Nasty resonance / rattling - possible assembly error?

[MitchL]

Our high school has a PRSStandard that's basically ownerless (wood shop classes are no longer taught, the bot was purchased only a couple of years ago and seldom used).

We (school's robotics team) have basically inherited it.

I am starting to wonder if it was assembled correctly (the limit switches weren't correctly installed, for example).

There's a nasty rattling noise that you can hear in the following video:

http://www.youtube.com/watch?v=5IB2NeJ2ktI

The video is an air cut, router off, so all you're hearing are the carriage motors.

It's mostly present on the left-hand (Y+ side) X axis carriage and on the Y carriage.

- The pinions do have a small amount of dirt, but it's not terrible.
- The rattling occurs everywhere on the table, so I don't think it's rack or pinion wear (the machine's basically brand new).
- There is some backlash that's either in the gearboxes or possibly a loose set screw on the pinion.

The rattling seems to be introducing unacceptable vibrations into the cut, particularly when I'm cutting aluminum. I'm cutting at 60IPM / 0.005" per pass, so it should be a light touch from the router's perspective.


So: Should I be taking the motors off, inspecting the pinion set screw, and getting them back on nice and tight?

Any other assembly issues I should look into?

Thanks a bunch! I'm looking forward to giving our ShopBot some much needed TLC before the robotics season heats up.

/Mitch.

[MogulTx]

OHHHHH! That is awful!

Have one of the Techs from shopbot listen to this. A couple years ago, I was running a PRT that was loud and jumpy and the final diagnosis was blown Zeiner ( sp?) diode(s) on the board. This was the old style board- but bad connections (maybe incorrect connections?) to the drivers might do this to you. You might have the wrong pinion gears on the motors ( z is often different from X&Y and one may have been installed on the wrong motor?)
But it sounds awful- and should almost hum as it is running around with the router off...


Get their professional opinions and do some check out. You won't be sorry.

[MitchL]

OHHHHH! That is awful!

Have one of the Techs from shopbot listen to this.
...

But it sounds awful- and should almost hum as it is running around with the router off...


Yeah, it hurts to listen to it. The shop is a huge echo chamber, which enhances the effect :-)

I'm a hobby CNC builder on the weekends - the machine I'm currently building is very ShopBot-like (rack and pinion, gearboxes, nema34 motors). My machine's not done yet, but my experimental carriages move smoothly and quietly with very little backlash - I figured the ShopBot should be at least as smooth!



Get their professional opinions and do some check out. You won't be sorry.

OK, i'll pursue that - I am not certain our ShopBot is still under maintenance anymore. (actually, I'm so new to ShopBot I'm not certain there even _is_ a maintenance program, but I assume so!).

I'll submit a request to support via the website and see what happens.

Thanks a bunch!

/Mitch.

[bleeth]

This sounds like a combination of ingredients.
First: SB support is for the life of the tool and transfers with ownership. So contacting them is definitely in order.

Now:
This puppy sounds completely out of level and square. You need to start by verifying the x rails are parallel, straight and level, and the correct distance from each other. You then need to move on to the y rails, and then verify that the gantry is perpindicular to the x axis. Your final step (although this issue will not make much noise) you need to verify your z is plumb.

There is ample documentation on that in the shop-bot docs (setting up your PRS) and also an article on squaring by Gary Campbell in the columns section.

It will be a very "fiddley" process, but the result is all of your v-wheels will ride smoothly on the rails and with the control box off AND the motors unplugged when pushing it around by hand. (Never push it by hand with the motors plugged in-you WILL blow out drivers). If you disconnect it now and push it around you will find you have wheels not sitting correctly in rails, binding, and generally messed up. When properly tuned the whole thing will run smoothly and quietly. When all of the above is done, then make sure your pinions are properly seated and tight, as well as not overly worn.

Oh yeah: With the motors on try to move each side of the gasntry and see if they are both on. If one side doesn't want to move, and the other does, then you have a loose pinion, or a blown driver. Motors rarely go bad.

[bleeth]

By the way: This sounds exactly like a louder version of the typical resonance that PRT's make. It is so evident in them that Bill Young, of Shopbot, wrote a program to move the tool using a "musical note" program based on a small keyboard and had them playing happy birthday for shopbots tenth anniversary.
As you are new to the forum, my machine started as a PRT standard, and over the years I upgraded it to a PRS Alpha. When it went from Old control board standard to 4g resonance got quieter, and when it went to PRS it got very low. When it went to an Alpha resonance virtually disappeared.

Do make sure all frame and rail bolts, nuts, and screws are tight.

[bleeth]

Doc links:

http://www.shopbottools.com/ShopBotDocs/files/Assembly%20PRS%20Gantry%202012%2012%2031.pdf

http://www.shopbotblog.com/index.php/2008/12/tuning-up-the-prs-gantry/

[MitchL]

By the way: This sounds exactly like a louder version of the typical resonance that PRT's make. It is so evident in them that Bill Young, of Shopbot, wrote a program to move the tool using a "musical note" program based on a small keyboard and had them playing happy birthday for shopbots tenth anniversary.

That's awesome. I've got a script somewhere that converts MIDI files into G-Code that I use to play music on my home (Mach3-based) CNC. It always amuses :-).



As you are new to the forum, my machine started as a PRT standard, and over the years I upgraded it to a PRS Alpha. When it went from Old control board standard to 4g resonance got quieter, and when it went to PRS it got very low. When it went to an Alpha resonance virtually disappeared.


Yes, I'm new to the forum, new to ShopBot, but not new to CNC. I'm here to learn how to take care of our ShopBot from the experts!

The ShopBot is owned by the school, so getting money for upgrades might not be the easiest thing to do. Worth pursuing though, just in case. We do have the newer control box AFAIK. I'm not super familiar with the differences between Standard and Alpha (will do my research) - I believe ours is a standard based on its purchase date.


Do make sure all frame and rail bolts, nuts, and screws are tight.

Will do, and will read the links you posted and do as many measurements as I can to see how level and square it is.

/Mitch.

[bleeth]

You can tell if it is a standard or an Alpha right away from the motor numbers.

Standard: 9412KTG

Alpha: ASM98AAT7.2 (Although you may have 3.6/1 and not 7.2)

[MitchL]

You can tell if it is a standard or an Alpha right away from the motor numbers.

Standard: 9412KTG

Alpha: ASM98AAT7.2 (Although you may have 3.6/1 and not 7.2)

I'm not near the machine but happen to have a close-up of the motor.

It's the standard one, model A7328-9412KTG.

Is the upgrade to the Alpha just new motors and a controller? I suppose I should contact ShopBot for details.

It's tempting to swap out the motors and switch the controller to Geckos/Mach3, but that's the hobbyist in me. Need to keep this one pure ShopBot :-).

/Mitch.

[bleeth]

Yes. I wouldn't call it "just" though. Many thousands of bucks for new Alpha motors and drivers, even if you buy them direct from Oriental and build your own control box to handle them.
You may already have Geckos. Standards are, although there is some "special" shopbot construction of them. SB3 software will run g-code, but since the design software that writes Mach also writes SB code no real reason to. A long way back, before SB started running Geckos (It's a long story) some guys built a gecko box and ran Mach and there are still a few of them out there. Some of them insist there Mach runs better than SB3, and for some of the more touchy releases of SB3.xxx they are probably right. For your machine, check your software and if it 3.6.4x I wouldn't change it. The 3.8xx has nothing in it you need and has caused some people who upgraded issues.
I ran those motors with Gecko 202's for years on SB software with no problems. Yours probably has a SB version of the 203's. The motors are custom built for SB and have Tapered hob gears built in (3.6/1)

[MitchL]

Great info, thanks!

I haven't peeked in the control box yet - my comments were basically the hobbyist in me looking at a machine to tinker with :-).

But: this isn't my machine, it's owned by a school district, and eventually my sons will graduate, meaning I'll be moving on. So, over the years if we add upgrades, they should be official ones that ShopBot will support.

I should be able to spend a little while with the machine this evening to see if it's square and true, everything's tight, etc. Will report findings.

/Mitch.

[MogulTx]

Mitch,

If you can follow Dave's suggestions, you may well be done. If not a call to Shopbot is definitely in order... and as he says- the support is for LIFE and it is pretty darn great, too.

I would not upgrade a PRS to a PRS Alpha unless you are in a production shop environment and found yourself using up all your available hours in actual cutting time. There is little opportunity to recoup the $ unless you are able to speed the machine up significantly.

For what you are probably going to be doing, this is the right machine. If anybody ever gets antsy for increased performance, a spindle ( vs the router) is probably a much better investment.

Good luck.

Monty

[Brady Watson]

That sounds like mid-band resonance, which happens to a degree on all stepper based systems, even Alphas. Try changing your move speed to something a little faster, say MS,2,1 and see how that sounds. Certain speeds will sound like that - not much you can do about it.

Without seeing your control box, I cannot see what motor drivers you have. If you have the Gecko G203 drivers, you can adjust some of the resonance out on the driver itself.

The important factor should be how the tool cuts & what the cut quality is. My original SB sounded like that, all day, every day. It made me lots of money and then I upgraded to an Alpha.

-B

[MitchL]

That sounds like mid-band resonance, which happens to a degree on all stepper based systems, even Alphas. Try changing your move speed to something a little faster, say MS,2,1 and see how that sounds. Certain speeds will sound like that - not much you can do about it.

I agree, I think this is the way it is for me. I've been in touch with ShopBot support (great service!). They had me check a few things (connectors, wires). Everything looks good.

I played with feed rates. Speeds <40IPM sound great. Speeds >90IPM sound OK, except during the curves, where the steppers need to pass through the 60IPM barrier. It just happens that around 60ipm is the good place for feed rates with a 2-flute cutter in aluminum at 10K RPM. I'll try some more experiments, like 90IPM/13K RPM.

Our controller has the Oriental Motor C006Q-044 step drivers inside, and the Oriental Motor A7238-9412KTG steppers and gearboxes on the carriages. I believe our ShopBot is pretty "plain vanilla".


Without seeing your control box, I cannot see what motor drivers you have. If you have the Gecko G203 drivers, you can adjust some of the resonance out on the driver itself.

Yep, I use 203Vs on all my home CNC builds -- my go-to standard.


The important factor should be how the tool cuts & what the cut quality is. My original SB sounded like that, all day, every day. It made me lots of money and then I upgraded to an Alpha.


You can feel the vibration in the head when it's rattling (even on air cuts with no spindle power). Since I'm cutting aluminum, and taking very light passes, it really shows in the bottom and side walls of the cut. When the resonance gets really bad, it sounds like chatter, then I start to get nervous.

Thanks all!

/Mitch.

[bleeth]

A relatively low cost upgrade would be the 4-G (Shopbot Gecko), if SB is still offering it. Their current upgrade control box, which has a lot of very good reasons to do so, uses RBK drivers and is pretty expensive. Otherwise you may be able to find someone with a 4-G available to sell you. I believe the retail price was around 1400 or so.
Go down to my earlier post on getting it all square and level, tight bolts everywhere, and make sure your pinions are in good shape. I never tried aluminum on my PRT when it had the pre-gecko control box but Brady did and will likely have a better comparison.
I have seen other PRT's that were noisier running in air than mine was originally and I am convinced it had to do with how anally cumpulsive I was about physical alignment.

[Brady Watson]

Mitch,
I am not familiar with the stepper drivers that you list. Any chance you can take a pic or two of the control box, with some shots of the drivers? I'm a little tired from driving for 9hrs today...but to the best of my current (brain drained!) knowledge, there are only 2 types of oriental drivers that were offered from the factory: The AlphaStep drivers, beginning with an "ASD-" prefix, and the more recent Standard line of tools that have non-Gecko drives, that use the "RBK" series.

So - I am a bit curious to see what you have there & can make suggestions after I see it. If these are separate from the main board, then they should be step & dir drives, which means you can most likely upgrade to either a Gecko or RBK driver with a hotter power supply to gain some smoothness, resolution and power. The one caveat is that all drives need to have the same 'common' polarity, and depending on the board you have, you can change it with a jumper.

Thanks!
-B

[MitchL]

I happen to have photos of the drivers and the steppers:

They're definitely step/dir drives, the board that attaches to the front of the drivers has signals labelled as such.

I thought I had a vanilla picture of the inside of the control box, but I don't (the main board's part number is 090704). The USB interface says "Shopbot Tools Contorller V206").

Here are the photos that are still lurking in my phone:

/Mitch.

[bleeth]

The appearance of that driver is identical to the way the RBK's look. It could be an earlier model number, a precurser to it, or a "special" number assigned to ones for Shopbot. I don't think you have any reason to change them out. Check the settings on the two dials and make sure they all match. Also let us, or SB know what those settings are to verify they are correct.
The further along we go, the more I think your frame/gantry/car alignment is out of whack or loose, and your pinions may be worn, and your motors may not be tight enough against the pinions.

I'm still betting that if you dial all of that in your resonance will go way down.

[Brady Watson]

OK - Yes, those are RBKs.

See page A265; Function Switches [2]: http://www.orientalmotor.com/products/pdfs/2012-2013/A/usa_st_rbk.pdf

It may take a little trial an error messing with the dip switches, but concentrate on one axis at a time to test for smoothing (say the Y axis). Don't fool with the dials & MAKE NO CHANGES WHEN THE POWER IS ON!!!

Start with SW2-1 and make no other changes. See if that smooths things out a little for you.

Yeah...A bit of a pain since you have to pull the main board off, but should be worth it. Take care when putting the board back on the drivers. It is really easy to bend or break pins. You are doing all this at your own risk. Be deliberate.

Post back and let me know how you made out.

Thanks!
-B

[Mayo]

At the risk of sounding obvious, before doing all the mechanical stuff,
have you verified that the unit values, speeds and ramp settings are correct?

[MitchL]

At the risk of sounding obvious, before doing all the mechanical stuff,
have you verified that the unit values, speeds and ramp settings are correct?

In this particular case, I think I'm OK. I'm just doing air cuts, spindle off.

I use Aspire 4.0 to make my toolpaths, use the standard ShopBot arcs postprocessor.

The toolpath is very simple, a 4" square with one corner rounded (about a 1.5" radius).

/Mitch.

[srwtlc]

Unit values and ramp settings are set in the control software (SB3) and not in your design/toolpath software. Along with the excellent info Brady provided for tweaking your drivers, you may want to make sure that you have the proper settings loaded for your model of ShopBot. This will also load the default unit values and ramp settings. You do this by typing in the command UR and choose to reset/reload the defaults for your tool (PRS_standard and your table size) .

[MitchL]

Unit values and ramp settings are set in the control software (SB3) and not in your design/toolpath software. Along with the excellent info Brady provided for tweaking your drivers, you may want to make sure that you have the proper settings loaded for your model of ShopBot. This will also load the default unit values and ramp settings. You do this by typing in the command UR and choose to reset/reload the defaults for your tool (PRS_standard and your table size) .

Ooh, this could be important. Thanks!

I'm obviously new to ShopBot. I installed the software and updated the firmware before I used it. I'm pretty sure I have selected the right model ShopBot, and haven't deviated from the defaults provided. Definitely something to double check.

When I hear "Unit Values" and "Ramp Setting" it just sounds like toolpath stuff :-).

Thanks everyone -- I'm getting there! :-)

/Mitch.

[jerry_stanek]

Have you tried changing the speed while cutting to see if that is the problem. You can adjust your speed when your running a file by holding the shift key and hitting the greater than or less then keys IE these keys < >. Listen to the sound while doing that