New setup, can't move A4988 steppers.

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16 May 2012 13:23 #20143 by andypugh
pfred1 wrote:

What kind of drives were you using? Color me extremely interested.

I am using some of the fairly generic ones:
www.zappautomation.co.uk/pm542-microstep...p-5.html?cPath=9_3_4
I suppose that these do have optocouplers at the inputs, so I wasn't taking any particular risk with my choice.
I think that the other points remain true, though.

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16 May 2012 15:57 #20149 by pfred1
Replied by pfred1 on topic Re:G rhymes with 23
BigJohnT wrote:

CptanPanic wrote:

2) Although I can move the stepper now, there is a twitch at .5Hz. any idea what could cause this?
I am using www.phidgets.com/products.php?category=23&product_id=3308_0 for motors, and www.pololu.com/catalog/product/1182 for controllers.
Thanks


Just to add a bit to what Rick said...

Unless you are using a drive like the Gecko 203v or 540 the mid band resonance will sound like a growl when your in that rpm range.

John


This is a less driver biased article about the topic:

machinedesign.com/article/how-to-take-vi...t-of-stepmotors-1122

They manage to cover the material without mentioning Gecko once. They really only begin a word with "g" every 196 words in fact. Something I find somewhat remarkable.

pfred1@buck:~$ echo `tr ' ' '\n' < resonance.txt | wc -l`/`tr ' ' '\n' < resonance.txt | grep ^[g,G] | wc -l` | bc


Where as John uses a "G" word every 14 words:

pfred1@buck:~$ echo `echo "Unless you are using a drive like the Gecko 203v or 540 the mid band resonance will sound like a growl when your in that rpm range. " | tr ' ' '\n' | wc -l`/`echo "Unless you are using a drive like the Gecko 203v or 540 the mid band resonance will sound like a growl when your in that rpm range. " | tr ' ' '\n' | grep ^[g,G] | wc -l` | bc

Which is oddly the square root of 196! I'm sure there is deep significance here ... I've got my eye on John. I'm waiting for him to drop the M bomb now!

The preceding public service announcement has been brought to you by bash, and Debian GNU/Linux. Strangely the G in GNU has no meaning either.

P.S. tinyurl.com/2ylpht/

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16 May 2012 17:22 #20153 by pfred1
andypugh wrote:

pfred1 wrote:

What kind of drives were you using? Color me extremely interested.

I am using some of the fairly generic ones:
www.zappautomation.co.uk/pm542-microstep...p-5.html?cPath=9_3_4
I suppose that these do have optocouplers at the inputs, so I wasn't taking any particular risk with my choice.
I think that the other points remain true, though.



They all do. This much I know, and a few other things about PWM choppers besides :)

Those Polou "drives" are better named chip carriers. They're missing a few essential components to make them useful in a CNC setup.

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16 May 2012 17:51 #20155 by pfred1
Rick G wrote:

2) Although I can move the stepper now, there is a twitch at .5Hz. any idea what could cause this?


Not exactly sure what you are saying here by twitch. You will find that steppers have a tendency to vibrate at low speeds, with one particular rpm range much worse than others.
Again play around with the timing, check the amps are not set too high.
Glad to hear you are making progress.

Rick G


The band called and you're out



But seriously now I have tried to find out what their current is set at. I don't think it is their biggest issue, I do believe it is a factor though.

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17 May 2012 01:23 #20164 by CptanPanic
According to what I read, I have turned the VREF POT to .6V, so that the current should be 1.5A.

Also when you say to increase the base period max jitter setting, how high should I set it to?

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17 May 2012 03:35 #20166 by pfred1
CptanPanic wrote:

According to what I read, I have turned the VREF POT to .6V, so that the current should be 1.5A.

Also when you say to increase the base period max jitter setting, how high should I set it to?


Not the jitter. You should be OK with what you set. These numbers are in the section above jitter. It is labeled "Driver characteristics:" In your first post you said you have your Direction Hold/Setup = 200000 Maybe I'm reading the data sheet for your driver wrong but it seems to say to me that it only needs 200 ns which is pretty fast? Your time and space set at 1,000 are right at the driver minimums. So just for laughs maybe double those and see how they work? Your best step time and space are likely going to be either where they are now or somewhat higher. But drop that Direction Hold/Setup down because it looks way off to me. Although honestly Allegro saying it is 200ns doesn't sound quite right either. I think there you're just going to have to try different values and see what works best. I'm getting all of these numbers from Allegro's data sheet for the IC in your driver BTW. All of this is in Figure 1. Some interpretation of numbers in "Figure 1." has to go into "Driver characteristics:"

You never measured the current your driver is drawing? If you have a multimeter with a 10 amps scale you should be able to hook it up and verify if your 0.6 Vref is giving you your expected 1.5 amps.

All of this configuring can be a bit of a pain but once you're dialed in you should be OK.

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17 May 2012 10:43 #20170 by andypugh
pfred1 wrote:

In your first post you said you have your Direction Hold/Setup = 200000 Maybe I'm reading the data sheet for your driver wrong but it seems to say to me that it only needs 200 ns which is pretty fast?


It is worth noting that you only ever reverse the motors at zero speed, so there isn't anything to be gained from shaving down those numbers.

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17 May 2012 13:14 #20173 by CptanPanic
But yeah looking at the data sheet again, I didn't notice that the setup/hold time were in ns, so yeah I was 1000 off. But I guess you are saying these don't matter. I will increase the timing on the time/space, and also really measure the current. And let you guys know.
Thanks.

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17 May 2012 14:07 #20174 by pfred1
andypugh wrote:

pfred1 wrote:

In your first post you said you have your Direction Hold/Setup = 200000 Maybe I'm reading the data sheet for your driver wrong but it seems to say to me that it only needs 200 ns which is pretty fast?


It is worth noting that you only ever reverse the motors at zero speed, so there isn't anything to be gained from shaving down those numbers.


What I note is that it is in the software and a universal specification. So it has to have some significance.

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17 May 2012 14:19 #20175 by pfred1
CptanPanic wrote:

But yeah looking at the data sheet again, I didn't notice that the setup/hold time were in ns, so yeah I was 1000 off. But I guess you are saying these don't matter. I will increase the timing on the time/space, and also really measure the current. And let you guys know.
Thanks.


Allegro may have typoed, or something there. Because 200ns, well it is a lot faster than their spacing. There is something going on there that bears closer examination. But you were 1000 times off. Andy says it doesn't matter, and he may be right. But I can't see how it can hurt to change the number if he is right. This may be a case where no one is right though. Me, I'm keeping an open mind on the subject. I'll let you, and the motor have the final say for what is right.

Set it all at 2000ns and see how that works, then go up, or more likely down, from there. When you're happy I'm happy.

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