and figure it out.

I agree if you can afford one and know how to use it, a scope is a great idea. I have a heathkit scope that has helped out a few times but it seems that I need to send it out for repair as the last time I used it it was acting funky. You may have a different version of the encoder module but what aever the reason it is great to see that you are having succes with your machine build.

Mike

[LUCKY13]

No problem, I just didn't want any one that was reading to take the post as such.



I have a very nice HeathKit scope here that looks like brand new but its got problems also. I don't know why but I always kinda liked this older 70's electronic stuff like this and I am hoping to be able to fix mine when I learn a bit more about this electronics game. The driver transitors seem to be bad but I believe it has some caps giving problems also. Getting these old parts seems to be a bit hard but I was going to start buying up parts and tackle fixing it when I am more capable. Its in so nice a shape I tried to get a local elctronics guru to fix it for me but he stays so busy he didn't want to put his time into this because he knew it could get into more time than it was worth to fix it. I would like to get a good sevice manual for it but its not anything I am in a hurry about so for now I have just packed it up to keep its cover and face in the nice claen shape its in. You open it up and it looks something new from back in its time so I feel like its worth fixing even if it takes me some time.


The scope I am using right now is a Secore SC61 that was used in a repair shop and the calibration was keep up with checkups every year. I have a lot to learn before I can make good use of it but its pretty simple getting these readings for what where working on with the CNC stuff. One reason I bought it is because I knew it was keep up good and the other scope I was using is the exact same thing so I kinda have spare parts incase its needed.


I don't know a whole lot about electronics but I have been putting a lot of time into trying to learn. I have started out with one of these pic kits that you can do many little projects with and it helps to learn the hardware plus the software side of things. The math is whats really hard for me and I am a bit slow at learning things like this anyway. Still it helps keep my mind busy and its not a bad skill to be knowing something about. There is just so much envolved with electronics though I don't expect to get very far with it but I do enjoy it so I keep trying.


If you have any info on the HeathKit scope I would be interested in it. I don't really need the scope now but I hate to see it go to waste. If it turns out to be beyound repair the case will make a nice power supply case but if I was to go down that road I would salvage the parts for anyone needing them. I have found a schematic but not a manual, and most of the info I have found with people trying to repair them say the transformer shorts out in them. I have not tried to test anything for now because I have enough other stuff going on but I got the probes that go to the scope and like I said it looks very nice. Its more of a interest in trying to fix it than a need though so I will let it set for now.



Jess

[keebler303]

You can see if you have reached the motors max speed by putting the scope on the motor leads. You should see the PWM signal. As you speed it up, the duty cycle will increase. You are at full speed when the duty cycle is at or near 100%. If your acceleration value is reasonable and the drive faults when the duty cycle approaches 100%, this is almost certainly the problem. You are telling the G320 "faster, faster" and it says "I am going as fast as I can" and then it faults. You are not supplying enough voltage to go any faster than that. Try using half the supply voltage and you should see the drive fault at about half the step rate you are seeing now.

Matt

[LUCKY13]

You can see if you have reached the motors max speed by putting the scope on the motor leads. You should see the PWM signal. As you speed it up, the duty cycle will increase. You are at full speed when the duty cycle is at or near 100%. If your acceleration value is reasonable and the drive faults when the duty cycle approaches 100%, this is almost certainly the problem. You are telling the G320 "faster, faster" and it says "I am going as fast as I can" and then it faults. You are not supplying enough voltage to go any faster than that. Try using half the supply voltage and you should see the drive fault at about half the step rate you are seeing now.

Matt

Thanks Matt.

I feel like we have indead reached the motors limits. I mean lets face it the motors are not going to run any faster than they are spec for. Until I mount the system on the mill itself and see where things fall I am just going to let it be. Although I will run this test just to see what I find. But as long as the motors perform close to what I know they should do there is not much I a can do to help them. I have seen these motors run at 3300rpm on a mill that is bigger than mine so I should be able to reach this level anyway. This would put me at 220ipm rapids with great response out of the table movement so it should be quit good if it does infact reach this. This would be with a 3 to 1 gearing and the motors might just have enough power to run something like a 2.5 or even 2 to 1 gearing which would give me even more rapid speed. It all depends on how it runs though because I want give up any response out of the system for rapid speed. I will just have to wait until I am mounted on the mill to answer these question.



Jess