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Messages - sn96

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1
General Mach Discussion / Re: Motion controllers - Take me to school
« 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.

2
General Mach Discussion / Re: Motion controllers - Take me to school
« 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

3
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 09, 2017, 12:45:10 PM »
Hey guys,

The "threaded" lead screws are 1/4-20.........

Check out  how expensive good small accurate ball screws are!

So I echo #5 from my post:
Is the current machine ( basic and all components) acceptable to do 1. to 4. above as is, with with steppers, with servos?

But #5 is useless without defining the first four steps. ;)

RICH 


Ding Ding! Schools in! I'm at my desk teacher Richy!

Shoots hand up in the air:

"Whats your opinion on closed loop steppers?" :D

4
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 09, 2017, 12:15:29 PM »
Hi,
bloody hell, try to spin those things at speed and they'll whip themselves to shreds. Much more than 1 ft.lb
or 200 oz.in is likely to see them twist up like a carrot.

I think the OP may be on a hiding to nothing trying to get this machine to go fast.

Craig

No... just looking at different systems and yes more speed/performance for my machine is always welcome in my opinion. Is it practical or economical for a small beginner machine such as the Sherline? probably not, but if all I am ever going to make are small parts and if I want to spend any kind of money to improve my existing machine, why not look at other options? I don't understand the harm in that. I haven't spent a penny yet, and wont until I look at whats required, cost, and benefits (Things that are important to me). If a comprehensive servo solution is a few hundred dollars more than conventional steppers, then there may be something to consider... plausible.

5
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 09, 2017, 11:45:53 AM »
Hi Mike,
just been scanning around some of the other servo manufacturers and commonly a 400W servo has a rated torque of 1.27Nm which is equivalent to
160 oz.in. A 400W servo seems ridiculously large on Sherline mill.

My mill having gearboxes and so on is unusual and so my recommendation may likewise be way off as well. Do you have a specification for the torque of
the existing Sherline steppers? You know they work so you might say just double the torque and say 'now it'll work better'.

Craig

I believe these are the current specs. of my Sherline steppers:

Frame size: NEMA #23
Shaft: 1/4″ diameter, dual
shafts
Torque: 100+ oz. in.
Voltage: 3.2 V.
Current: 2 A
Step Angle: 1.8° (200
steps/rev)




6
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 07, 2017, 02:32:16 PM »
I appreciate all shared information from all of you. I am learning there is definetly more than what meets the eye. Ill reply more later. Im at work.



7
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 06, 2017, 09:32:57 PM »
There are not many options in the nema 23 form factor with a high torque much more than 90oz in in a 1/4" shaft configuration. There are two ratings: one is peak torque that  the motor can deliver for a short period of time, say like overcoming sticky ways as an example, and the continuous rating is how much torque it can provide continuously if you try to grip it with your hands. Steppers would just go into a "ZZZzzzzZZ" after max stall was applied, were as the ac servo would constantly try to turn the shaft with 90oz in of force even if the motor is fully stalled. This is how I understand it anyway.
The largest nema 23 servo in a 1/4" shaft  with the largest torque is this one:

https://www.teknic.com/model-info/CPM-SDSK-2321S-RQN/

Also what is neat about these servos are the built in driver boards. All you need is a pc with a BOB USB or Ethernet, and wire step and direction outputs directly to the servos.

8
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 06, 2017, 09:14:25 PM »
Hi Mike,
I notice the servo you are looking at has rated torque of 58 oz.in.  Seems very wimpy to me...don't under do it...you'll regret it each time the servo
faults. Craig

I saw the max torque was 200+ oz.in. but I see that it's short burst acceleration, and that the 50+ oz.in is continuous.  There are other models that have the max/continuous torqe in a more usable range.

9
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 06, 2017, 09:03:59 PM »


Quote
Hmm......, spend your money so you feel good, let us know how all goes!  ;D RICH

LOL you so silly. I get it... I get it. You hate the idea of servos put on a small machine where steppers would work just fine. Still doesn't change my fascination about the crazy speed and performance of AC servos.

10
General Mach Discussion / Re: Motion controllers - Take me to school
« on: September 04, 2017, 03:02:00 PM »
Hi,
to continue...the value end of the market..

https://warp9td.com/   the ESS recommended
https://www.pmdx.com/ the 411 for simplicity and price the 424 for increased functionality
https://www.poscope.com/products/pokeys-devices/ the 57CNCd25 for simplicity and price the E57 or E57CNC for functionality

http://www.cncdrive.com/ have useful product, the simple and cheap UC100 is Mach4 capable, the larger and more functional products are Mach3 capable only

http://www.vitalsystem.com/portal/index.php have a superb reputation but useful solution start at $600.

You may note that all of the recommendations I've made are Mach4 capable which is also my recommendation. The list might be  somewhat longer for good Mach3 only
products like
http://en.cs-lab.eu/
http://dynomotion.com/KFLOP.html

Craig



Thanks for those links. I like the Model PMDX-340 that was in the second link you provided.

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