stepper motor driver for small CNC

[student1616]

hello all,
iam building a small CNC machine for my personal use.
using steppers from old printers and scanners (they have some 6 and 5 wire).

i was following 3-axis driver details from electronic-lab (https://www.electronics-lab.com/projects/pc/008/index.html)
it uses ULN5804 chip.every thing was ok until i inquired abt the cost of that chip.its costing a lot.i can' spent so much on one chip.
so does any one have idea for a good driver chip with ckt details.which is available in market.

pls help me.
thanks.

 

[HiTech]

There is a stepper motor driver in the STK series (I don't remember which one) and it's capable of driving a sizable motor. However depending what this CNC machine is to do for you, printer motors are low torque. I hope you aren't trying to build a small milling machine using those motors. You can also buy a stepper motor control circuit in kit form from many of the kit supply outfits on the Internet. They are cheap to buy.

 

[phalanx]

Allegro Microsystems makes driver IC's with varying capabilities. **broken link removed**

I've used their A3984 driver extensively with great results.

 

[student1616]

well its a very small one.
the machine is capable of milling/drilling/engrave a small plastic or wood piece.
i want to built one for 3 axis in one circuit.
A3984 driver ! i'll try this.but as these circuits shld be made with good sloder.do u have any pcb layout? so it will be quite easy to make.
i hope u don't mind.
and thanks for ur replies guys.

 

[Mike - K8LH]

Allegro Microsystems makes driver IC's with varying capabilities. **broken link removed**

I've used their A3984 driver extensively with great results.

Forgive me if I'm going "off topic" but may I ask if you have an example you could share (I'm interested in that chip)? Thanks. Mike

 

[phalanx]

When I get home I can see what I have to show. Most of my applications were for commercial purposes so I can't post all the details of the layout. I do have a board that I made for hobby purposes though. It is far from an ideal layout but it worked the first time so I never changed it.

There is a thread in the robotics forum that deals with a different Allegro driver IC. There are even schematics posted. https://www.electro-tech-online.com/threads/allegro-a3977-idle-noise-help.23416/

The Allegros are very easy to use and there are examples available from their website. All you really have to do is connect your external caps, sense resistors, and reference voltage to the chip (explained in the datasheet) and then tie the control lines to PIC pins and you have yourself a working motor controller. The hardest part of my design was taking into account the thermal pad in the TSSOP parts while laying out the PCB.

My biggest project was a precision 3D stage with absolute position feedback for telescope optics and sensors. The stage had a 7cm range with 100 nanometer resolution in each axis (and it had to operate at 70 degrees Kelvin in a high vacuum). Since I had to control 3 motors, the A3980 significantly reduced the processor overhead needed to control them and it made the drive circuitry much smaller. Not having to worry about PWM generation for 3 motors allowed me to concentrate on the signal processing to get accurate data from the capacitive position sensors used for absolute position feedback.

 

[student1616]

thanks for the info.
its very detail.
it seems that Allegros chip can handle some real operations.
mine is a first prototype made from cardboard material (once it worked then i'll built some real machine)
my friend said L297+l293 or L297+L298 combo. is cheap and will serve my purpose.
does any one used these chips before? some circuitry of these will be appreciated.
thanks once again

 

[fever]

i found a simple 3-axis driver based on ULN2803.its a pretty old one and will work.
**broken link removed**
**broken link removed**
scroll down for the circuit.

but i wonder how efficient it is.
and how safe it is?
and the connections are also not so clear in the layout.imean where to connect power supply,limit switches etc.and what are those 1 2 3 M at the top.
can some one clarify these

 

[student1616]

has any one tried this before.
and this doesn't look like 3 axis.one for -X and other for -Y and 3rd one for emergency i think.
if some one has proper layout and details pls do post.
thanks

 

[hjames]

I assume you've already looked at links like:
https://www.linuxcnc.org/
https://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?EMC2_Supported_Hardware

This is one version of stepper driver that it supports:
**broken link removed**

Or for chuckles:
https://emergent.unpythonic.net/projects/01142347802

Personally I've outfitted my Sherline mill with a Allegro 3977 based driver, and am in the process of redoing the PCB to add optocouplers. (If only I could just finish routing the power traces instead of posting stuff...)

 

[student1616]

thanks for ur effort guys.at last i decided to built this as the parts and layout seems to be easily available.
**broken link removed**
**broken link removed**

but i have some doubts to clarify.

1.in the pic attached below is the limit switch connections are right.and what is the purpose of D2 and D5
**broken link removed**

2.and i have 5 wire stepper motors(that makes them UNIpolar).so while connecting them i have to connect the common one to ground and remaining 4 wires to respective terminals. is it right?

i'll be waiting for ur reply.
thanks once again.

 

[hjames]

"D2" and "D5" are just the names of the pins on the parallel port.

And yeah the common connection on the stepper goes to VCC. Keep the voltage below the motor's rating. You might want to read up on "L/R drives, ballast resistor", or build the chopper circuit to increase performance.

 

[student1616]

thanks.
i have seen this power resistor for stepper motor before in an article.
it says that they are required to control the current for stepper motors.
so for a 5 wire unipolar motor,the Vcc to the common(as u said above) will be connected in series with the resistor.then how can i calculate the resistance.

another issue here is the motors i have,are taken from printers.so there is no info of voltage and current on the motors.
so is there any way to solve this problem.

 

[hjames]

Turn the printer on and measure it, or try to reverse engineer the circuit... Other than that, there's no guaranteed way.

 

[chiba]

If you ever need some ideas on building a CNC machine then have a look around this forum https://www.cnczone.com/forums/index.php?
They cover just about everything that's related to DIY CNC machines and some of the members machines are just awesome, you will spend days there.

 

[fever]

nice pcb.is it made by press and peel or toner transfer?

 

[Sceadwian]

Press and peel is toner transfer.

 

[HarveyH42]

Press and peel is toner transfer.

Not really. Press and Peel is a brand name, they made rub-on decals for many years before photocopiers or laser printers. Had them in high school (mid 70s).

 

[Sceadwian]

Yeah, but the press-n-peel blue stuff used for makeing PCB IS the toner transfer method, they just use their own special blue sheets for it. It's like a buck per sheet and one time only use. Too expensive if you ask me. I still would like to find out if you could use thin teflon sheeting instead of paper, that would be reuseable.

The decals are okay for small designs but I don't think you could get something as neat and nice as the board shown in this post using decals unless you had some serious OCD issues, at the very least you wouldn't be able to do fills like the board shows, so it has to be a toner transfer method of some kind. Or real photo resist.

 

[Mike - K8LH]

Isn't that a photo' of a routed board?