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General Mach Discussion / Re: My CNC build
« on: June 27, 2009, 09:42:18 AM »
Can't wire in parallel- 6.1a draw in parallel mode, and the Gecko G540 is limited to 3.5a Yesterday I added a relay to control the router power on/off from the computer. NICE not having to get up and climb over everything to turn the router on or off. However, there is an issue with the Y axis. I discovered that one end of the lead screw is .035" out of line with the drive end. More tweaking with shims is needed to prevent lost steps on the Y (as this misalignment is causing some binding issues on the lead screw). Concerning the parallel wiring scheme: with the set resistors in place on the G540, will this be sufficient to limit the current draw to 3.5a? I ask this question, because the last thing I want to do is burn out the Gecko drive. I don't know enough about electronic theory to comprehend exactly how the set resistors limit the current draw to the motors. Gecko recommends 1K per desired amp to be used as the set resistors. (I have 3.5K resistors in line at the moment). Keling specs states that the rated current in Bipolar Series mode is 3.05a for these motors, and 6.1a in Bipolar Parallel mode. Do you think that it would be "safe" to attempt the Parallel wiring without risk of damage to the G540? Should I wire 3.5a fuses in each of the motor supply  conductors to prevent damage to the Gecko? Sorry for the long post, but am trying to grasp how best to try the parallel scheme.

General Mach Discussion / Re: My CNC build
« on: June 24, 2009, 08:22:19 AM »
Well.... I got the 48 volt supply, and also changed out the motors for Keling's 906 oz in motors. Wired them up in Bipolar series (even though the specs state 13.3 mH inductance). Now the machine FLYS! I used the Write wizard, to engrave some text in Times Roman Font, and then used the MDI screen to return to X0 Y0 and repeated 100 times with absolute precision! I was able to tune both motors to 76 IPM, and considering that the old motor/power supply setup could not be relied upon for more than about 6 IPM feed rate, I am simply amazed at the results! I have not yet tried wiring these motors half-coil (don't see the need, since all seems to be well now). Thanks for all your help!

General Mach Discussion / Re: My CNC build
« on: May 27, 2009, 03:45:06 PM »
Arizonavideo, I am not sure how to go about measuring torque output and am operating on blind faith alone that the 2.5K resistors are limiting the current to 2.5 amps. I plan to order a 48vdc power supply today, and with connect it as soon as I receive it. I will report the results once that is done. If I am interpreting correctly what is being accomplished by using the center taps and one coil end only, is that only HALF the coil length is being energized.  This did result in an amazing increase in speed, with fewer lost steps. Before trying this, the motors could not be relied upon to turn the screws for even a minute without stalling. The actual rating of these motors is 2a per coil. (So, I am pushing these about .5a above their rated current). I played last night until about 3:00am with the OPEN test file included with Vectric's V Carve Pro software, trying to carve a pocket.  About halfway through the process, I lost steps, (and of course ruined the part). Thus my decision to go ahead and try your suggestion of the higher voltage supply.  Still monitoring the temperature of the driver, and motors. Still only slightly warm to the touch. (Like a kid, I could'nt wait to play, so I still haven't mounted the Gecko to the heat sink). I currently have Mach 3 setup with the default 2500Mhtz. What changes will I need to make, to set the motors to 900 PPS? (My processor is a Pentium IV running at 1.8 Ghtz). The parallel port is set to EPP mode thru the BIOS (per Gecko's instructions). Are you referring to the pulse rate in Mach 3's Motor Tuning screen? What SHOULD the "inductive ring" sound like? Should the motors be free wheeling, or under load when this test is performed? The pocket cut I mentioned above was set up with a feed rate of 20 IPM. However, I set the Manual Overide to 60% from the MDI screen of Mach before starting the code running. (For an effective feed rate of about 12 IPM). And even at this snail's pace, it managed to lose steps halfway through the code. I do not have an automatic tool changer on my machine, so I stripped out all macros which were generated by the Postprocessor of V Carve Pro. I also do not yet have a touch sensor for setting the tool height, so I manually jogged the tool to the work, recorded this measurement with a back up device (pencil), and manually coded the Z movements to accommodate for the cut depths, and rapids (using notepad's search and replace function). This yielded EXCELLENT results up until the machine lost steps. I am very hopeful that the higher voltage supply will cure this problem. Thanks for all your help, I will be waiting for further instructions on the Gecko adjustments.

General Mach Discussion / Re: My CNC build
« on: May 26, 2009, 01:45:54 PM »
THANKS MachineMaster, (I stand corrected, Arizonavideo).  YES, this wiring scheme has yielded amazing results. And I now understand your meaning about the little 1/2" acme screws turning at high RPM! (My X axis screw is 49" long). I just tried cutting a rectangular pocket 4"x7" with the feed rate set at 22 IPM. While cutting, I used the MDI screen and set the manual overide to 250% the machine just took off! However, about half way through the second pass, it lost some steps, and ruined the part before I could react. I tried jogging manually back to where it went haywire, and hit Cyclestart. That's when it REALLY lost it's mind, and went about destroying the part. I have not yet tried a different power supply- still using the 24vdc 6.3a unit. But after seeing the results of using half-coils, I am anxious to upgrade to at least a 48vdc unit. The Gecko drive supports up to 4 axis. I am currently using only 3 axis, but plan to add a horizontal/vertical rotary table with a tailstock setup as the 4th axis (once funds will permit). The heatsink I mentioned, I think will work just fine even without a cooling fan.  After running the machine for over 2 hours, the Case of the Gecko was only slightly warm to the touch, and the stepper motors felt even cooler than the drive.  There are trim adjustments on each axis of the Gecko G540- between the Motor Tuning function of Mach 3, and these trim adjustments, I am left confused as to exactly what the trim adjustments do. After swapping to the opposite end of the coil on the Y axis, I am now getting 48 IPM (according to Mach 3 Motor Tuning screen). Even after many hours of tweaking the acceleration rate, and velocity rate, this was as fast as I could set the Y axis motor to run (without stalling/losing steps). I don't understand why this is happening, since the Y axis is only carrying the load of the Z axis, and router, while the X axis is carrying the load of EVERYTHING on the Gantry (and I am getting 100 IPM on that motor).

General Mach Discussion / Re: My CNC build
« on: May 26, 2009, 08:47:52 AM »
THANKS Arizonavideo for the tip on using the center tap to reduce the mH of the coils. I am now getting 100 IPM on the X axis, and (so far) I have been able to get 24 IPM on the Y (I plan to switch the Y connection to the opposite end of the coil to see if I can get an improvement there are well). These speeds are according to the Motor Tuning function of Mach 3.  I have not yet changed the resistors, so I have no idea how much current I am feeding these motors. According to Gecko, I am supposed to use 1K resistors per desired amp of current. I currently have it wired with 2.5K resistors inline. Anyway, I tested the accuracy (looking for lost steps) by outputting gcode generated by the Write wizard, and rewound to the beginning, and repeated 5 times! The toolpath was repeated with absolute precision. Finally, after 8 months of work, I am able to get down to some "play" time! Again, THANKS for your input! I plan to eventually modify the machine design, and hope to be able to afford ballscrew drives, and linear rails for an improvement in rigidity, and accuracy (for machining purposes). But for now at least, I am able to do some nice wood carvings. Any suggestions as to WHICH surface to mount a heat sink on the Gecko G540? It is designed for surface mounting of the face plate itself, but I suspect that the heat sink will need to be mounted onto the rear surface of the unit. I have a large aluminum finned heat sink I plan to use, and mount a 12v cooling fan directly onto the ends of the (1.5" tall) fins. Now that I have the machine working with good results, I am now down to making some organization of the "Rat's Nest" of wires, and junction blocks within an old PC Case as the housing for the power supply, and driver. Again, THANKS for your help!

General Mach Discussion / Re: My CNC build
« on: May 24, 2009, 04:52:19 AM »
I am going to try your suggestion of using the center tap, and one end of each coil. Just to see.... you said this is possible, if I am willing to give away some power.  I don't think that this is going to help the situation because LACK of power seems to be the problem (Insufficient torque).  But one thing I have learned, that trial and error sometimes yields desired results. I will try your suggestion, and alternate coil end connections until I (hopefully) achieve improved performance.  Gecko recommends motors with a 2.5 to 3.0 mH coils. I researched this, and according to Oriental Motors, the PK296-01AA motors have 26 mH when wired Bipolar serial. So (if I comprehend correctly) what you are saying, by using the center taps and one end of each coil, I should realize a REDUCTION in mH of inductance (which SHOULD bring these motors closer to the Gecko recommended inductance ratings)?

General Mach Discussion / Re: My CNC build
« on: May 24, 2009, 03:56:47 AM »
Could you elaborate? "Center tap and one end of each coil" is not possible with six motor wires and only four Gecko connections. Oriental motors instructs that the center tap is not used for Bipolar serial connection of the motors. (And since they are six wire motors, parallel connection is not possible). I am confused about the center tap. Is this in essence energizing only HALF the coil?

General Mach Discussion / Re: My CNC build
« on: May 23, 2009, 04:15:18 PM »
I have since purchased a Gecko G540 driver board which supports up to 3.5a and 50vdc.  This driver did produce an improvement in performance using the 24vdc 6.3a power supply.  (But is STILL stalling/losing steps at times).  I am considering a higher voltage power supply, to use with the VEXTA PK296-01AA motors. I looked at the KL23H276-28-4B motors you recommended at Keling, but they are NEMA 23 motors, and my machine is built using NEMA 34 motors. I have read on this forum that 1200 oz in motors present performance problems, so I am considering the 960 oz in motors instead. However, having made the investment in the new Gecko drive (over $300) I am limited to 3.5a 50v motors.  Can you recommend a power supply/NEMA 34 motor combination which will work well with the Gecko G540 driver?

General Mach Discussion / Re: My CNC build
« on: March 09, 2009, 11:46:25 AM »
I have not weighed the Gantry assembly of my system which includes on it the Y axis drive, as well as the Z axis drive systems, but I estimate it to weigh around 180 lbs. Obviously, the main axis I am having problems with, is the X axis. (Since it carries the load of EVERYTHING else!). I am using ACME lead screws 1/2" diameter 10 TPI with Lovejoy motor couplings on the X and Y axis, and a .375" diameter 5TPI ballscrew on the Z axis. (This was a pre-assembled purchase which included a NEMA 23 stepper motor from ebay). All 3 axis are wired Bi-polar series. The spindle I am using is a Porter Cable 690LR which I mounted on the Z using two 2" thick x8"x8" blocks of 6061-T6 aluminum which I bored the required 3.4" hole on my southbend lathe in order to clamp the PC Router onto the Z axis slide plate. Following problems with the Z losing steps, I eliminated the top clamp block to reduce weight. The Gantry assembly is constructed of 2"x2"x3/16" angle steel (see the MYCNC.PDF file posted at the beginning of this thread).  I Guess that it is just NOT possible with the motors/driver/power supply system that I am currently using, as I said before. I have spent many frustrating hours trying different step rates, velocities, and acceleration rates trying to find a satisfactory "sweet spot" in which the motors could drive the machine without losing steps. It appears that I will have to wait until funds are available to invest in higher torque motors and drive system. Also, I have noticed that temperature seems to play a major role in the problems I am experiencing. When it is below freezing in my shop, is when the greatest failure rates occur. Now that the weather has warmed up, it seems to have improved somewhat. But the lost steps still continue. I have successfully managed to carve out my name in a block of plywood, and rewound the Gcode (which I wrote by hand for the first test, after mapping the lines which form the letters of my name on a piece of graph paper, and assigning x, and y coordinates- think BASIC geometry and writing a text file from this map to import into Mach3). The repeatability was perfect! But that was at a time when everything seemed to be functioning perfectly (it was a warm day at the time). Sorry for the long post, but just wanted to give as much relavent info as I could. Thanks for your help!

General Mach Discussion / Re: My CNC build
« on: March 09, 2009, 06:17:17 AM »
Fernado and Tweakie,
The power supply I am using is a 24vdc 6.3a switched system. I know very little about electronics, but received this one along with the Mechatronics 4 axis board as an ebay purchase. The motors were purchased from a different ebay vendor, and the specifications for them I obtained from oriental motors.com 24 volt DC 2amp per phase Bi-polar with 2ohm coils. They are six wire motors, and the wiring diagram (also from Oriental Motors) showed that for Bi-polar funtion to wire one coil to the A+ and A- and the other coil to the B+ and B- outputs of the driver board. (The center taps are NOT to be connected for serial Bi-Polar function) which is the way I wired these motors. I cannot use a power supply higher than 24vdc, as this is the limit that the Mechatronics driver board can handle. Can anyone recommend an economical solution here? The motors are rated at 420 oz in in Bi-polar mode, and I have learned that Oriental Motor offers other models which are rated as high as 1200 oz in. However they required higher amps (which the Mechatronics board can't handle) and have a $308 EACH price tag. This is more than I can afford right now. Any help would be appreciated. And THANKS for the response!

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