Stepstick alternative.

While looking for suppliers of Stepsticks I found out that A4988 chips are getting harder and harder to find with every passing day. This lead me to look for alternative IC's to make compatible drivers for RAMPS out of. The only IC's I can find that look comparable to the Alegro A4988 and A4983 are the Texas Instrument drv88 series driver.

From what I can tell the chips capabilities are the same or greater than that of the Alegro chips.

These are the ones I have narrowed it down to and was wondering if anyone could comment on whether they will work correctly ( different package than the A4988 but that will only require a redesigned board I hope ).

http://www.ti.com/product/drv8824
http://www.ti.com/product/drv8825Most likely to be used

Advantages to switching to these chips is higher current capacity and up to 1/32 microstepping.

Gen6 uses the little brother of these the drv8811.

Edited 1 time(s). Last edit at 06/08/2012 10:41PM by Sublime.

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The A4982 is starting to gain some following too, currently used on the Printrboard and some upcoming designs Ive seen. I did a quick board layout(pololu footprint) for it and it fits aok( TSSOP package=better heat spread). Only difference from the A4988 is that it lacks 1/8 microstepping but has 1/16.

Being stuck on the pololu footprint can be a hair puller when trying to design these chips from different manufacturers. I tried doing the DRV8811 but its using too many support components that I need to move some on the other layer. I have some samples of the 8825 from awhile back and have not tried laying them again.

The A4988 are getting snatched like crazy, Ordering them from my rep takes 18-20wks with a min of 1500pcs.

I saw the A4982 was being used on the Smoothieboard as well.

Getting the extra components on the drv8825 should be similar to the board JohnnyR made up for the A3979 [reprap.org] but you may be correct in there just not being enough room.

Is there any other reason you can think of that they may not work with our firmware or anything (looks like it requires 1.9us step width (evluation board says on 1us)).

I would also really like to see 1/32 stepping for the smoothness and noise reduction.

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Im not sure if the current 8bit controllers can do 1/32 reliably, you could always fall back to 1/16 if needed.

Looking at the 8825 again, it seems they have the motor pins on one side (unlike the 8811 that has them on 2 sides) and pin layout is similar to the allegro chip. Might be easier than I thought.

Edited 1 time(s). Last edit at 06/09/2012 02:02AM by royco.

royco Wrote:
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> Im not sure if the current 8bit controllers can do
> 1/32 reliably, you could always fall back to 1/16
> if needed.

Good point. It would reduce our max speed to half of the current with 1/16th. But that should not be a problem except for in the most extreme cases. And like you say we could always set the jumpers for 1/16th.

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The datasheet says they have a fixed frequency of 30kHz and a minimum on time of 4us. That means the PWM ratio can only go from 100% to 4 / 33 = 12%. The current table shows it going from 100% to 5%. The only way I can see that happening is if it is set to fast decay . Seems odd though that they have a slow decay and mixed decay that wont actually work in most cases. It would work at 1/8 step if the motor voltage was close to the supply voltage.

With it being fixed frequency both coils should be synchronised so there should be no beating in the audio band as there is with Allegros.

I have ordered an evaluation board to have a play.

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[www.hydraraptor.blogspot.com]

@Nophead
Do you see this as being an issue?

Should we go ahead and make up some prototypes?

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
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I don't know to be honest. If you wait a few days I will let you know well it works with 12V and a Zapp motor.

Edited 1 time(s). Last edit at 06/10/2012 05:27AM by nophead.

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[www.hydraraptor.blogspot.com]

The disadvantage of fast decay is the ripple current is a lot higher and since the driver only switches off at the peak of the sawtooth the average current is lower than the target by half the ripple.

The offset is more noticeable on the low current steps and can even be larger than the lowest step, another cause of microstepping error.

I wonder how the high spec drives that Viktor uses manage to do 256 or more levels accurately.

Edited 1 time(s). Last edit at 06/10/2012 10:28AM by nophead.

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[www.hydraraptor.blogspot.com]

if the electronics did go away from the poplu and stepstick format i would like to see it made with a keyed style pins it would make the boards a bit bigger but in time i think it might not be a bad thing to have.

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[mike-mack.blogspot.com]

dissidence Wrote:
-------------------------------------------------------
> if the electronics did go away from the poplu and
> stepstick format i would like to see it made with
> a keyed style pins it would make the boards a bit
> bigger but in time i think it might not be a bad
> thing to have.


We are talking about a new driver that plugs into the existing Pololu socket.

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I think the Melzi format is the best so far. It has much better heatsinking for the stepper drivers because they are on the main board, which also reduces the cost a lot. The connections are all screw terminals which are more reliable than push fit connectors and don't need any soldering or crimping.

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[www.hydraraptor.blogspot.com]

I do like the better heat sinking of the larger pcb but after building a bunch of machines and helping others I have seen far to many burnt out drivers to ever suggest a set of monolithic electronics to anyone. I and others I know have also had Arduino's die, some new and some after months of use. So being able to replace each component individually is really nice. And now with the arduino Due coming RAMPS users will be able to upgrade to 32bit without much cost (once the firmware is there). I also find the current size/shape of Melzi is really inconvenient for enclosing or even mounting in most cases.

An idea that was mentioned to me to reduce cost was to make the drivers part of the board but be able to snap them off if they die and connect new ones. Sparkfun has a product that works like this [www.sparkfun.com] .

Edited 1 time(s). Last edit at 06/10/2012 08:41PM by Sublime.

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To add to that, boards having drivers built-in wouldn't have the ability to use new/improved/updated drivers as they show up. Production would also be tied up to a chip that is not easy to get and has long lead times.

Also, there are a lot of users out there who prefer push fit over screw terminals because of loosening screws when the board is mounted on the printer. Altho I prefer screw terminals myself and hate to do crimping.

@sublime - The RAMPS would probably not work on the Due since it is on 3.3v instead of 5v (not enough to fully drive the Mosfets)

Edited 1 time(s). Last edit at 06/10/2012 08:52PM by royco.

royco Wrote:
-------------------------------------------------------
> @sublime - The RAMPS would probably not work on
> the Due since it is on 3.3v instead of 5v (not
> enough to fully drive the Mosfets)

I did not know this. We could make a shield with cmos/ttl converters to go between them as a work around for people upgrading.

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Discreet components can take of the mosfet drive, most important is that the current firmwares need to be compatible with the latest release of Arduino to compile properly with the Due( when and if it comes out)

Quote

Also, there are a lot of users out there who prefer push fit over screw terminals because of loosening screws when the board is mounted on the printer.

I find exactly the opposite. Push fit connectors are unreliable and develop high contact resistance and burn out when subjected to the vibration of the machine. Screw connectors don't work loose. As I have run machines 24/7 for years I have found connectors to be one of the main sources of unreliability.

I have also never had a stepper drive fail despite setting VREF too high, inserting one the wrong way round, having loose motor wires and latching them up with ESD. I did manage to destroy an expensive one on HydraRaptor by connecting the mains to my micro controller [hydraraptor.blogspot.co.uk]. I think that incredible bad luck put me in credit for good luck ever since.

Two of the failure modes are getting too hot, which would be less likely / impossible with the right heatsinking and VREF limit, and inserting them the wrong way, which would also be eliminated. Current limiting the 5V supply to them and possibly adding some transient suppression diodes should make them bomb proof.

Electronics are better designed not to fail rather than being socketed so you can replace bits that do fail. That ended with valves (vacuum tubes).

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[www.hydraraptor.blogspot.com]

IMHO, a good reason for push fit connectors are, you can unplug and re-plug a motor without making a headache on the wiring. Sorting these four wires each time isn't exactly convenient.

If the machine vibrates too much - well, then put the electronics seperate or mount it with something soft.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Traumflug Wrote:
-------------------------------------------------------
> IMHO, a good reason for push fit connectors are,
> you can unplug and re-plug a motor without making
> a headache on the wiring. Sorting these four wires
> each time isn't exactly convenient.
>
> If the machine vibrates too much - well, then put
> the electronics seperate or mount it with
> something soft.

I believe Phoenix Contact makes some screw terminal blocks that terminate in a plug, and a matching PCB receptacle. Best of both worlds, but pricey.

As for replacing the Pololu form factor, I like Sublime's idea of using snap off modules. Matching holes could be provided on both sides of the snap so shunts could be installed for replacing a broken module. Additionally, the motor connection, however it gets done, should be directly on the module itself and not route through the mainboard.

Alternatively the drivers could be mounted perpendicular to the mainboard with the motor connector coming off the edge. Think PC card slots, but without a bracket. If all the driver boards are coplanar, it would be easy to stick a tiny fan at one end and keep the lot cool. And it should be easy enough to design a printable "card cage" to keep the top edges even and direct airflow. The only downside I could think of is adding height to the electronics.

@ Nophead

Have you received your evaluation board? Does it work?

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Yes I got it a while ago. I haven't had time to try it yet but I will do hopefully this week.

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[www.hydraraptor.blogspot.com]

(thread hijacking)

EDIT: Ok sorry maybe I wasn't following this section of forum closely...I found a few mentioned in another threads.

What is the availability of Toshiba's TB6560 in the western? There are plenty of supply in China - selling at around 3 USD each.

The footprint is not small - the chip itself is as big as the polulu shield, and requires a big resistor for current sensing. It features 16 microstepping, didn't mention anything about fixed off time (I assume none like L298 hopefully?), and various decay mode, plus idle current limit % that Allegro doesn't have. And it could handle 3A current (operational). To me it's quite an attracting chip, but I don't really see it being mentioned in reprap community.

I already had the 3-axis powered by TA8435H (an older generation with less featured packed) with "cheap China CNC 3 axis driver" product, so far so good. I am getting a TB6560 board for the extruder. I think it worth to give a try if it's available in US/Europe, given the status of the Allegro's.

Edited 1 time(s). Last edit at 07/15/2012 09:47AM by sam0737.

@ Sam

Down about ten threads in this section you will find [forums.reprap.org]

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@Nophead

Im interested to know if it works as well. Thanks.

I am building a Mendel Prusa, my first ever 3D printer build. I've decided to use push connectors for the motor to stepper board which are polarized and have a latch. Digikey links:

[www.digikey.com]
[www.digikey.com]

3DMD Wrote:
-------------------------------------------------------
> I am building a Mendel Prusa, my first ever 3D
> printer build. I've decided to use push connectors
> for the motor to stepper board which are polarized
> and have a latch. Digikey links:
>
> [www.digikey.com]
> [www.digikey.com]

Those look nice. A bit expensive, but probably better than standard Molex connectors as you don't have to worry about them coming loose.

Edited 1 time(s). Last edit at 08/05/2012 07:09PM by NewPerfection.

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Is there any reason why the A3979 carrier is unsatisfactory?

It would appear to be a valid stepstick alternative.

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Leo

leo@RepRapKit.com
[RepRapKit.com]

FWIW: Some of you may have seen this around the traps, but it might explain the sudden shortage of Pololu boards people have commented on:

New "Black Edition" Pololu A4988's with better thermal heatsink capacity.

[www.pololu.com]

Not a huge improvement, but it's better than it used to be (and 99% probable that it was the 3D printer market that forced this change to the carrier design). Whether it is too little too late for Pololu is another thing entirely.

Note: Same sort of shortage happened with A4983's just before the A4988's appeared on the market.

Its a good thing to see them trying to make a better product.

But to get much more power from a ramps board I think it would need a pretty big foot print and redesign.

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[mike-mack.blogspot.com]

out of curiosity .... i would be v interested to try 1/32 ... :p
i even ordered samples (wad the hell m i thinking :p )

Edited 1 time(s). Last edit at 10/22/2012 08:14PM by redreprap.