Imformation overload, Homebrew CNC

[thuffner3]

Imformation overload, Homebrew CNC
(Post #1 )

Ok, now that I've been throughly (much by my own doing) drown in imformation.

Ok, This is where I'm at right now. (Things are working, or at least moving in a linear fashion).

I'm using this controller,
http://www.stepper3.com/31.htm

I'm using these three motors,
http://cgi.ebay.com/ws/eBayISAPI.dl...item=2582180840

I've hooked into the +lines 1 ohm resistors(no idea what the watts are).

PSU, is standard older ATX 300 watt.

I'm running KCAM4.0. (Have noted, I should use TurboCNC).
on a Win98 system p166 -w- 32 mg ram standard laptop.

I was noticing some flatness on circles, say larger than 3" dia.
This flatness occurred on the x-axis.
(I was told this could be caused from a machine/mechanical problem).
Check system, Same type x-axis configuration as y-axis.
(would think flatness would occur in both directions if mechanical).
Check motors, x-axis motor seemed to be really light in the torgue area.
(this was while running KCAM4.0).
Tried TurboCNC, the torgue output was there for the x-axis but seemed to stutter somewhat.)

??Idea's??
I downloaded the resistor calculator. If my controller has "FETS"
my motors require 5.00 ohm /7.2 watt resistors.

If my controller has resistors. my motors require 4.25 ohm/6.12 watt resistors.

FETS and RESISTORS are alien to me. as are the watts for the motor power resistors.

Can I find the required power riesistors given the info above?
And do I have a decent setup for a homebrew system?

Thank you much in advance for any input.


Merry Christmas.
Peace
In GOD
Neil

[nervis1]

I'm not sure that this is your issue but check it out. I had the exact same problem when I built my first home brew. I used a Rong Fu 31 with servos and the flashcut boxes.

My first part had a flat on the top of a circle just like yours. It took me about 30 min to figure out the head wasn't fully tight on the column.

Could also be backlash in the y axis, either at the nut or at the pillow block (or in the software compensation).

I hope thats your problem, easy fix.

[thuffner3]

My system seemed to have trouble as it was trying to do very small steps(combined x & y axis) coming around the quadrants.
I slowed the unit down to max IPM of 10 and it's doing fine.
Thanks for the reply
Peace
Neil

[High Seas]

Neil -
You've experienced the same thing I(and I'm sure many others) have being the "systems integrator" on our homebuilt cnc. Have you tried the freebie version of MACH2? You could check and see if the ipm problem is a software hang up or hardware/controller (stepper3) challenge. Power and motor come to mind too. And its always good to check for the loose fittings etc in the mechanical set up too as nervis1 suggested.

BTW - it would be really cool if someone with heaps of experience could post an integration checklist. Something that lists what they know works really well together. For example - I see a lot of users very happy with Xylotex and Mach2 with PacSci 23 motors -- and get good rapids and ipm while milling. I've got 66percent of that and am considering Xylotex for the second system. But would love to hear of other configs too. Gives us all something to strive for without spending the little excess capital we may have.
Jim

[Urgundiz]

Originally posted by thuffner3
Imformation overload, Homebrew CNC
(Post #1 )

I downloaded the resistor calculator. If my controller has "FETS"
my motors require 5.00 ohm /7.2 watt resistors.

If my controller has resistors. my motors require 4.25 ohm/6.12 watt resistors.

FETS and RESISTORS are alien to me. as are the watts for the motor power resistors.

Can I find the required power riesistors given the info above?
And do I have a decent setup for a homebrew system?

I think you mean FETs and Transistors, not resistors. Both of them are semiconductors designed to control the flow of electrical current. FETs do that using a low voltage, and Transistors (or TRNs, is the same) use a low current. The way both of them are used in Stepper control is like a valve, full ON or full OFF creating square waves of electrical current that when enter the stepper 'makes' the steps.

The resistors needed are a way to limit the current that you push to the motor (remember, the 'valves' are full ON or OFF). Think of them as a 'pipe' that limits the flow but is not capable of cut it.

Because the different technologies that FETs and TRNs uses, the resistor is different in both cases. A resistor has two main parameters, resistance (the diameter of the pipe) and wattage (the pressure the pipe is able to resist). Resistance is a parameter that must be as close as possible to the desired, and wattage is a parameter that must be equal or higher than desired. With your calculations, you need:

In case of FETs: resistors as close as possible to 5 ohms, and 'at least' 7'2 watts, so you can use 5 ohms 10 Watts, or 5 ohms 25 Watts, for example.

In case of TRN's: 4'25 ohms and at least 6'12 watts, so you can use 4'25 ohms and 10 or 15 or 25 watts.

In order to locate the power resistors, you can go to radioshack or similar where you buy electronic components. Or ask to a TV repairer or similar person where to go in your neighborhood. Be sure to buy the closest value of resistance and a value of wattage equal or higher.

To know if you are using FETs or TRNs, from the link you have posted I've read the manual of the controller and there is no info about it, so the best way is to see the reference number in them (look at the front of the dispositives that are 4 in a row, these are the FETs or TRNs). Put that reference number in google, and the answers will say 'FET bla bla bla' or 'Transistor bla bla bla'. That's the easy way.

Hope it helps..
/U

[balsaman]

With Steppercalc, when in doubt, choose Transistors. The result won't be optimum, but it will be safe for your motors.

E

[thuffner3]

Thanks for the info Guys,
I like the way your thinking High Seas, in regards to a basic intergration break down. I think that would be so helpful. And save alot of double questions. It's so hard for a newbie to wollow through all the possiblities. Man, I'm still wollowing. But at least my machine is working. I'm loosing steps somewhere, but it is getting better.
I believe somewhere at about 2500 linear inches of travel along the x axis my machine looses about an 1/8" 0r .125", then it dramtically increases from there to about 1/4" or .25". I think this has alot to do with my settings in TurboCNC.

[High Seas]

thuffner3 --

Ya right! I was seeing about the same losses after 25000 lines of G-code. Opted to slow down the feedrate and got it right. Made me suspect the motor/power (other pointers to that too) so opted to replace the motors -- better now.
Thats why the "extra" set and a new cnc in the woiks! Maybe we should just keep good notes and publish our own mini-tome?
Jim

[trent2530]

I have 24 vdc with Gecko 201's and 7v, 1amp, 125 oz-in steppers and 5/16 by 18 lead screws. 60 ipm jog rate. Should be double that if I go to 48 vdc.