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Motor Tuning in METRIC

Motor Tuning in METRIC

Postby timtitus » Mon May 18, 2015 10:17 am

Hi there,

I was just wondering if there are any Blackfoot users who have gone for the metric setup in Mach3. If so, would any be prepared to share their motor tuning settings with this tired, confused, rapidly losing his understanding on all things physical CNC-er here?

My Z axis occasionally loses steps, and whilst I have got it working to a point that I feel relatively assured this won't happen again, it feels rather slow (especially in comparison to the y axis, which has the same spec of stepper motor.)

I've checked the wiring (BiPolar Parallel) DIP switches, (co-incidentally, what is the correct setting for #8?...on or off?) and all is very healthy. All DIPS are set as per advice on BuildyouCNC.com. I've also checked to see if there are any sticking spots in the action of the Z axis...all perfect.

My Settings are as follows:
x axis Velocity:3200 Acceleration:100 1/16 Microstep
y axis Velocity:3200 Acceleration:100 1/16 Microstep
z axis Velocity:499 Acceleration:100 1/4 Microstep

So mainly, I'd like my z axis to be a bit less of a "poor Cousin" out of the three, as it seems to be letting the whole thing down a bit!
Any ideas? Thanks in advance!
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Re: Motor Tuning in METRIC

Postby kevinl » Tue May 19, 2015 3:54 pm

there should be some different in the setting and speed of the z axis in comparison to the x & y axis, there chain driven, where z is threaded rod driven.. what the spec on the threaded rod you're using..
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Re: Motor Tuning in METRIC

Postby timtitus » Wed May 20, 2015 7:57 am

Hi Kevinl, I've replaced the entire Z axis with an extruded aluminium assembly. I just couldn't get the rigidity required with the stock MDO design. It's still got the original stepper on it though, but the thread is an trapezoidal thread travelling 2mm/turn. I am wondering if this could be the culprit, ...perhaps I need a faster travelling screw. Also, as I've set to 1/4 microstepping, I'm surely getting an incredibly fine resolution on the Z axis. I experimented with 1/2 microstepping but the stepper sounded a little (just a little) rough, so I reverted back to the recommended setting, even though this was for the stock thread configuration. I've put a link for the Z axis spec below. Many thanks for replying.

http://www.ebay.co.uk/itm/NEMA23-125mm- ... 1771148428
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Re: Motor Tuning in METRIC

Postby timtitus » Wed May 27, 2015 11:17 am

Anyone?
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Re: Motor Tuning in METRIC

Postby Awesomeness » Wed May 27, 2015 2:04 pm

A 2mm/turn thread is a very slow one, essentially comparable to the 1/2"-13TPI threaded rod people use on book builds. You're going to be spinning that thread quite fast to get the travel you want, and stepper motors don't typically like that. Your 499mm/m feedrate is equivalent to 20ipm, which isn't too far off what a book machine uses. The screw on a BlackFoot is normally 2TPI, which would be about 12mm/turn... much faster than yours, keeping the motor RPM down.

Like always, culprit #1 is something mechanically loose. Perhaps a coupler, in your case.

You could also be hitting a resonance zone, so maybe try adjusting the settings, like going to 300 or 700 on acceleration.
If you don’t have time to do it right, when will you have time to do it over?
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Re: Motor Tuning in METRIC

Postby timtitus » Tue Jun 02, 2015 6:03 am

Thanks Awesomeness...that's confirmed what I was beginning to suspect. All couplers are good. Do you really mean 300 or 700 on acceleration?!!! Mines at only 100. Won't this create lost steps because I'm pushing the motor too aggressively?

Thanks for your views.
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Re: Motor Tuning in METRIC

Postby Awesomeness » Tue Jun 02, 2015 1:43 pm

Yes, I really mean to TRY it. One problem that stepper motors have is a "resonance zone"... non-technically, it's an RPM that the motor really doesn't like, and if you try to run at that speed it will stall and skip and other bad things. So adjusting your RPM or the acceleration can let the motor get over this RPM without "hanging out" there too long.

The other way to combat it is to add dampers, such as hockey pucks or weights. These change the mass of the system, also possibly thwarting the resonance zone.
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Re: Motor Tuning in METRIC

Postby timtitus » Tue Jun 02, 2015 5:15 pm

Thanks for clarifying that...I never did understand the basic idea of Resonance before! Good explanation.
I'll give it a go, as soon as I can.

Thanks again.
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