Questions on the Polulu A4983

Greetings all,
I am part of a group of 6 people at the San Diego hackerspace that will be building Mendel's with the polulu electronics. We are currently in the parts acquisition stage and are having a disagreement on the motors required for these to function properly. It is my understanding that if we use the active current limiting feature of the A4983 boards we can run motors spec'ed for 4.2 volts at 12 volts. We are looking at the kysan electronics motor [store.kysanelectronics.com]
The debate we are having is whether or not the motors will overheat if we limit them to their manufacturer's spec of 1.5 amps.
I have attempted to contact polulu regarding this issue and all I got was some bs from marketing that really didn't answer the question.
So I am calling on the reprap community expertise. In your experience would these motors work? If anyone has a mendel running the polulu boards with an overvolted motor I'd love to know so I can settle this disagreement.
Thanks,
Mark

Edited 1 time(s). Last edit at 09/19/2010 05:47AM by fireraisr.

The voltage spec'd for a motor tells you the voltage needed for reaching the spec'd current. All stepper motor drivers used in RapRap limit the current to an adjustable value, so having a higher possible current doesn't hurt. Simply turn all down the potentiometer on the stepper motor driver, then turn it up until the motor works reliably.

My own stepper motors are rated 1.53 volts and don't warm up noticeable.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Yes, in fact you have to use a motor with a voltage rating substantially lower than the supply voltage for chopper drives to work properly. They regulate the current by switching the supply on and off very quickly, so with a 4v motor and a 12v supply it will be on for about 1/3 of the time and off for 2/3.

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[www.hydraraptor.blogspot.com]

Hey, thanks for the quick response.
Yeah, I thought that was the case. Hopefully I'll be joining the community of reprappers around mid-october.
Thanks again,
Mark

A guy in my group just asked how hot we should expect our polulu drivers to get. I've seen people with little RAM heatsinks around, is that adequate, or should we expect to need something bigger?

fireraisr, I fear you seek too much for possible trouble. Many people are using these drivers already and they work for them, so undoubtly you'll find a way to make use of them, too. Get started and solve problems no sooner than as they appear

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

You will definitely need some additional cooling for 1.5A as the Pololu PCB is far too small to provide effective heatsinking. I would think either a tiny heatsink and a small fan or a more substantial heatsink.

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[www.hydraraptor.blogspot.com]

Traumflug Wrote:
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> fireraisr, I fear you seek too much for possible
> trouble. Many people are using these drivers
> already and they work for them, so undoubtly
> you'll find a way to make use of them, too. Get
> started and solve problems no sooner than as they
> appear


If it were just me I would totally agree with you. However, we are purchasing in bulk as a group and as such we need to make sure that everyone is onboard. Answering these little questions ahead of time will ease any doubts and help keep the group in good spirits. It's always good to plan ahead and know what problems to expect.

Mmm.. Traumflug, what you suggest has a time and place but in a general sense, I think that is terrible advice.

We're spending close to $400 in stepper motors alone. It doesn't hurt to spend five minutes to jump on a forum and ask some questions. Five minutes spent here could potentially save us loads of headaches later on.

And on the pololu drivers. We're designing and making our own break out board. Again, spending a couple minutes to figure out what kind of heatsink is adequate, or if it is needed at all is time well spent. We are thinking about situating the pololu drivers in a way that a cpu heatsink would cool them all. It takes a lot of time to design and fab the boards- not so much to ask a question and understand the issues other people have already encountered.

And on the pololu drivers. We're designing and making our own break out board.
Sounds like a job for a new wiki page!
http://reprap.org/wiki/A4983_Breakout_Board

Mark, Thorp, you should lurk in reprap-dev. And actually, since you're devs, you should post in it. Lots of keen folk who will help on a breakout board.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

I`m curious with Polulu drivers, should they run cooler with Higher voltage, due to the shorter on time?

What we are doing would go here:
[reprap.org]

Sebastien, making changes to the wiki is a bit of a mystery to me. Both in the etiquette sense and in execution. For example, are pictures hosted to the wiki? Or should we use an external host and link? Is there a page outlining how to make changes to the wiki? There probably is, but I can't find it, which often seems to be the case. I'm not sure if it's my ineptness or the organization or a bit of both.

Is this the forum in which you suggest we should lurk: [forums.reprap.org] ?
If so, it seems to be pretty dead in there!

Sorry Mark, I seemed to derail your thread.

Not much because during the off time the current recirculates through the chip due to its synchronous rectification feature. So although the voltage switches on and off, the current through the motor coil remains fairly constant around the target value. That current flows through the chip, so produces heat during both the on and the off periods.

There is a slight difference because during on it flows through one of the high side drivers, which IIRC have a slightly higher RDSon. When off it recirculates through both low sides.

Edited 1 time(s). Last edit at 09/20/2010 01:04PM by nophead.

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[www.hydraraptor.blogspot.com]

I'm not Sebastien, but here we go ...

Quote

For example, are pictures hosted to the wiki?

Yes. There's a menu entry to the left "upload file". Use that. The upload page gives some hints on how to make use of that file.

Quote

Is there a page outlining how to make changes to the wiki? There probably is, but I can't find it, which often seems to be the case.

It's a link at the bottom of the editing page. Here it is again: [reprap.org]

For more complex things, simply look at how it's done elsewhere. Load that other page, click "edit" and you'll see the source.

Oh, and there's that "Preview" button. Helps a lot if you're not sure.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Sebastien, making changes to the wiki is a bit of a mystery to me. Both in the etiquette sense and in execution. For example, are pictures hosted to the wiki?

Yup! Click the link on the wiki page
File:A4983 Breakout Board 02.jpg
and it will ask you for an image file.
http://reprap.org/wiki/A4983_Breakout_Board

Is there a page outlining how to make changes to the wiki? There probably is, but I can't find it, which often seems to be the case. I'm not sure if it's my ineptness or the organization or a bit of both.

This should help:
http://www.mediawiki.org/wiki/Manual:FAQ#Basic_usage

http://reprap.org/wiki/Example
has lots of good examples, and
http://reprap.org/wiki/Columbus
shows what the wiki is capable of.

What we are doing would go here:
[reprap.org]
http://reprap.org/wiki/A4983_Breakout_Board may be a better place; otherwise your work may get lost in Pololu Electronics, which is kind of a dog pile. For example, right now Peer's display stuff is buried in there. It also makes your work hard to link to.

Is this the forum in which you suggest we should lurk: [forums.reprap.org] ?
If so, it seems to be pretty dead in there!

reprap-dev = super secret developer mailing list.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

I could only put about 0.5A through mine before hitting the thermal limiting. I used a video card cooler to cool 4 chips, but from what I've read, those little stick-on ram heatsinks, one per chip may be adequate.

Beware of measurements, there was only 11mm between the Vbb filter capacitor and the current adjust pot (both of which were taller than the chip needing heatsinking) on mine- sounds like you don't want to have to cut them to size...

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Wooden Mendel
Teacup Firmware