#331
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Pete, you are paying the price for following Mike's ultra conservative advice on stepper motor voltages. Now you are wasting hours trying to squeeze a little more torque out before you loose steps by fiddling with programs and settings.
You would NEVER want your settings to be on the limits just before loosing steps....you always want good headroom there. |
#332
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Gerald,
I would agree easier if I could understand this one thing. Would you be as so kind to help answer this? I will try to leave some good detail in this but I am terrible at conveying thoughts across through text so if you have any questions I will be willing to clarify. My X0 Y0 is always the same location on the table with rare exception. Roughly 381mm in on both axes from the home switch. My hold down system dictates this. With all the programs I have run, only 4 have had issue. Of the 4, 3 I could believe that statement. What has me at a loss of understanding is why the rest will start the program and call M3, goto the tool change spot, go and set the Z zero, return to the tool change position and return to start the program just fine. It is only these 4 programs. And it is repeatable all at the same spots. Another program it is always at the 3rd toolpath M3 call. Let me first note all my programs have at least 5 toolpaths in them. Logically I would think if it was a voltage issue, I would see this in any program at any M3 call but I am not and I verified this many, many times, including the last 2 days. I could believe since Mach is complex that if the tool change is called from a different position other than X0Y0 that would be true but why on the one it is always right from the beginning starting at X0Y0. So yesterday I even changed the X0Y0 to the middle of the table at X1220Y610 and it is still the same programs. This I do know, if I split the programs at the stall point and only output the toolpaths after that point all in one file it will run fine. The one that starts from the beginning I cannot says that because I just output single toolpaths since it started at the beginning. I have not moved the start point of the M3 call for the rest of the programs to move the toolpaths M3 problem location to the X0Y0 controlled start location and try to run those individual programs with an offset X0Y0 to see if the problem would move. The only thing I noticed is that if the steppers are warmed up and velocities are the same that it will run the programs, but I would have to do a better controlled study to fully back this up because I started by running known programs that would run and changing the velocity and acceleration. Changing the Velocity and acceleration only causes the problem with the same 4 programs. That being said. I have not a problem changing the power supply but will this actually solve the problem? I honestly can not give a definitive YES because this should be showing up everywhere under the controlled tests. Your thoughts? |
#333
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Sorry Pete, I have stopped hurting my head with detailed scenarios like this.
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#334
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That is ok Gerald. I have looked at 50V 800W supplies before. I may be making the upgrade. I just find it odd the it is mostly with tool change and the position of the one is always from 0,0,0 and the same programs and cannot get it to replicate in other programs.
The formula 32 * vL = VMAX equals 67.2V so I was looking at the 50V and the 56V |
#335
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So, Pete, I think you're trying to isolate whether you're looking at a pure software bug, or a condition where the software happens to be consistently requesting more torque than the motors can provide at the same place in the program.
One hypothesis is that the software is broken; the other is that you're at the edge of what the motors can produce under their current power supply configuration. How about adding a 10 pound weight to your Y Car, and seeing if it breaks some other programs? That would confirm the hypothesis that it's torque and not software. I agree that you need more voltage, and more is better within the limits of motor heating. Can't see why you would need 800w though. |
#336
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Brad,
I agree that it is a most likely a torque issue. I am only baffled on why only certain programs and why at the M3. Especially with right at the first M3. But only with 1 program. Like I wrote above. The 800 watt is with 5 motors I would be pushing over the limit of a 500W. Now I know that the chances of ever pulling 100% power on all 5 axes at the same time is slim but I would not wish to chance it. 3 at 50V*1.5A=225W 2 at 50V*6A=600W Combined 825W if drawing maximum power |
#337
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I would like to think I would only be around 175W when cutting but rapids would be around 400W. This is based on proportionally looking at what the current draws currently are. I know that is a flawed way to calculate it. The problem exists when I finally get around to adding the 5th axis. I would like to leave wiggle room. Unless someone else has a system with 5 axes and knows their current maximum usage when running rapids.
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#338
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Same fault on same program is not odd. This is consistence. It confirms that something is not right.
I've given up on tranny size talk. if they can afford them over specs, overly heavy tranny, so be it... Its like brute force obsession... no cure for that. Last edited by KenC; Sun 24 March 2013 at 22:52.. |
#339
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Ken, I do hear that 'Size Does Matter', ha ha
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#340
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ya, too big or too small does matter. I'm sure you had never expect a bull dozer winning a Nascar race LOL
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#341
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For me the price difference is just too small compared to other parts cost, so I use 17Amp transformer for 4 x 5A motors, and it's ok for most work, I notice it gets hotter during some 3D work when all motors work combined
What you can find and what gets the job done is the thing to use, for me there are no strict specs when everyone want's to cut corners or is not able do buy something at the right price. Price of a good router bit can be more than a transformer and they get broken on regular basis. Keep that in mind |
#342
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Here is a scenario, probably not applicable to you, that shows how the reality and the theory can be two different things . . . . and needing the theory to to be expanded:
An acceleration of the gantry in the x-direction needs both of the x-motors to apply torque. But, you find that one x-motor is weaker than the other. Think then if the y-car and spindle is near the "weak" motor. Those motors do not have an equal inertia to overcome if the y-car is off the center of the gantry. Even the dust hose from the ceiling affects the loads on the motors - not constant all over the table. Those were two quick "reasons" why two identical commands behave differently in two different programs. There are surely a lot more. |
#343
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Enough to ponder, I just know there is a problem and I am happy with that for now.
Looking at this post from power supplies and this website from Gecko and little too little attention to detail on my part, all my motors have a rating of 1.5mH. Therefore if I am correct this time, with this from the mechmate post "So, where do we go in the range 24 to 80V? Find the inductance of the motor from its specsheet in milliHenry, take the square root of the mH value and multiply that by 32. For example, a motor that is rated 1.5mH needs: 32 x √1.5 = 39 Volt". My motors need 39VDC. But with this from the Gecko Website 20Xs the motor voltage is (all motors wired are)1.4V * 20 = 28VDC So at most I should be at 39VDC with a 500W power if I was looking at the 2/3 concept. I would feel better with a 600W though. I'm I on the right track??? |
#344
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Ken,
The bulldozer would win, crushes all the cars |
#345
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In keeping with my past history, here are the prints for the 7:1 reduction.
I doubt anyone will take this on but here they are. You will have to modify the relief for the stepper motor and the slot spacing for the hold down bolts. Remember the frame size is larger on the ones I modified, yours are most likely a 3.35 frame. I had to use a piece of 0.5" x 3.5" x 0.125" stock drilled and tapped for the front 2 bolts. Before plug welding, completely assemble unit to maintain alignment of the drive pulley. Large gear does not need to be installed for this process, the bearings will do that. Stitch weld in 3 places the bearing retainers for the 6003 bearings. Remember the back must stay flat for the unit to be able to pivot properly. The plates only go together one way. If flipped, the bolt pattern will not line up. They are yours and free. Enjoy. |
#346
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Wait, those are from PK296A2A-SG7.2's originally, right?
Those are exactly what I'm driving (unmodified) from my G540. I started off running them around 35 VDC, but ended up stepping them up to 48 VDC (by winding a new secondary on my toroid to get to my exact target). I don't care what the theoretical numbers say, they run much, much better at 48VDC than they did at 35 VDC, and I don't have any motor heating problems. If I recall correctly, that was the difference between 300 IPM and 500 IPM rapids, and the ability to drive a 1/4" bit in a 3/4" cut through plywood at 100+ IPM without loosing steps. With the G540, I'm limited to 50V, so I haven't experimented with higher voltages. |
#347
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Brad,
That is correct about the steppers. Good to know about the 48V PS. Thanks again. |
#348
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The following deserves a thread on its own, but I havn't the patience to start it....
The likable Mike R actually did major damage to the concept of using steppers for CNC routing. If you followed his conservative ratings you ended up with a CNC that easily lost steps. Most guys only buy their motors, drives and supplies once and then they are locked in to those choices with a big beast of a machine that takes up the garage. It was only when I started multiple machines that I could afford to measure, experiment, push the envelope, mix parts around and then realise that VOLTAGE is critical and needs to be pushed well above the theory put out by the two experts (Mike and Mariss) if you wanted a decent performance from the monster....and still have long life from the motors. |
#349
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Gerald,
From what Brad and you are saying, I should be just fine with the 50V power supply. Correct? You are right about only buying once, that is the reason I converted the gearboxes to try to minimize the losses from the mistake that no one in maintenance should ever forget. Gearboxes have backlash. I know a lot of guys here are using them and do not have an issue, it just really affected my work so I needed the upgrade. After pricing out, it saved me money and gives me a spare stepper. Live, try and learn. Sometimes it is painful though. |
#350
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Brad,
For the record, I run the same as you with Gecko's 203....@56V. Always been happy with speeds and heat really was never hotter than a fresh cup of coffee with the motors. |
#351
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Been running 48v on mine and it has been running almost daily now for over close to two years with no trouble. If that means anything tp you.
Al |
#352
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Use 56V.
Ross |
#353
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That certainly seems like a consensus up there.
I think it's worth noting that the PK296A2A-SG7.2 is kinda a weird animal as NEMA 34 steppers go. It's the small end of the family, and was deliberately underspecified to keep it from tearing its gearboxes apart. So rules of thumb appear to need more bending, because this motor is at one end of the spectrum. The more I think about this - since the other end of the spectrum are those oft-maligned 1200 Oz/In monsters that can barely get out of their own way - the more it's clear that we're dealing with the high-revving motorcycle engine category and not the tractor category here. So it seems natural that these little motors would be more tolerant of being overdriven than their larger brethren. |
#354
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#355
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Sean, Al, Brad, Ross, Heath
Thanks for the information. These posts help me feel better about the power supply but form new questions in my head? So since I will likely use a 50V or 56V power supply, I will have to lower the drive current to control the motor heating if I am reading everything correctly. Now leaning on the 56V side of things. My PK296-F4.5 steppers have more oz-in of torque according to the specs. They already run hotter wired in parallel. I am assuming they will be drastically reduced in motor current to control the heat on it. That throws a curve into calculating a power supply wattage. The fresh cup of coffee remarks have always got me. Number 1) I don't drink hot coffee only iced coffee on occasion in mass quantities so 2) I have to use information from the National Coffee Association which says A Fresh Cup Of Coffee is served at 180°F (82.2°C) to 185°F(85°C). So should the temperature be right at the threshold of the motor limit? |
#356
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You may or may not have to lower the drive current, but if you aren't comfortable with your motor temperatures, then the current is how to adjust. You could also consider running the PK296-F4.5s as half-coil rather than parallel.
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#357
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Brad so you are saying I should be around 180°F then. I just need to know so when I am setting up I do not cross the threshold of what you all are running. You all have machines running so I would trust your temperature readings.
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#358
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I'm not up around 180; that's Sean. Local effects like ambient temperature, drafts, and how much heat sinking you are getting off those huge belt reductions mean that your results will likely differ; I would start off without lowering the amperages, measure the temperatures until they stabilize (or exceed the motor spec / your comfort), and only then lower the amperage if it turns out you have a concern.
I can comfortably rest my hand on my motors for several seconds, and remove it gradually without fear of burns. That is at 48V / 3.5A. |
#359
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"warm" cup....Let me put it this way. I can wrap both hands around the motor and keep them in place and not go "holy moly" that's hot! I am set roughly 3a/56VDC bipolar, I think it's a 22k resistor, thus about 2.3A or so. All going from memory here......
Just a reminder - I had A LOT of extra MASS on my gantry side. 3/16" wall tubing, 48" z-slide and dust collection - didn't skip a beat. My little history lesson contribution. |
#360
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Pete is using a smaller motors, my hunch is that he is better off running the coils parallel, but than again, I don't have a clue of his stepper motor torque characteristics.
On temperature matter, since it is a subjective defination, I took some time to nerrow down the rough guide with some real number. With a IR thermometer, I went around touch & measure thing at various temperature ; the follow is my take:- ""holy moly" its hot" is right around >70C "Warm cup of coffee" "leave my hands on the motor for a few second is 60~70C "leave my hands on the motor forever but uncomfortably" is 50~60C "Comfortably warm" "leave hands on the motor forever""luke warm" is 40~50C "barely warm up" is anything below 40C BTW, my indoor ambient temp is ~38C hot day, ~35C normal day, ~30C rainy days. humidity average 50~80%. |
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