Author Topic: Underpowered Y axis  (Read 3619 times)

Offline chuckeroo

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Underpowered Y axis
« on: October 17, 2019, 20:51:36 pm »
I bought a couple of of nema 23 kl23h2100-50-4bm. Using them on the y&a axis for the gantry movement. Best speed with a 3/8 upcut spiral is around 50 ipm. I really need to bring this speed up to 100 ipm. Thinking about using 2 clearpath servos on this axis. Used an online calculator and came up with 38 watts for a 200 pound gantry. Is this correct?The cheapest servo they sell is 38 watts and thats per unit . point being if i have 2 on this axis it should be 76 watts right? Which should take care of my problem plus quite a bit of wiggle room? Lastly how do i verify how many watts the kelling is putting out. Thanks .Thing is i have spare 48 volt power supplies and the motor mounts are in place as we speak. Hmm just occured to me i didnt factor in the load of the bit cutting the wood unless this is already factored in?
« Last Edit: October 17, 2019, 21:04:58 pm by chuckeroo »

Offline Bob La Londe

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Re: Underpowered Y axis
« Reply #1 on: October 17, 2019, 22:11:23 pm »
What is your drive mechanism.  Ball screw, acme screw, rack and pinion, other? 

Typically steppers produce their best torque at lower RPM changing your gear ratio may just do the trick for you. 

The only objective way I know to measure a stepper is at full power stationary with a torque wrench. 

I have gotten 80IPM rapid 60IPM out of 352oz/in steppers with 20tpi V-leads.  20TPI is insanely slow for a lead screw, and V-leads have a lot of friction loss.  My machines with 5mm ball screws and much larger steppers aren't all that much faster though.  They rapid at 150IPM and cut at up to 110IPM pretty reliably. 

The really fast stepper driven CNC routers I've seen with 1200IPM rapids are pretty low resolution with fast drive mechanisms like rack and pinion.  Accuracy and repeatability of around .003 to .005 and resolution only as good as about .002. 

I do have one little ball screw CNC router I tested at over 600IPM with 352 oz/in motors, but it would slowly lose steps at that speed with decent acceleration.  I turned it down to 200IPM and 25iss acceleration and it is fair to middling. 

The super fast machine with good resolution, good acceleration, good accuracy and repeatability, and decent weight and rigidity are all running big servo motors.  That being said.  My one machine with some pretty massive servo motors isn't in that speed class. 
Getting started on CNC?  In or passing through my area?
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Offline chuckeroo

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Re: Underpowered Y axis
« Reply #2 on: October 17, 2019, 22:49:25 pm »
It's a rack and pinion 3 to 1 belt drive system. 1" pitch circle 20 pitch and 20 degree  pressure angle. They only offer 2 1 for 1/4" and 1 for 3/8" shaft and the reduction doesn't change that much, very little actually. I would have to get something custom made which i'm sure would come in a whole lot cheaper than $ 600.00. i do like the way that you think though. Damn right i'd pay someone to make these. I'd also have to calculate and source a new timing belt. they offer a STEP file and an IGES file on their website, attaching these files is prohibited on CAMBAM site. CNCROUTERPARTS Standard rack and pinion will get you there. Thanks for the response! Also a torque curve the little motor create's. After thinking about this bet i could change the motor pulley and desired results.
« Last Edit: October 17, 2019, 23:37:31 pm by chuckeroo »

Offline Bob La Londe

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Re: Underpowered Y axis
« Reply #3 on: October 18, 2019, 02:45:51 am »
How about getting different gears depending on whether you need high-resolution or high-speed.  Then you can have two machine profiles.
« Last Edit: October 18, 2019, 02:52:56 am by Bob La Londe »
Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

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Offline chuckeroo

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Re: Underpowered Y axis
« Reply #4 on: October 18, 2019, 14:41:00 pm »
Well i got in touch with SDP/SI and he gave me a couple of options . The belt and pulley will be ordered today and will give this a try. Very helpful people by the way. Highly recommended! Thanks for planting a seed BOB.Thanks

Offline Garyhlucas

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Re: Underpowered Y axis
« Reply #5 on: October 18, 2019, 23:02:45 pm »
My CNC has Nema 34 960oz/in steppers with 80 volt drives fed from 67 volt linear power supply driving 5mm pitch ball screws microstepping with 32 microsteps.  All axis do 300 ipm rapids all the time and I cut at 100 ipm when the material allows with no steps ever missed.  Just providing you a reference point.
Gary H. Lucas

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Offline Bob La Londe

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Re: Underpowered Y axis
« Reply #6 on: October 21, 2019, 17:12:59 pm »
Coincidentally I have also been trying to cure a Y axis issue.  The Y-axis on my machine moves a heavy saddle and table.  (Over 1000bs)  With my old servo controllers I killed a couple drivers before going to a better servo driver.  Its been an ongoing issue for a number of years.  After upgrading the driver I used it for a couple years before cooking the servo motor.  After replacing the servo motor it seemed to work fine, but I took the time to check out the heat.  It was getting so hot that it was painful to touch, and would burn you if you held your hand on it. 

I realize the new motor may already be damaged, but it does still work.  My next solution is to try gearing it down.  It was driving the ball screw with a 1:1 timing belt drive.  I played with the available space, used an on-line pully calculator, and modeled in CAD to double check.  I found a timing pulley combination that allows me to change from 1:1 to 2:1 and use the same timing belt within the adjustment of the axis.  My only concern is the reduced engagement.  It had 11 teeth engagement before.  Now the smaller pulley will only have 6 teeth fully engaged.  Still if I just have to replace the timing belt every few years I'll be happy.  Its a lot cheaper than a servo motor. 

My new pullies should arrive tomorrow. 
Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

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Offline lloydsp

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Re: Underpowered Y axis
« Reply #7 on: October 21, 2019, 17:31:01 pm »
FWIW, Bob, the lower tooth-engagement timing pulley is also the lower torque pulley of the two.

I'd bet it will be fine!

Lloyd
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Offline Garyhlucas

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Re: Underpowered Y axis
« Reply #8 on: October 21, 2019, 17:56:28 pm »
Lloyd,
Not to argue but that is not correct. Belt tension is the same on both pulleys and that load is shared by the teeth in contact  on each pulley so the teeth on the smaller pulley always see higher shear load.
Gary H. Lucas

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Offline lloydsp

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Re: Underpowered Y axis
« Reply #9 on: October 21, 2019, 18:57:41 pm »
Ahh... thanks, Gary.  It's 'intuitive' that the torque on the motor will be half, but I didn't think of the belt tension!

'Always more to learn!

Lloyd
"Pyro for Fun and Profit for More Than Fifty Years"

Offline dave benson

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Re: Underpowered Y axis
« Reply #10 on: October 22, 2019, 03:29:20 am »
BOB
If you find that these new belts are not up to par, and can go no wider in belt size because of lack of space
then consider belts\pulleys with this profile. Among other things these belts carry more load per belt width
that standard type profile belts.
The early demise of your Motors and controllers can be many things including under spec'ed system,mechanical
binding misalignment, or even a setting in the driver, have you checked the usual suspects.
Dave

Offline chuckeroo

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Re: Underpowered Y axis
« Reply #11 on: October 22, 2019, 16:05:23 pm »
Well i thought i was going to order a week ago but  didn't, rechecked the numbers and came up with something in stock and i used their online calculator with some coaching and success was finally reached ! YEA! John is the fellows name at SDP/SI that heads up the engeneering phone calls. I was told that with my selection that torque would increase while speed will suffer. I really have no interest in doing 1000 IPM for rapids.Though i do need the additional torque.If for some reason someone else has pulled the silly mistake that i have iv'e got pulley and belt numbers in this post. This will double the torque!!  Pulley number is  A 6A53-040DF0908 and belt number will be A36R53M098090 this belt is a HTD series and a little better than the GT2 series.And it is in stock. And yes this is a CNCROUTERPARTS 4848 CNCRouter setup.I will post back in a week or so and inform you of results . Hopefully i'll get back to producing chips instead of dust and the bit life is what is to be expected. Hope this helps someone else out besides myself.Thanks for all of the discussion on this subject from everyone that chimed in! OH yes this is for the 1/4" shaft 20 tooth original pulley NOT the 3/8" shaft!!!!!!!!!!!
« Last Edit: October 22, 2019, 17:06:46 pm by chuckeroo »

Offline Dragonfly

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Re: Underpowered Y axis
« Reply #12 on: October 22, 2019, 19:54:44 pm »
@chuckeroo
My personal experience tells me that Nema 23 (47 mm between flange holes) are too weak except for a light duty engraver.  Not to speak about other factors like microstep settings, motor voltage and inductance, motor current and not last - the ability of a particular driver to provide optimal control.

Offline chuckeroo

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Re: Underpowered Y axis
« Reply #13 on: October 23, 2019, 12:42:52 pm »
In about a week the new part's will be in i will chime in after installing them. I guess we will see how long this will last.

Offline dave benson

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Re: Underpowered Y axis
« Reply #14 on: October 23, 2019, 12:48:35 pm »
Chuck I went and had a look at the website.

It's a Legit Company and they have not told any 'Pork Pies' regarding the specifications.
If you build a machine from their parts catalogue, it should perform to these specifications, without a problem.

So if you use 420 oz\in motors that they do (1 for each side) and that leadshine 4 axis drive you would be on track to a solid build Motor\Driver wise. seeing as you have 570 oz\in motors  you're OK.

Chuck, you have overspecked their 'minimum spec machine' motor wise  and if you use either  Gecko's or Leadshines Drives (both ok) then I don't see the need to gear it down it may even be counter productive.
 
look at the squareness Alignment of the table as well, this has to be as good as you can get it, and it's worth the time and effort and will pay you back in spades. The other important thing is to home it properly  so as not to introduce any racking from the get go.

Our very own Eddy has a Build Blog over at http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy of his
router, well worth a read as they discuss many things that you would find relate to your build.

Good luck Chuck, you should have some fun with that router.

Yes Fly It seems to me that for new people to the cnc scene, that there are a bewildering number of factors to take into account when building from scratch.
This might help with setting your drive re-guarding  the microstep settings.

There is property of open loop stepper motors (caused by coil resistance imbalance in the manufacturing process)
That means that they have step angle error, for a typical motor this is +- 5%  so 1.8 Deg +- 0.09 Deg of uncertainty.
When you microstep you are successively slicing up the 1.8 Deg into smaller and smaller segments and you would have guessed by now that at some point the Step Angle Error will become significant and you could no longer say with any degree of certainty that  the motor is actually pointing where you think you have it. This is the point where you must consider a servo drive, what is this point ? Well its By 10 microstepping this is what this manufacturer and gecko and  others recommend for this and other reasons, another being that as you microstep down further and further you lose some drive efficiency and this can add up.  You can set your stepper motor driver to greater than X10, but this is for system smoothness,  you can't claim any better precision though because of this degree of uncertainty caused by the step angle error.
Stepper motors are a good choice if you know their limitations and work within their performance envelope.
A similarly sized Servo System will out perform the stepper in every metric but price.
sorry for the long post chuck.
Dave