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Re: My CNC build
« Reply #10 on: May 23, 2009, 09:45:08 PM »
You could try using the center tap and one end of each coil to gain some speed.
Re: My CNC build
« Reply #11 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?
Re: My CNC build
« Reply #12 on: May 24, 2009, 04:15:09 AM »
You will never have a fast machine with steppers and a 10TPI lead screw.

I am running   5 TPI lead screw's and a 60V supply and low inductance 400 OZ NEMA 34 steppers and I can get well over 1,000 RPM, but if you watch the  little 1/2" lead screws  go 1200 RPM you know that this is not a vary good idea for a 34" long screw.


Go to a 50 V supply first, it goes with your stepper driver.

I would think with your current 420 OZ steppers at 1.2A that they will start to loose power at about 125 RPM. 50V will make that 250 RPM. Your max speed should be around 12 IPM.

Faster steppers will help but you might want to think first if you ever will want to cut at 80 IPM or so. To do that you will need faster screws.

As for new steppers you might look at the KL34H280=45-8A 640 OZ stepper or the KL34H280-45-4A

The 4A runs at 4.5A so you will have to give away about 25% of 640 OZ of torque but it has a little higher voltage that will let you run it in parallel to get better speed. The inductance is 6.8mH. I would think you could get 750 RPM.

The KL34H280-45-8A is a 8 wire motor and for a series hookup will give you a 8.8mH of inductance at 3.1A. You will get the full 640 OZ of torque but gain two mH of inductance so you will lose some speed.  The 8A would work nice with some faster screws like the 4 TPI ACMI or even the faster 2 TPI.

You current steppers should perform fine If you go to a faster screw. With 250 RPM from the stepper and a 2 TPI screw you would have around 125 IPM cutting speed. You have a lathe so turning the screws should be no problem.



Re: My CNC build
« Reply #13 on: May 24, 2009, 04:22:29 AM »
You will never have a fast machine with steppers and a 10TPI lead screw.

I am running   5 TPI lead screw's and a 60V supply and low inductance 400 OZ NEMA 34 steppers and I can get well over 1,000 RPM, but if you watch the  little 1/2" lead screws  go 1200 RPM you know that this is not a vary good idea for a 34" long screw.


Go to a 50 V supply first, it goes with your stepper driver.

I would think with your current 420 OZ steppers at 1.2A that they will start to loose power at about 125 RPM. 50V will make that 250 RPM. Your max speed should be around 12 IPM.

Faster steppers will help but you might want to think first if you ever will want to cut at 80 IPM or so. To do that you will need faster screws.

As for new steppers you might look at the KL34H280=45-8A 640 OZ stepper or the KL34H280-45-4A

The 4A runs at 4.5A so you will have to give away about 25% of 640 OZ of torque but it has a little higher voltage that will let you run it in parallel to get better speed. The inductance is 6.8mH. I would think you could get 750 RPM.

The KL34H280-45-8A is a 8 wire motor and for a series hookup will give you a 8.8mH of inductance at 3.1A. You will get the full 640 OZ of torque but gain two mH of inductance so you will lose some speed.  The 8A would work nice with some faster screws like the 4 TPI ACMI or even the faster 2 TPI.

You current steppers should perform fine If you go to a faster screw. With 250 RPM from the stepper and a 2 TPI screw you would have around 125 IPM cutting speed. You have a lathe so turning the screws should be no problem.




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?

By center tapping you will lose half your torque but double your speed(more than double). The current will be the same but you might be able to bump it up some and still have the motor stay cool. You will have a lot more power at 250 to 500 RPM. With a 10 TPI screw I would think 200 OZ might be OK but you will need to find out by testing.

They say not to use the center tap for bipolar but you can if you are willing to give away some power.

To center tap means to use the center tap and only one of the other two wires.
« Last Edit: May 24, 2009, 04:27:05 AM by arizonavideo »
Re: My CNC build
« Reply #14 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)?
Re: My CNC build
« Reply #15 on: May 24, 2009, 12:35:14 PM »
In the electronics world inductors are called "chokes". They are often used to stop high frequency's from passing through a circuit. For steppers with slow screws we don't want high inductance. You motors have a vary high inductance and voltage rating. This will allow them to  work with a low current driver like the Mectronics but the price is speed.

28mH is a huge value. Your inductance if you use a single coil should be around 7mH so the speed will be close to what the the 45-8A stepper would give.

A 50V supply and a 7mH coil should give you over 500 RPM and still hold 200 inch of torque. You might be able to get 50 IPM before the torque starts to fall off with that setup.

Your motors would be happier with a 100V supply or a unipolar driver or faster screws.  In the long run I would look at getting the much faster screws. They are more efficient and will let you use your existing motors just fine.

You might take a look at the Roton #60986 lead screws, 4 start and 2 TPI with the dumpster nuts.

You want to use the lathe anyhow!
« Last Edit: May 24, 2009, 05:19:29 PM by arizonavideo »
Re: My CNC build
« Reply #16 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!
Re: My CNC build
« Reply #17 on: May 26, 2009, 11:12:05 AM »
If you use heat sink paste and remove any coating from the PC case where you mount the Gecko, you can mount the Gecko inside and the heat sink on the outside.
Re: My CNC build
« Reply #18 on: May 26, 2009, 01:12:27 PM »
It was not my idea to only use one half of the two coil but MachineMaster. I have not tried the idea myself but it should help and the price is right.

I think the Gecko current drive resistor is the same as the current made, so a 2.2k= 2.2A which should be over driving the steppers some.

I have over driven some steppers and they did not improve the power much and got really hot. I have not read anything about coil saturation effect on steppers so I don't know what gains might be had by overdriving a single coil. The motor will run cooler with a single coil being used so heat should not be a problem. If you can run 2.4A and the performance is fine and they don't get too hot you might be OK just leaving them set that way.

Did you up the voltage?

The little Geckos don't need much heatsinking and at 2.2A almost any heatsink will cool them enough. A slice of 5" x 1 1/2 AL angle stock should work fine and bolt it to the box. You could go all out and get a 10" piece. ;D
Re: My CNC build
« Reply #19 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).