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Re: My CNC build
« Reply #20 on: May 26, 2009, 09:09:28 PM »
I can get 300 IPM with the 400Oz steppers and 60V and 5TPI but I will lose steps if you let it run long enough. I have only just started cutting parts but I have slowed things down to 150 IPM for rapids and have not lost any steps.

The 48V supply will give you a 50% speed increase so it is worth doing. To make sure you don't drop stepps you will need to slow thing down more than you think. I would be happy if you got a good strong 60 IPM cutting.

I am still curious about how a single coil behaves with lower or higher current. Can you use twice the current and still get 400OZ out of it? Your motor was a 1.2A for a series connection? Correct. If you run it at 2.4A then you still should make close to 400OZ of torque. Does this happen?

The adjustment on the Gecko drive is to get ride of the inductive ring from the motor. It should happen around 900PPS.  Set the motor to 900 PPS and adjust the pot until the motor makes the lowest amount of noise. You will only need to do this once.
Re: My CNC build
« Reply #21 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.
Re: My CNC build
« Reply #22 on: May 27, 2009, 09:12:18 PM »
I'm fairly new to a lot of this stuff so I'm not sure if you should wait for instructions but I will give my 2 cents worth.

When driving a stepper, Current = low speed torque. Voltage =  speed.

For your steppers any power made past about 1000 PPS and higher is determined by the voltage. The current could be set 20A and the motor would make no more power.

Below around 900PPS the power and current is set by the driver.

If you are loosing steps at a low speed then you need more power from the steppers or driver. If you are losing steps over about 1000 PPS then the power supply voltage will help.

It sounds like all will be fine when you go to a 48V supply. The drive will die with a 67V input so you can't over volt much.


The motor tuning is described in the Gecko instructions but I think they use the term low speed and don't give a exact PPS # because it is different for every type of motor.

In Mach3 I have been tuning the motors using the servo motor function. Go to Diagnostics tab then click the Servo Freq Gen button. You can set any PPS rate from there. There is no ramp up or slow down when changing direction so you will lose steps at higher frequencies using this function.

Enter a # of PPS in the Hz box, some will be much louder than others. Try 700 to 1500 in 100PPS steps and you will be able to hear the "ring" Leave the setting there and adjust the Gecko trim pot so the motors makes the least amount of noise.
Re: My CNC build
« Reply #23 on: June 24, 2009, 08:22:19 AM »
Arizona,
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!
Re: My CNC build
« Reply #24 on: June 24, 2009, 02:35:12 PM »
You still might try hooking up the steppers in parallel.

You will only make around 500 OZ of torque but your top speed will be more than double. I would think of 150IPS rapids and cutting at 80 or 100IPS.

With less torque the motor tunning will need to be changed to allow more time for the motor to change direction. There is always a price to pay, faster cutting, faster rapids but slower change of direction.

Glad things worked out.
Re: My CNC build
« Reply #25 on: June 27, 2009, 09:42:18 AM »
Arizona,
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.
Re: My CNC build
« Reply #26 on: June 27, 2009, 01:59:25 PM »
First, no fuse!

If the fuse were to blow the back EMF wave from the motor might kill the drive. Dont use a fuse. They say this in the instructions.

The driver will never make more than 3.5A. It would be nice if you could get 4A from them somehow but you just cant. Set the resistor to 3.5A and you are done.

Most steppers are wired in parallel. You will gain top end speed but loose about 30 to 40% of your low speed power. If you are cutting soft material then you may want speed more than just 12 IPM power.

You did not say if your dropping steps all the time and if it is at high speed or low speed.

With an parallel connection you will have more power above about 800 PPS or 400 RPM than you do now but almost half the power at 200 PPS. There is no danger to this hookup, the only question is if it is a better way or not for your use.

Do you need to cut at 80 or 100 IPM?
Re: My CNC build
« Reply #27 on: June 28, 2009, 03:50:41 AM »
Arizona,
YES - I would like to cut wood at 100 IPM! Wired serial, I am only able to tune the motors to about 76 IPM (without losing steps- by "losing steps" I mean the motors whine without turning if I try to tune them above about Velocity of 76 IPM and Accelaration at about 18 IPS). I will try the parallel scheme tomorrow, and report back with the results.
Re: My CNC build
« Reply #28 on: September 07, 2009, 01:32:45 AM »
Hi, I am a beginer, i want to make cnc hot wire cutter, what should we do, what sould we buy. Tq
Re: My CNC build
« Reply #29 on: September 07, 2009, 05:01:15 AM »
I am not familiar with Hot Wire Cutters, and cannot offer any information regarding the wiring for such a tool. However, as I comprehend it, CNC can be used to drive your "tool of choice". Mine happens to be a Porter Cable LN690 wood router. Please see the MYCNC.PDF file (attached at the beginning of this post thread) for a drawing of the table design I built to drive the router (tool of choice). Perhaps others on this forum could help you with the wiring of the tool itself. But as far as what I have actually built, the PDF lists most of the components. I am using an old Dell Optiplex computer with 2 GB of memory & Mach3 software. For the driver I have a Gecko G540 driver board. And I upgraded the stepper motors to 900 oz/in from Keling Technologies. I am using 1/2" diameter 10 threads per inch ACME lead screws to drive the X and Y axis, and a 3/8" diameter 5 threads per inch ball screw to drive the Z axis on my table. Having said all of this, I am sure that it probably conflicts with some of the items I listed in the MYCNC.PDF file. The items listed in the file were acurate at the time I wrote the file. However, I have since "upgraded" to the items listed here, because the used motors, and driver board, and power supply I originally started with were a source of major frustrations trying to learn how to use the Mach3 software with unreliable components which would not function consistently. After upgrading to the components listed above, I have created many beautiful pieces on my router table. I am still evaluating various design software packages, and have so far been most impressed with Vectric's V Carve Pro. Lack of funding prevents me from any new purchases for now, but plan to later. Hope this helps to point you in the right direction to get started. I will say this, (repeating the advice of others on this forum) Buy RIGHT, Buy ONCE! If you cannot afford to buy new QUALITY components, then Don't Buy until you CAN afford to! This will save you a lot of un-necessary frustration, and money! Do as much research as you possible can, in designing your machine, and the best components needed for your use before buying anything. Unfortunately, it is the "school of hard knocks" that will be your best teacher in all of this. But you will learn along the way.