New Machine Build- CNC Machine advice

[jon_cnc]

I'm thinking about building my first CNC machine (a small one, about 3ftx3ftx1ft, for home/hobby woodworking use) and I think I understand how the system works. I plan for the machine to be a moving gantry using a Ryobi laminate trimmer as the cutting tool. The gantry is moved by two steppers (one for each x-axis), one for the y-, and one for the z-, with each motor attached to a 1/2-10 acme screw. I still have a few questions related to some aspects of the build, however. They are:

1. I plan to drive the machine using an arduino uno and 4 easydriver stepper motor drives (both from sparkfun.com).
- Can the arduino be programmed to treat two boards identically to drive the x-axis steppers the same way? If so, is this a programming thing or a wiring one?

2. I'm thinking about using the STP-MTR-23079 stepper motor from automation direct (STP-MTR-23079 Products). This stepper is way more powerful than what the easydriver can handle.
- Is this motor overkill or is it not strong enough?
- Will this motor (or steppers in general) be damaged by the undervoltage and undercurrent supplied by the easydriver or will performance decreases be unbearable?
- Can the easydriver outputs be connected to transistors so that a proper voltage supply can be connected to the 4 lead wires and not through the driver itself?

3. I selected a 32vdc 10A power supply (http://probotix.com/manuals/LPSK-3210.pdf) to power all of the motors.
- Can this be connected to each board/transistor (see #2 above) in parallel so that the currents added up will be around the supply's rated current?

4. For software, I am a little unsure. I don't really have the budget for an expensive program like Mach3, so I thought I could use some opensource G-code generator and Arduino g-code interpreter.
- Is PyCam paired with the RepRap arduino g-code interpreter (Arduino GCode Interpreter - RepRapWiki) a good idea?

Thanks in advance for you help!

[doorknob]

Originally Posted by jon_cnc 1. I plan to drive the machine using an arduino uno and 4 easydriver stepper motor drives (both from sparkfun.com). - Can the arduino be programmed to treat two boards identically to drive the x-axis steppers the same way? If so, is this a programming thing or a wiring one?

The easiest way to do that would be to drive both X-axis easydriver boards from the same arduino output port pin (by wiring both of the driver inputs to the same pin). You should be able to do that without overloading the port pin. If you wanted to, you could drive them from separate port pins, which would require programming to accomplish, however I don't see any real advantage to doing that.

Some people may advise driving two identical stepper motors in parallel from the same driver. I'm not certain whether or not the easydriver board's ratings will permit that, though.

[doorknob]

Originally Posted by jon_cnc 3. I selected a 32vdc 10A power supply (http://probotix.com/manuals/LPSK-3210.pdf) to power all of the motors. - Can this be connected to each board/transistor (see #2 above) in parallel so that the currents added up will be around the supply's rated current?

That is normally the way that CNC router stepper motors are connected to the motor power supply. In practice, not all of the motors are driven simultaneously at full current, so it may be possible to get away with a power supply with a maximum current rating a bit lower than the sum of all motor currents.

I would note, however, that each of the easydriver boards derives its on-board logic power supply from the motor power supply voltage, and I believe that a 32-volt supply exceeds the max input voltage rating of the board by a couple of volts.

[mmcp42]

I'm using Arduino and EasyDrivers
you can feed the logic power without having to use the motor power as I recall

If you need software I have a PC based CNCdriver that squirts gcode at the arduino and a sketch that implements gcode...

[dkirtley]

doorknob:

The current version (v4.2) doesn't supply logic off the motor current. I don't know about the older ones. I was playing with mine on a little lathe and running the steppers with 12V and the logic with 5V.

mmcp-42:

Which g-code interpreter you using? I am planning to run one with an Arduino Mega so I can play with my little LCD and other stuff as well.

[doorknob]

Originally Posted by dkirtley doorknob: The current version (v4.2) doesn't supply logic off the motor current. I don't know about the older ones. I was playing with mine on a little lathe and running the steppers with 12V and the logic with 5V.

The schematic for version 4.3 is shown at http://www.sparkfun.com/datasheets/R...Driver_v43.pdf

That schematic shows power input to the board at JP1. Coming off of JP1 (pin 2) is V+, which is the motor supply voltage. Also coming off of JP1 pin 2 is the input to voltage regulator IC2. The output of IC2 is Vcc, which is the power supplied to the logic.

There is a normally-shorted on-board jumper, SJ1, between the output of IC2 and the point from where Vcc is taken off for the rest of the board. The legend for SJ1 states, "Cut to use your own Vcc source from JP4".

So, according to the schematic, if you wish to supply Vcc independently of V+, you must cut the SJ1 trace on the circuit board, ignoring IC2 and bringing Vcc in from a separate source (pin 1 of JP4).

It is possible, however, that the SparkFun board layout does not follow the schematic exactly.

[mmcp42]

Originally Posted by dkirtley ... mmcp-42: Which g-code interpreter you using? I am planning to run one with an Arduino Mega so I can play with my little LCD and other stuff as well.

I wrote it myself (ok I ripped off various code-fragments and use lots of sticky tape!)
The combination of CNCdriver (in the PC) and Arduino sketch seems to work ok
No reason why it shouldn't work on a Mega

If you're interested I'll post links to the two pieces of code

It is aimed at PCB milling so the PC on-screen "virtual mill" is 2D
You will need to configure the sketch to fit
a) your stepper "steps per inch"
b) what is connected to which pin

It does support:
a) 3 steppers
b) limit switches on all 3 axes
c) reasonable subset of gcode

let me know

[dkirtley]

Cool, I had not even noticed that.

When I got in this morning and looked, since you got my curiosity up. The trace is connected. I don't really know if it makes that much difference then in the long run. I just followed the wiring diagram and sample sketch from the board designer and it just worked, so I didn't spend a lot of time looking into it.

Originally Posted by doorknob The schematic for version 4.3 is shown at http://www.sparkfun.com/datasheets/R...Driver_v43.pdf That schematic shows power input to the board at JP1. Coming off of JP1 (pin 2) is V+, which is the motor supply voltage. Also coming off of JP1 pin 2 is the input to voltage regulator IC2. The output of IC2 is Vcc, which is the power supplied to the logic. There is a normally-shorted on-board jumper, SJ1, between the output of IC2 and the point from where Vcc is taken off for the rest of the board. The legend for SJ1 states, "Cut to use your own Vcc source from JP4". So, according to the schematic, if you wish to supply Vcc independently of V+, you must cut the SJ1 trace on the circuit board, ignoring IC2 and bringing Vcc in from a separate source (pin 1 of JP4). It is possible, however, that the SparkFun board layout does not follow the schematic exactly.

[dkirtley]

I would love to look at it. Always like to look at interesting code. I plan on making a small scale Arduino based machine as well as my big one for a test bed. I had seen the one that they have from the RepRap project that someone here was using for a cutting machine but they seem to have just posted it at disappeared.

I have been thinking about getting an flash memory reader so I could spool a job but I really don't know if it would be the best of ideas. Long cutting jobs without feedback could be problematic.

Originally Posted by mmcp42 I wrote it myself (ok I ripped off various code-fragments and use lots of sticky tape!) The combination of CNCdriver (in the PC) and Arduino sketch seems to work ok No reason why it shouldn't work on a Mega If you're interested I'll post links to the two pieces of code It is aimed at PCB milling so the PC on-screen "virtual mill" is 2D You will need to configure the sketch to fit a) your stepper "steps per inch" b) what is connected to which pin It does support: a) 3 steppers b) limit switches on all 3 axes c) reasonable subset of gcode let me know

[mmcp42]

sorry
missed your reply

you can find the code here:
this bit (CNC driver) sits in the PC and spits gcode at
this bit (Arduino interpreter) that runs in the Arduino

you will need to configure it (_init.pde)

enjoy

btw if you make any changes do let me know so I can keep in step (<- you see what I did there!)

[dkirtley]

I finally found this thread again. Lucky that I recognized your avatar pic

Originally Posted by mmcp42 sorry missed your reply you can find the code here: this bit (CNC driver) sits in the PC and spits gcode at this bit (Arduino interpreter) that runs in the Arduino you will need to configure it (_init.pde) enjoy btw if you make any changes do let me know so I can keep in step (<- you see what I did there!)