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Author Topic: Motion controllers - Take me to school  (Read 5126 times)

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Offline RICH

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Re: Motion controllers - Take me to school
« Reply #50 on: September 09, 2017, 05:09:26 PM »
Quote
"Whats your opinion on closed loop steppers?" :)

Teacher responds:

That is a very good question Grasshopper, but, since you didn't do the homework ( reply #36) like all the other students did, go sit in the corner of the cave with your candle and envision $400 + for one ball screw, the whipping of the existing screw at 30 ipm, not being able to hold tolerances because the existing wimpy screw may have  antibacklash nuts that need constant adjustment.

Now go sit in the corner and think about it all....and remember Grasshopper:

You can have anything off the shelf your heart desires but once you choose it
you must pay for it. Some times that which one envisioins may not be a complete truth.  ::)

 ;D
RICH

Offline sn96

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Re: Motion controllers - Take me to school
« Reply #51 on: September 09, 2017, 05:21:23 PM »
Quote
"Whats your opinion on closed loop steppers?" :)

Teacher responds:

That is a very good question Grasshopper, but, since you didn't do the homework ( reply #36) like all the other students did, go sit in the corner of the cave with your candle and envision $400 + for one ball screw, the whipping of the existing screw at 30 ipm, not being able to hold tolerances because the existing wimpy screw may have  antibacklash nuts that need constant adjustment.

Now go sit in the corner and think about it all....and remember Grasshopper:

You can have anything off the shelf your heart desires but once you choose it
you must pay for it. Some times that which one envisioins may not be a complete truth.  ::)

 ;D
RICH

But but but.... Ok, ill go sit in the corner. :D
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP

Offline sn96

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Re: Motion controllers - Take me to school
« Reply #52 on: September 09, 2017, 05:58:28 PM »
Hi Mike,
whether you use ordinary steppers, closed loop steppers or servos is not that important, any of these devices can do the job.

If ger21 is correct that your lead screws are 1/4 diameter then the speed at which you can rotate them before resonance is limited,
additionally they will flex torsionally for a loss of accuracy and if you up the torque the problem gets worse.

Look at your machine and see if you cant replace those lead screws with, ideally ground ball screws (really really expensive),or
rolled screws. Ebay has zillions of them, go for 16mm ones if you can get them to fit. They typically have a pitch of 4,5 or 6mm
so to spin them at 1000 rpm means rapids of 4m, 5m or 6m per minute, very useful.

If it proves impossible to replace your existing lead screws then significantly increasing the speed of your machine will be limited.
Under those circumstances better specified but otherwise standard steppers with decent drivers and a 68V+ power supply would easily
provide an increase in speed up to the resonance limit of the machine whilst conserving you budget. You could certainly achieve similar
results with servos say, they would cost a lot more and you will still only be able to turn up the wick to the limit imposed by the
mechanics of your machine not the capability of the servos.

Craig

Thanks very much for the information. Yes, I never intended to go full bore with the servos because of the limitations of the machine. I only wanted to be able to have quiet motors that can swiftly do rapids (within limitations of the machine of course) without loosing steps. I think after all the input from everyone, steppers are going to be the best option in this case. I guess I will just have to endure the "wrrreeeeerrrr" noise and settle for steppers. I really don't want to go so far as to replace ball screws. Id would then consider a different machine in that case which already has ball screws like the X2 or something like that. it was my thinking that if I am going to spend close to a grand in new steppers, driver boards, and a BOB, it was worth looking into servos for a bit more money and take advantage of more speed and quiet operation. Apparently the design of my machine simply will not allow any justifiable benefit from using servos. So I have decided to do nothing and just keep my mill the way it is. For everyone who was patient enough to put up with me, I really appreciate the knowledge that was shared.
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP
Re: Motion controllers - Take me to school
« Reply #53 on: September 09, 2017, 07:15:58 PM »
Hi Mike,
seems like you've concluded that the mechanical limitations of your machine make it impractical to markedly increase its performance.
Without replacing the lead screws I tend to agree.

At the end of last year I started using an external controller, an ESS. Amongst the things I have noted is that my steppers are not as noisy,
or rather that the noise is very much less harsh. Also its possible to push them somewhat harder to accelerations and speeds which would
have caused a stall with the parallel port. These are consistent with improved pulse stream timing available from a dedicated controller
rather than your PCs CPU which has hundreds of tasks on the go at any one time.

An external controller may be a worthwhile improvement to your machine, in your case it means a controller, a BoB and either a combo
or individual drivers, not an insignificant investment. If they are chosen wisely however you will certainly be able to reuse them in your next
machine, and your post suggests you are thinking about it,... have you told your wife? I suspect with decent high voltage drivers and supply
your existing steppers will surprise you.

Craig



My wife left with my best friend...
     and I miss him!

Offline ger21

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Re: Motion controllers - Take me to school
« Reply #54 on: September 11, 2017, 08:54:34 AM »
I've found that my motors running on an AM882 drive at 1/16 microstepping are pretty quiet, when they are not spinning at full speed.
Gerry

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