[chuckknigh]

Hi, guys. It's been a long time, and I'm *baaack!*

L298N Stepper Motor Driver Controller Board Module 5V output for Robot Smart Car | eBay

Got a question for y'all. I found a whole series of L298N based stepper driver boards on eBay, and the price is ridiculously cheap. Like $6 or $7 each, including shipping. Yep, Chinese. But at least they're not using that *other* chip. These are rated for up to 2A, and a high enough voltage (35VDC) to give some decent speeds, so they should be sufficient. And they're so cheap, that they're actually cheaper than I can buy the parts.

Since my latest project is a CNC on the insanely cheap, a true starter unit, would one of these work for driving each axis? Yes, I know they're not opto-isolated...but it's supposed to be basic. Think "one step above" the Easy-CNC unit on Instructibles.

As I said, the project is a cheap 'n dirty starter, yet real CNC, but certainly not a production machine...I just need to identify something workable that won't be 90% of my budget. 3 of these would only cost around $21, combined. For the purpose of this project, cost *does* matter.

Thoughts? Suggestions?

[HorridHenry]

I find that they're waiting for bids,starting at $0.01 and I doubt very much they will let them go for that much with free P&P.

[chuckknigh]

I find that they're waiting for bids,starting at $0.01 and I doubt very much they will let them go for that much with free P&P.

I already won one at $5.53, and buy it now is usually around $7. I'm happy to experiment, but would appreciate feedback from the community. What do you think of the board? As a basic way to make the motors move...

Here's one with a buy it now price:
http://www.ebay.com/itm/L298N-Dual-S...item2a181f8a67

And, here's the schematic:

[HorridHenry]

Pretty cheap them,I just worked the price out and works out at £4.40 UK sterling.

I have a project in mind using a small handheld driver for operating the stepper motor.
This project I would say I could knock em out at about $60 or $70(£50) providing I get the parts dirt cheap.

Alas my CNC isn't built yet and I don't want to count me chickens before they hatch but if my CNC was up and running I'd be buying about 50 units off that seller,I reckon he'd gimme some discount on that many.

[doorknob]

Just to be sure that you know what you're getting - these do not directly accept step and direction signals from software such as Mach3 or LinuxCNC. Rather, whatever is driving the board must supply the proper stepper motor phase excitation pattern to get the desired motor behavior. That pattern would typically be supplied by an L297 chip, which is not included.

[chuckknigh]

Just to be sure that you know what you're getting - these do not directly accept step and direction signals from software such as Mach3 or LinuxCNC. Rather, whatever is driving the board must supply the proper stepper motor phase excitation pattern to get the desired motor behavior. That pattern would typically be supplied by an L297 chip, which is not included.

Thank you. Most helpful. And, that's why I bought only one of these boards...experimentation.

I was thinking of wave drive, direct from the parallel port, for 2 axes. As I said, absolutely basic.

[aarggh]

Interfacing an L297 shouldn't be too hard, it is a fairly classic and very widely used design. I got some controllers off an old Bridgeport style mill and it was using these chips to control it. On the other hand, could you trust the signalling direct from the parallel port to do all the work with just an L298? I would think it would require some form of conditioning to function at a bare minimum?

cheers,
Ian

[kirk_wallace]

Sparkfun sells an L298 based board here:
Motor Driver 2A Dual L298 H-Bridge - SparkFun Electronics

There are some comments on that page that may help. I ran into one problem mentioned there, in that you need to be careful what diodes are used for the free-wheel diodes. They need to be fast, have a low forward voltage, have a high reverse voltage (2x or more than the motor supply) and be able to stand the maximum current. I recall trying 1N4000 type diodes and they didn't work well at all. I got a set of Schottky diodes and they made a big difference. To get the most from a cheap board, you may need to replace these diodes. You may also need to run the board at the maximum voltage to get enough power to do anything on even a small CNC. I seem to recall the maximum voltage on the board above was limited by a voltage regulator on the board and not the L298 driver, so you'll need to track down the max voltage for all of the components that will see the motor supply. A heat sink will be needed for decent power levels too.

I would not worry too much about the inputs not being isolated if you use a cheap PCI parallel port card, but isolation is easy to add if you are handy with a soldering iron, or isolated break-out-boards can be found pretty cheaply.

LinuxCNC (EMC2) can drive the L298 directly if you call out the proper configuration. There is a step type setting that outputs the quadrature pulses that you would need. My mill uses the same setup except the drivers drive eight amps at 45 Volts:
Conversion of Shizuoka ST-N from Bandit Stepper to EMC2

You can add an L297 to convert step/dir into quadrature pulses like here:
[ame=http://www.youtube.com/watch?v=PgG8IlkXFeQ]EMC2 CNC L297/L298 - YouTube[/ame]

I think I've seen a hex nand chip do the same thing.

The L298 datasheets have a lot of good information.
http://www.st.com/internet/com/TECHN...CD00000240.pdf

Also, if you run the driver close to the maximum current, you should consider some sort of current limiting feature. A simple current limit resistor can work but will limit performance. You'll need to get fancy if you want to drive the L298 near the limit and have a chance of it staying alive.

That's what comes to mind so far.
--
Kirk Wallace
Kirk Wallace's Machine Shop
E45 Pine Mountain Lake Airport Webcam
California, USA

[chuckknigh]

Love the enthusiasm, guys...but I don't really want to totally re-engineer this board.

I am, however, open to the idea of an interface board, like one of the cheap Chinese ones. An extra $15 or so might be a decent (and scalable) investment to recommend for a cheap intro router.

What about something like this?
CNC 5 Axis Breakout Board interface for Stepper Motor Driver Mill/Input Power:5V | eBay

Would this put out the right signals to drive the board? Can't find any based on the 297, but this seems "close." As my electronics skills are lackluster at best, and especially since I intend this project for complete newbies, I would prefer not requiring them to redesign a board they buy.

And, a separate, multi-axis breakout board could be reused for more sophisticated projects, later on.

[kirk_wallace]

The beauty of this less expensive hardware is that you get to to experiment and learn without having it it cost too much when you burn things up. The more expensive hardware lets you get something that works well without having to know all the details. The really expensive stuff gives you something that works, is easy to put together quickly, and you don't have to know anything other than how to put plugs together and flip a switch. They are all valid systems, but very different.

As for the breakout board, generally they condition the parallel port signals, so you can drive decent loads such as a small relay, LED or motor driver input, and also drive 5 Volt signals if the PC parallel port happens to be of the 3 Volt variety. Another function that is sometimes included, is isolation so that if something at high voltage happens to short out to a parallel port signal, it won't go back into your computer. Finally the break out board provides terminals that are easier for connecting wires. Many boards don't have high voltage isolation, so you will need to check the details. On the other hand, the break out board generally does not change the signals coming from the computer, only makes them a little stronger, safer and more convenient to use.

So with a break out board and L298's, you will need to figure out how to get the software to give you quadrature signals, which needs two pins per motor, one for A phase and one for B phase. If you want to add an L297 or other step/direction to quadrature converter or use a step/direction drive, then you will still need two pins per motor, and also tell the software to give you step and direction signals.

If you want to leave your L298 boards as they are, you will need to be very careful about the making sure the motor isn't allowed to pull current above the maximum. Which means buying a motor with higher impedance windings, or keeping the motor supply voltage low, or adding current limit resistors somewhere, or run the risk of blowing out the driver at any moment and often. And the performance may be very disappointing. The boards are cheap enough that you can wire up one motor to see what happens, then decide if it will do what you want.

If you don't want to get into these details, there is nothing wrong with that, but if you want something that works, you'll need to pay someone else to take care of the details in their more expensive products. Hopefully you can find a complete working system in the required price range. It could get you to machining parts faster than trying to build the machine yourself.

Just my two cents worth.
----
Oops, I reread your original post. So for "...would one of these work for driving each axis?" In my opinion yes with a big but, only a Tom Thumb sized machine, or not very fast, or not without knowing enough (a lot) to get every bit of performance out of it. I think these things are really better for small, low voltage, battery powered robots.

Again, just my opinion from working with this driver chip. It certainly would be interesting if you give it a try, and prove me wrong.
--
Kirk Wallace
Kirk Wallace's Machine Shop
E45 Pine Mountain Lake Airport Webcam
California, USA

[doorknob]

Unfortunately, the output of that board is not what you need - it provides a step and direction signal per axis, which could be used as the input to an L297, but not as the input to the L298 (unless you were to create your own software driver).

[doorknob]

I took a closer look at the alternate EMC2 drive modes mentioned earlier by Kirk Wallace, and it does appear that you could directly drive the L298 with a single phase energized at a time "wave drive" sequence such as "step type 5" shown at Stepgen, PWMgen, Encoder

So, presumably you could use the 5-axis breakout board to access the appropriate pins of the parallel port and hook them up to the corresponding inputs of the L298. You would need to use four pins of the parallel port per axis (instead of 2), and so your breakout board would no longer be a "5 axis" board in that application. (ignoring the axis enable function)