Mod for Stepper motor driver Board

From the wiki

"The L298 is rated for 2A per coil, so if your stepper motor drives more than that, you should adjust the chopper so that it delivers less current than that. "

"Bipolar - Parallel
This configuration offers higher performance. It has lower impedance, and lower resistance. That means you can push more electrons through, at a faster rate. That basically means it will operate much better. However, it will draw about 3 amps, which our L298 is just not capable of delivering. We do not recommend wiring it like this. "

Wouldn't it make more sense for the L298 to drive a power mosfet? Then we could use motors that draw much more current. Something like the irf540 would work up to 33amps as an example.

Mike

That would only allow the motor to be switched on and off (not reversed). In order to reverse a motor you need to control it from an h-bridge (http://en.wikipedia.org/wiki/H-bridge). One could be made using 4 irf540s but they can be tricky to get right, and an off the shelf h-bridge like the l298 has some nice extra features. Someone may wish to design a high power board, that is compatible with the current one. It would also be much cheaper as those L298s are pretty pricey for what you get.

You run into a hell of a lot of issues with gate voltage levels. In the end you need complimentary P/N pairs or a bunch of different voltages and level converters.

I tried building something like this but it kept frying the transistors :-(

chopping seems to be aggressive to the circuits as well.

I'd stick with ready mades all the time. Motor drivers are just not worth the trouble unless you are an expert!

He's right.

I should have mentioned before: you only need h-bridge motor drivers for bipolar stepper motors. Unipolar motors would run happily from 4 power mosfets, simply one for each coil. You would need some more output pins from the arduino (that don't exist), and to modify the firmware though.

know any stepper drivers that can do 3-4 amps then?

This guy is bridging the two channels on a l298 to get a single 4A channel [www.ikalogic.com]. You would need two l298s per motor then though.

You can buy off the shelf h-bridge boards e.g. [www.active-robots.com]

Edited 1 time(s). Last edit at 07/09/2008 08:40AM by greenarrow.

Hello,

I feel that the Circuits, Stepper motor application of Cypress is really impressive and best when put to use. I have tried it personally, n felt so. check it at [www.cypress.com]

Is this what you are referring to?

[www.cypress.com]

If so using a unipolar stepper does make the electronics simpler, but they tend to be less efficient and so larger / more expensive for the same power output. So I'm not sure the electronics + the motor would work out cheaper, just a different balance of where the money went.

If you are interested in larger motors then could I suggest looking around CNCZone. Machining requires larger forces than reprap does, so I'm sure there will be plenty of people using quite large motors.

There are a couple of h-bridge chips that will deliver considerably more than 2 amps. I got interested in that idea and ran them down on the web about 6-8 months ago. One is even pin compatible with the L298 and a LOT smarter inside. As you might expect, they're more expensive, though. Mind, not nearly as expensive as buying a higher capacity stepper controller board commercially.

I think that you have to ask yourself one very important question, however, "why are you designing a positioning system that needs so damned much amperage?"

If you select the right stepper motor you can run Darwin on 0.5 amps at 12 v per motor. The L298N is way overpowered for that. The 57BYGH320 from...

[www.cw-motor.com]

...costs about $20 and pulls a 0.4 amps. The price you pay in in a heavier motor. It weighs about a kilogram but will power a Darwin with minimal energy beautifully.

For my part I've been trying to evolve a minimal materials mass reprap machine. Instead of belts I'm using linear steppers...

[www.hsi-inc.com]

I use two sizes of these kind of steppers on my Tommelise 2.0 reprap machine, the Haydon 26000 series and the Haydon 36000 series. They weigh 15 and 40 grammes respectively and provide enough thrust to push over six pounds around on the xy positioning table at ~16 mm/sec per axis.

Extruding plastic doesn't put much stress at all on the object being printed. Positioning doesn't require a tithe of the robustness of what you require for CNC milling. A lot of people interested in Reprap seem to be keeping in their secret hearts the notion that if they finesse things just right they will wind up with both a 3D printer AND a workable CNC machine positioning system. If that is what you really want I'd suggest that you take a hard look at what Nophead has put together in that regard on his blog...

[hydraraptor.blogspot.com]

He makes it happen and you can see what it takes. His original bootstrap printer is plenty robust enough for milling, but is massively overdesigned for 3D printing. That's not a criticism, mind. His machine works beautifully and he has leveraged it to do a lot of groundbreaking work on getting plastics warping down and improving the surface quality of prints.

In reply to [forums.reprap.org]

Forrest Higgs Wrote:
-------------------------------------------------------
> There are a couple of h-bridge chips that will
> deliver considerably more than 2 amps. I got
> interested in that idea and ran them down on the
> web about 6-8 months ago. One is even pin
> compatible with the L298 and a LOT smarter inside.
> As you might expect, they're more expensive,
> though. Mind, not nearly as expensive as buying a
> higher capacity stepper controller board
> commercially.

Whats the pin compatible IC? I'd be interested in seeing its datasheet

> I think that you have to ask yourself one very
> important question, however, "why are you
> designing a positioning system that needs so
> damned much amperage?"

I'm building a star tracker using two stepper boards and motors, my telescopes a lot heavier then my mill!

Quote

I'm building a star tracker using two stepper boards and motors, my telescopes a lot heavier then my mill!

Ahh, suddenly this all makes a little more sense

I always assumed that star trackers would use a lot of gearing and some modestly sized, fast DC motors. Or even a lot of gearing and some steppers. Most scopes I've ever had the chance to play with were very nicely balanced and required very little force to reposition.

Or are you not using an equatorial mount?

I'd suggest you take a quick look at the...

LMD18245

which delivers 3 amps and is pin compatable with the L298N. It is also a lot more sophisticated than the L298 and does it's own current sensing, iirc.

There is also the

L6205n

which delivers 2.8 amps and in a standard PDIP configuration.


There was one I ran across that would deliver either 5 amps or 8 amps. I wasn't able to track it on short order, however.

It's an old cheapo scope, I'ld like to start with telling the scope to point at jupiter (or whatever), if theres shaking while following it i'll add gears. When I get a new scope my goals to spend the money on the optics, and build tracking and imaging myself. It's just a spare parts project now, to get the basics of it working.

Quote

LMD18245

The [avrstmd.com] uses this h-bridge, so you could get a pre-fabbed solution to your problems. He sells kits, I believe, but the schematics and firmware for the controller IC are open source.

He also suggests that if you want big (5A+) motors, you should buy yourself a geckodrive to control them

I'm just trying to dig up some of my old searches and sites on the subject of motor controllers... I really should have bookmarked it all as it is proving to be rather difficult to find again. So far I've only found the [www.fromorbit.com] picstep, which has much the same sort of power as the STMD.

Quote

I'ld like to start with telling the scope to point at jupiter (or whatever), if theres shaking while following it i'll add gears

That's pretty much guaranteed, isn't it? You need continuous, slow movement to track precession and stuff. Even microstepping, I'd be startled if you didn't see the motors 'tick'.

Hi everyone,

I need sine help for L6205N H-Bridge. T tried to use a L6205N to control 2 motors, but i have hard time to build a circuit. I did just like what they tole me to do in the datasheet. However, when I have to 12 v to Vs and 5V for Enable A and B. Without the signal input, I still have 12V for all 4 outputs. I tried to replace the chip, capacitors, diodes but just the same result.

If anyone know what wrong please help me out.
Thanks

Hi Mike,

... AFAIK if you haven't connected a motor, your outputs will have the max. voltage.

Only if you burden the outputs, the circuits can regulate the current through the sensing resistor ...

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I'm still not sure why anyone needs to have high current drive for RepRap steppers. Using 1A NeMA 17 steppers for the XY and Z axis is more than adequate for speed and tourque.

Even extruding using a worm gear extruder drive a 1A stepper is quite adequate.


Now for a CNC machine yes you will need much higher power steppers but Mendel and Darwin work ok very nicely with only 1A drivers.

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