Re: [CAD_CAM_EDM_DRO] retrofitting an older CNC

no falloff <nofalloff@...> wrote:

After using CNC mills both at a friends shop, and as school, I decided I just had to have a machine of my own. After saving for the better part of a year, I just bought a CNC Shizuoka mill with a Dynapath Delta 20 controller (pics at: www.cyclegarage.net/mill). I�m not sure if the controller is any good. It seems to work but I�m getting a fault on the Z axis. I bought the machine figuring that the controler wasn�t working, and had planed to replace it (of course only knowing enough to be a danger to myself and others :-) ). It seems retrofit controller systems by Centroid, and Anilam etc. are way too expensive for my current budget. I was hoping to use as much of the existing hardware (servos, servo amps and electronics) as possible, and just use a PC as the controller. The mill is currently fitted with Baldor permanent magnet servos. The book for the servo drives (the only documentation I have) mentions that the drives are looking for PWM signals from the controller. I know that
one could probably write a book in response to my questions, but I just need a general bit of clarification.

Get a Dell 2.2 Celeron for $349 delivered. Install Mach2 $150 on it (runs very smooth) Use Gecko 320's for your drives $114 a piece. Bob Campbells PC to Route breakout board $130 or so. I just retrofitted my Bridgeport from an old Bandit stepper system. I used Allen Bradley Servos and I use this machine everyday and dont have one complaint with it. To date it has not lost a single step to my knowledge nor has it made any unexpected movements on its own. Mach2 is a very easy and reliable program with alot of features. The nice thing about it, It's user adaptable. If you want to do simple tasks you dont have to be a PC whiz to perform work with it. It has alot of advanced features but, If you dont want to deal with them you dont have to. I have some pics of the enclosure and the control interface that I built. If you are interested let me know.

1. Systems that use gecko drives don�t have absolute feed back? That is, the computer sends motion signals (step and direction) to the drive but has no way of knowing if the servo is in the position it is supposed to be in? How does this compare to the positional accuracy as compared to the current system?


Yes the G320 servo drive uses feed back. Through an encoder. The best thing to do is just replace the existing ones. US digital has an E5S-200 with the proper Ma draw suited to the Geckos for about $40 a piece. The reason I favor the 200 line quadrature is: with my 2.5:1 reduction on each axis every step equals .0001 of an inch exactly. So 10,000 steps per inch and Z is 20,000 steps per inch. The accuracy with mine is daunting. .0001 resolution, checked it with an indicator it is there. Not just numbers on a screen. One good reason to replace the encoders is for safety's sake. If you lose an encoder on a DC servo system the axis will run away and only stop when it crashes or hits the limit switch. always be aware of this.


2. Does the fact that mach 1 uses step and direction commands mean that it can�t be used with the existing servo boards in this machine? If not what controller software (EMC?) would work?


It isnt worth toiling with. Throw the old junk out.


3. How do I interface it with the existing hardware? If the servo amps don�t except step and direction signals, then I assume that a simple breakout board such as those used with gecko systems won�t work. Likewise anyone have suggestions as to what will?



4. These servos are rated a 120v and 10A (continuous) 39A (peak). It is my understanding that these can be used with gecko 320 drives, but will not achieve their maximum rated torque or reach their 2500RPM max rated speed. Is this correct? Will the tachometer need to be replaced with encoders in order work with this system? Rutex drives seem a better choice, true?

The Geckos work perfectly on my Bridgeport. No heating problems..nothing. And I'm driving the knee with a 40 in/lb. motor. I ran a profile program that was 2 hours long (30,000 lines of g-code) and the Z was whipping up and down the whole while. I did it to test it. The motor got a little warm but the Gecko on a heat sink with a fan was hardly warm at all.



They must be DC brush-style motors

I'm using 100 volt servos, 13.7 amps continuous and 26 amps peak. As long as you supply the necesary amperage you will not lose any torque. the Geckos are rated at 80volts and 20 amps. My transformer is putting out measuring from the bridge rectifier about 68 volts DC. Measuring off the transformer it is less due to the RMS. But you will lose some speed and on a vertical mill. who cares? 2500 is way too fast even for a 3:1 reduction. the voltage from your existing power supply will be too high for the Gecko's, So the output will need to be changed or change power supply's. www.cnckits.com has them for about $400 dollars completely wired and ready to go. $h*tcan the tachometers, you dont need them. One important thing to remember: Use two pair sheilded cable and run A and B channel from the encoder in separate pairs and keep the encoder cable as far away from the motor leads as possible. They will crosstalk and give you fits if you don't. This means two separate plugs on the servo
motors and the control enclosure.


Lastly. How hard would it be to include the stepper motor controlled spindle speed, and tach into the new controller? Could this be done by defining it as say a 4th axis?

As I undertstand it. Bob Campbell who makes the Breakout boards is making an auxillary board that plugs into the breakout board for spindle speed. I'd like to have that myself. Or you could always incorporate a small DC servo and run it as a 4th axis. But the programming would be more difficult. I'd just wait for Bob's board.

I�ve been searching and reading as much as I can, and have royally succeeded in confusing myself. Any links and information I get I plan on including on a page on my web site covering everything I do to get this machine running. I hope to document everything I go through, as other who have done so are what inspired me to try this crazy stunt. >:-)

The most difficult portion of your retrofit is going to be the Power supply. Many on the board here can help you with that. They did with mine and all of the info I received was right on the money. The rest of the components are "plug and play" practically.



Thanks in advance for your help.



Peter-

pdh@...

(remove knowspam to reply)





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