Your Experiences With 2010/11 PRS Standard

[gerryv]

We're seriously considering a new 5' wide PRS standard with 2.2 spindle. We really need the 5' for a product line we're planning so the existing 4'x8' PRT alpha just doesn't fit the bill. We can always upgrade to an alpha later if we find we need the added speed.

Considering the investment, what I'm really hoping for is feedback from those of you who have purchased one of the newest Standard PRS machines ((with the new, silver controller boxes and the change to OM/Vexta stepper drivers)) to get your impressions. Spindle or router model doesn't matter.

In particular, I'm wondering if the recurring comm. errors that a few users experienced with earlier versions have gone away with the introduction of these new boxes and the OM/Vexta stepper drivers.

Also, I've been impressed with the smoothness of arc's and shapes with the 3.6:1 motors on my Standard Buddy 32 with the Gecko drivers. How are you finding these newer versions in this regard, including when doing 3D work?

Please feel free to respond offline to my email gvowles(no space)@(no space)mac.com

[michael_schwartz]

My PRS Standard is a little over a year old.

After replacing the defective keyboard and mouse I had been using I have not had any com errors occur under normal circumstances while cutting a file.

Furthermore I have been lucky in the regard I have not had a com error occur in a way that affected the project I was cutting.


I have also had a few which I attribute to the connection, disconnection of my USB thumb drive.

I have had a few unexplained errors while the bot is sitting idle. In those situations I have been able to restart without loosing position. They still happen from time to time, and my feeling is that they are due to a stability issue with the control PC. The older dell I use to run the bot is on the short list of things to replace.

I can't comment on how my machine compares to an alpha since I have never seen one in person. I can however say that the standard has met my needs quite well . I mostly cut solid wood, and less frequently sheet goods.

With really careful setup including roughing, and finishing tool paths I have been able to achieve surface finish on par with that left by the byrd/shelix head installed on my PM60 jointer. Hold down, Bit selection, Tool Path Setup, and accounting for any run out, bit/machine flex are really the ultimate factor that determines cut quality.

I have never cut a circle and checked it with a trammel. I have not found it necessary to do so yet. As far as the eye can tell the arcs, and curved parts I have cut are quite smooth and appear true.

As far as cutting 3D I am quite pleased with the results I have achieved. If parts are to be viewed at a distance you could get away with little or even no sanding.

[gerryv]

Thanks kindly for all the good info Michael, it sounds encouraging. I suspect that a lot of these comm errors likely have something to do with the PC and perhaps shielding. Heck, in the past few months that I've finally gotten around to spending time with my 2006 PRT Alpha and my PRS Buddy, I've not run into these issues yet and I've not even grounded either machine yet :eek: Hey, maybe that's the secret, heh, heh.

I'm kind of surprised actually that you are the only one to respond about this. I'd have thought that there would be quite a number of owners of these newest systems but maybe not or perhaps the new owners just don't contribute in the same way as the longer term guys have supported the forum.

[Brady Watson]

The RBK Oriental-powered Standard machines are more powerful than the previous Gecko-based models. First, the new 3.6:1 motors have a higher amp rating, which translates to higher torque. Second, the RBK driver supplies more current to the motor (not that a Gecko couldn't), and also adds 'software shifting' which moves the motor from microstepping to full stepping at higher speeds, allowing for more rapid positioning. The Gecko also does this, (via morphing) but the Oriental seems to do it better, with higher jog speeds being the yardstick.

I was very surprised at how difficult it was to knock an axis out of whack by overpowering it by hand (very difficult!) compared to an earlier 4G model. This is a direct result of higher amp motor/driver combination. The new PRS Standards are very nice machines, and are on par with an Alpha in many ways, except for maybe high speed torque.

-B

[wberminio]

Gerry

I have an "older"PRS Standard , one of the first-With the 4 g board.
Haven't had a loss comm issue in 3 years.
I also have a Shopbot drill head installed (which is not recommended now)-but works for me.

Great solid machine.
Looking to upgrade to an Alpha but can't justify it ;).
Looks like the upgrade Brady talks about maybe worth it.

Could use a bit more torque.

[michael_schwartz]

As always Brady hit the nail on the head with technical details.

I may upgrade to an Alpha someday but for the jobs I cut, I typically use slower feed rates. Jog speeds can add up, but for the cutting I do they are not a big deal either. I almost always have the extra time to let the bot run a bit longer anyway. I have only had problems with lost steps when trying to cut way to fast or letting the dust foot bind up on stuff.

Planned upgrades will be a vac table, and then a spindle, and maybe even an indexer/additional software before I consider going to an alpha.

At least if you do decide to upgrade in the future selling the standard control box/motors will be quite easy.

[richards]

(This post is off-thread and does not address the comm errors, but it does address some options 'botters have if they already own the 4G upgrade.)

For those who already have a 4G, there are some options that will make that 4G outperform an Alpha. The secret is matching the stepper drivers to stepper motors and power supplies that let everything work together. The 4G upgrade should have included new motors instead of re-using the 4-wire, 1A, 30.8mH motors that many 'botters already had. That would have cost an additional $1,000 per machine, but it would have solved many of the problems that the newest control box is finally addressing.

The G203v stepper controller used in many of the 4G upgrades, can handle up to 7A motors. It is best used with motors having 6mH or less inductance. It is limited to 80VDC. Oriental Motor has several stepper motors that fit those specs. I like the PK296-F4.5 and the PK299-F4.5 motors. The 299 motor, when wired bipolar parallel develops 880 oz*in holding torque. Tie that to a 3:1 belt-drive gearbox and you would have 2X the torque of the PRS-Alpha motors. Used with 1.25" pitch diameter pinion gears, that 3:1 reduction would have a resolution of 0.00065" per step. A 45VDC power supply could be used for optimum speed without creating excessive heat. At 25,000 steps per second, that motor would be jogging at 16-ips. As far as I understand, the controller's ability to produce step pulses is the limiting factor. I've personally run that motor at over 100,000 pulses per second with an obsolete Gecko G100 controller, which spins that motor at 65-ips!

The RBK matches a motor to a suitable controller. It can use a power supply up to 75VDC. It has more options than the Geckodrive stepper drivers, but it won't do a better job than a properly tuned Gecko system.

Anyone buying a new machine will be very well served with either the PRS-Standard controller or the PRS-Alpha controller. Those who already have the 4G might consider replacing their motors, the power supply and mounting the Gecko stepper drivers on a good heatsink before they replace their entire controller. For the price of four motors and a little elbow grease, they'll have a top-notch stepper system.

[wberminio]

Micheal
Thank You for information.
For those of us that are not as technically advance-
Would it make sense to just buy the new RBK as an upgrade from Shopbot?
How would someone like me fabricate 3:1 belt-drive gearbox?
I wouldn't know where to start.
I would love to get the results you take about.

Thanks again

[br928]

Mike,

Did you post your plans for a belt reducer in the past? If so, maybe you can post them again or a link to them. Anyone that has a Bot can easily build these with off the shelf parts. I found several designs on another forum. I plan on building some for a friend who is upgrading a 2000 vintage PRT.

[bleeth]

I've been thinking about this as an option for the next stage of upgrading my PRT. I found this supplier for gears (scroll down for the suggested 3:1 kit):
http://motiontek.ca/pulley.html

Mcmaster also carries pulleys and belts.
Mike had a computer crash that wiped out his original design. I've been looking for some specific designs (Hate to re-invent the wheel) but so far no luck. Search engines don't always work the way you want.
Do you have links to what you found available Stan?

Mike did send me his parts list:

1 ea. pinion gear (25-tooth or 30-tooth)
1 ea. 20 tooth XL-pulley
1 ea. 60 tooth XL-pulley
1 ea. 150-tooth XL belt, 3/8-inch or 1/2-inch wide
1 ea. 1/2-inch drive shaft, length depends on design
2 ea. shaft collars for 1/2-inch shaft
2 ea. ball bearings to fit 1/2-inch drive shaft
2 ea. bearing blocks (not needed if 1/2-inch thick DelRin is used for motor/mounting plates
2 ea. rubber O-rings that sit between the collars and bearing to eliminate binding
1 ea. motor mount plate (user designed)
1 ea. mounting plate
4 ea. spacers to hold the motor mount and mounting plate apart

Depending on the material used, the cost for each axis is about $100 to $150.

So the object for me is to design it so it will work within the physical layout of a PRS. Also nice to have the gearbox design so it works on all 3 motors (don't need it on the Z).
Big question in my somewhat limited mechanical mind: With required movement in the pinion shaft adjustment to ensure the right tightness against the rack does that mean that the design has to have that move in an arc from the motor shaft or is some kind of an adjustable idler arm required to keep the belt tight?

[gerryv]

Dave,

I'm about two hours away from Motiontek so, if you'd like, I could go in to "eyeball" their stuff in terms of basic stuff like quality of machining and concentricity.

I'm interested in doing this myself so we might even be able to lower setup costs if we could find a good machine shop to build them. I'm also wondering about the benefit of a geared motor on the Z to reduce visible "steps" when doing 3D.

Anyone else thinking the same?

[bleeth]

Gerry:

Taking this to another thread to stop the "hijacking":

http://www.talkshopbot.com/forum/showthread.php?p=108545#post108545