Always a Newer and Better SHOPBOT!!!

[roney]

You guys at Shopbot must never sleep. It seems that you are in a constant upgrade mode, which is great for US. My 'bot' is new as of 01-12-01, having what I guess at the time was the newest pinion gears (20 teeth), and just today somebody e-mailed me and told me that they just counted their pinion gears and that they have 30 teeth, WOW!!!...or at least I guess it's a wow...what difference will 30 teeth make over a bot with 20 teeth? Are the new and improved pinions available to others?
This is my third post today, am I addicted to this forum or what?

[mike]

my bot came with 17 teeth in the pinions ( not even listed in the manual ).---Took me a while to figure out the vu settings . ----I was cutting out some brass letter today and the edges were a bit bumpy from vibration . If I changed to 30 tooth bits would I get better results ?? ---If so were can I get them and how much ??

[djhazeleger@mindspring.com]

If the pinion gears are up to 30 teeth the resolution for the machine would decrease 50%. If they are now shipping 30 tooth sprockets I would think they would have to increase the microsteps. In Teds post he mentioned a commercial driver they are now using, so that may be the case. Anyone have a new machine to shed some light?
Dirk

[rbsears]

I recieved my new machine the 2nd of March, finally got it together and with a few minor problems with windows (finally ended up using DOS) my Shopbot runs like a top. It has the 30 tooth pinions.
Richard

[birdsofplay]

Orietal Motors can be had with several gear ratios
so speculating re power or whatever may be
a bit premature IMHO.

I was thinking that possibly SB has gotten some
motors with different ratios due to supply issues
and they simply made the "adjustment" via various pinion sizes.
The SB gear engagment design is NICE that way.

[djhazeleger@mindspring.com]

On the first new machines Shopbot went to direct drive and eliminated the gear reducer. The pinion gear is directly mounted on the shaft of the motor. Microstepping has taken the place of the gear reducer. If they are using 30 tooth pinion on the newest machines then something else has got to have changed. To get the published resolution they have either went back to gearmotors or increased the count of microsteps per step. What's changed...Anybody?
Dirk

[rbsears]

I recieved my new Shopbot March 2 and here is a paper that was with my new machine:
About Your New Shopbot....
Hello New Shopbotter!
This is an insert to your Manual and documentation that contains important information about your tool.
Your tool has been shipped with gearhead stepper motors. The addition of the gearbox to the stepper motorsprovides improved power, resolution, and smoothness of cutting to your Shopbot PRT. We have changed to this (more expensive) power system to provide cutting quality beyond that provided by microstepping alone. We believe that you will find that this combination of motor, gearing, and electronic drive system provides the performance you need for your cutting and machining operations. The following sections describe the installation of the motors and provide the correct Unit Values for your tool to insure that the software is fully calibrated with this drive system.

There is a bit more about installation but I doubt anybody would be interested in the rest of it. I don't know if this answers any questions but I tried.
Richard

[alton]

The number of teeth on a spur gear(the one on the
motor) has no effect on the gear ratio.
Smoothness maybe, but not ratio.
The ratio is determined by diameter and circumference.
Larger gear=more speed, less torque and accuracy.
Smaller gear=less speed, more torque and accuracy.

Think of a ten speed bicycle. Smaller sprocket=more power less speed. Larger sprocket=less power more speed. The same applies to rack and pinion.

Alton

[Gerald D]

I get the impression that there are continuous changes from ShopBot in the motor drives, and a heck of a lot of confusion as to who has got what and why. A basic understanding of motor/gear transmission would maybe help to shed some light.

The number of teeth on a pinion is a meaningless parameter if taken in isolation. As an example, a 15 tooth pinion riding on a rack with teeth spaced at 1/8" intervals, will have exactly the same performance as a 30 tooth pinion riding on a rack with teeth spaced 1/16" apart. In these two cases you can see that the diameter of the pinions will be the same.

The main parameter to look for is the number of revolutions that the motor must turn to produce one inch of linear travel of the carriage. (We could call this the overall transmission ratio OTR). For a given motor, if the number of revolutions (steps) are increased, then the speed drops but the thrust force increases - equivalent to selecting "low" gear in a motor car (automobiles for the Americans). Alternatively, if you go to "top gear" (or Drive), the speed increases but the thrust force drops.

We have seen rack & pinion SB's with the pinions directly mounted to the electrical motors and we have also seen an intermediate gearbox between the motor and the pinion. A direct drive 15 tooth pinion with 1/8" teeth will have the same OTR as a system where there is 2:1 reduction gearbox driving a 30 tooth 1/8" pinion.

Generally one would prefer a direct drive system because of less things to go wrong and less places for backlash to develop (also lower cost). However, the pinion gear then tends to get a little "coarse" because it is small and has few teeth in engagement. Making the tooth size smaller (finer) is one way to go, but then the rack gets more susceptible to dirt and the teeth get weaker.

There is a very fine balancing act to achieve the right OTR in terms of numbers of teeth, numbers of gear wheels and size of gear teeth (pitch). On top of this is the dilemna that all the Shopbotters have different expectations and are doing different types of work with the same machine. It would be the same as General Motors producing one vehicle only for a market that wants low-geared towing vehicles as well as high-geared oval racers.

[GD]

Alton, sorry for the overlap - it took me more than 23 minutes to type this thing above.

[birdsofplay]

I have looked at rack offerings in several catalogs. It seems that the finer the tooth pitch
the narrower the rack and gear are.

Finer and smaller gears are narrower and/or weaker.

This makes some sense but it also means weaker since there is less steel to steel engagement.
Rack and gears are not cheap so doubling up on rack to achieve strength is costly.
See MSC, McMaster/Carr or Reid catalogs for pricing.

Also the output SHAFT on the motor or gear box has
a fairly large diameter ( 3/8" to 1/2") on the bigger motors which limits the minimum size of pinion selections.
Surely one could devise an adapter to achieve smaller output shaft diameter to accept smaller
pinion selections, but now were using less robust shafting and adding parts and mounting operations.
Or the output shafts could be milled down to smaller diamater.
Again, more cost and "specialized" machinery.

All designs are a compromise.

Generally maximum Jog speed and Power are INVERSLY related to positional resolution.
At least with stepper motor driven systems.

I guess my question is;
Why are we questioning the SB design in the first place ?

Unless we are willing to go to the expense of a
SERVO driven system then we're kinda stuck with the constraints of steper design.

SB is merely attempting ot optimize within the avialable and affordable constraints.

Now IF SB had Step and Direction output THEN one could
purchase a Gecko Stepper to Servo driver board and
purchase servos with encoders. One set for each motor !
The net result being a big jump in overal price.
I suspect at least $1000 increase.

It boils down to the old addage ...
Good Fast or Cheap ... pick any TWO !

[ryan@trueride.com]

What is the vu xy setting for 30 tooth pinion gears? My machine is making a clunk every foot or so and vibrates slightly during operation. Perfection is a must for my product and I want the smoothest running shopbot I can get. Seems to me that the 30 tooth gear is too large for the rack. I would consider buying standard 20 tooth gears to achieve a liquid smooth shopbot.
Any help is appreciated.

[rbsears]

Ryan, mine did the same thing in windows(I guess my processor wasn't big enough so I went to DOS and it cured it.
Richard

[roney]

Bob,
Since I started this thread, I would like to explain that when I heard of a possible improvement to the shopbot, I simply wanted to know the reasoning behind it. I was not questioning the genius' at SBHQ. I wanted to know if it was an upgrade worth upgrading to. That said, riddle ne this; When is an upgrade not an upgrade worth mentioning?
SB just e-mailed me answering a question I had e-mailed to them Thursday, asking when and if Vector 9 would be available. They wrote me that it's available now for $175.00. So my question is, isn't there a forum topic that SB uses for anouncements? If so, then I must have missed it. If not, then why not make an anouncement?
jrc

[birdsofplay]

Rodney,

A very good point indeed.
I always wondered the same myself.

Posibly SB deems all these minor incremental improvments to be too small to mention, one at a time, and then looses track of mentioning them at all.

This Forum is a wonderfull tool provided by SB and I do appreciate it.

But since the Forum has taken the place of the circulated Newsletter, of years past, then I had assumed that the FORUM would also be the place to find all the ANNOUNCMENTS, as you pointed out.
So much for assumptions, eh ? sigh ...

SB is easy to forgive, however, since I'm sure they are simply overwhelmed by demand and growing pains.

[Ted Hall, ShopBot Tools]

Gee Fellows ... this one got pretty far along before I noticed ... so forgive me if I don't get everything addressed ... but here goes.

On announcements: Yes ... our plan has been to make major announcements in that section of the forum. We have not been using it as well as we should ... and I apologize. We'll do better. On the Vector upgrade thing ... we just haven't had time to get the info up ... and there has been a lot of confusion in our getting the upgrade material. It will happen shortly, and we'll make sure you all know about it and post it here.

OK ... now to the gears. We plead guilty to continually fussing with the gears. Over the last few years, we have gone up and down a number of pinion sizes in search of that perfect ratio where we get reasonable speed without giving up power and precision. Nonetheless, most everybody is in the same ball park ... some a little higher, some lower. That's what Unit Values are for. Indeed, I hope you've always been clear that these are off the shelf Boston Gear pinions (20pitch;14.5deg pressure angle). No Magic. For anyone who wants to explore gear ratios ... it's easy to do. ShopBotters with specialty applications have done this to quite a degree. We have a couple tools cutting foam fast with 36 tooth pinions, and others doing high resolution work with small pinions (though below 16 teeth I do not believe they run smooth enough).

Unfortunately, in the last 6 months the story gets much more complex. When we went to the PRT tool, we switched to new stepper drivers (microsteppers from Intelligent Motion Systems IMS). Microstepping allowed us to use straight drive motors and (as mentioned above by someone) get resolution electronically. This had the added avantage of simplifying the drive system (less noise, backlash, etc...). Through January 2001, we shipped tools with these drivers and straight drive motors. However, during this 6 month period, IMS has not been able to reliably supply the drivers in the quantities that we needed. We struggled with this supply problem for many months and decided that we could just not live this way. During December and January we worked out a new control board using drivers of our own design that feature components with multiple sources. (Those with IMS-driver-control boards should not worry, we have put a large number on these drivers in stock on the shelves and expect to have any spares that may be needed in the future.)

Since we were redesigning the control system from scratch, we decided on an approach that still used microstepping, but also fell back on achieving some resolution from gearing too. This seemed to offer the best range of speed, power, and resolution tradeoffs and the most flexibility. So ... in February we started shipping tools with gearhead motors (initially with IMS-driver control boards). Tools shipped in March also had ShopBot-driver control boards.

Over the last several years, we have been very impressed with the Oriental/Vexta motors we've used, both the straight drive motors and the gearhead motors. Thus we are quite comfortable with this new arrangement. It's a little more expensive than we would like ... but the flexibility makes up for quite a bit.

With the gearhead motors, we have been shipping 30 tooth pinions (with 7.2 reduction gearheads). To further the confusion, we expect to eventually shift to 3.6 reduction and 25 tooth pinions (a little more fine tuning). FYI, I am working on some graphs which will lay out some of the benefits and tradeoffs in gearing choices. Stay tuned ...

The control boxes with the new ShopBot drivers can be configured to full, 1/2(torque compensated), 1/4 or 1/8 micro-stepping as appropriate for the gearing situation.

With every tool, we now send a table with gearing and Unit Value information as well as recommended speed ranges for cutting and jogging ... and we attach a copy to the Quick Reference Sheet. But you probably do want to keep in mind, that there is going to be variation in the gearing of ShopBots. In the big view, these differences probably only influence the various performance factors by +/-20% (except where really large changes are made, e.g. the 36 tooth gears).

A smaller issue raised above concerned "step & direction" drivers. Actually, since the PRT series started, all the Control systems are step and direction. From a current control box, one can directly access the step and direction signals (they are marked on the PC board). If you have an older ShopBot and you have an interest in step and direction, the control box software that is packaged with the version 221 software (for PRTs) contains a control box loader (LOAD40C.EXE) that will make your controller produce step and direction signals, which would allow you to disconnect the ShopBot drivers and hook up step and direction drivers. I'll try and get the a key posted to the output lines for this scheme. I would not recommend mucking with it for the faint of heart ...

Hope I've touched on most of the issues here ... we'll try and do better on Announcements.

[sheldon@dingwallguitars.com]

Ryan,

From your description, it sounds like I was having the same problem with my machine. I determined that it wasn't a mechanical problem because the clunking wasn't happening in exactly the same location every time. After much time spent trouble shooting, I changed PCs and the problem went away. The steppers run very smooth now. I don't know if the incompatibility was driver related or hardware related (I was using a Compaq with a non Intel CPU).

Ted, I would be very interested in a Servo upgrade at some point in the future.

[roney]

Ted,
Thanks for the clear-up.
jrc

[Michael Garrison Stuber]

This of course leads to the inevitable question. I just ordered my shopbot for a second week of April delivery. What am I going to get? Something good I hope!

[bitbreaker]

Servo conversion:


First:
Grab The ShopBot MicroStep version SW
Set it up for Step and Dir output.
Ted will be posting the info soon re ports

Then goto ...

http://www.seanet.com/~dmauch/

to buy servo motors,
excerpt follows ...

NEW ! Servo motors with optical encoders.These are new ballbearing, DC Brush type motors that have an optical 200 CPR HP optical encoder (800 Counts in quadrature) The motor shaft is .3145 Dia X 3/4" L Motor is a 24VDC brush type with quick disconnect terminals. Approximate peak torque is 420 oz in. Body diameter is 2.25 and 5.25" long. It runs our Mill Drill at 180 IPM. Great for mill/drills or 3/1 machines Nema 34 adapter plate are also availble at additonal charge.Price is $110 ea plus S/h. I f you need a differenent encoder wheel add $20 per motor and specify the number of CPR encoder you need. For encoders with 540/1000/1024 CPR add $30 additional per motor

NEXT:
go to this URL and get their
Step and Dir to Servo drivers ...

http://www.geckodrive.com/

excerpt follows ...
This drive takes a DC brush motor with a quadrature encoder and allows you to servo control it with a step and direction signal. This unit is ideal for retrofits where stepper motion needs to be replaced with a servo motor. AVAILABLE NOW FOR ONLY $99!

FINALLY:
Engineer all those pieces into a
nice CLOSED LOOP servo driven system.

Caution:
Experimenters only may apply for this job :-)

[bwclark@centurytel.net]

Bitbreaker,

Couple of things....

First, the Gecko G340 would be a better choice for the servo drive. First since the SB is limited in how fast it can output steps per second the G340 with built-in pulse multiplier would work MUCH better. It is also only $30 more than the standard G320.

BTW, I can vouch for the DC servo drives. They ROCK! I have used them, but not on a ShopBot.

Second, while Dan Mauch's motors are very nice, you can often do a lot better by checking on such places as Ebay (use such search keys as "servo encoder", "dc encoder", "encoder motor"--these will turn up a LOT of good hits), local surplus houses (Marlin P. Jones, Electronic Goldmine, ect), or even your junk box/drawer--a lot of old printers and vinyl machines contain dc servos with quadrature encoders.

Last thing, the encoder that provides feedback is also the "weak" link, as they are VERY susceptable to contamination. Most quadrature encoders are HP, while very good, rely on the motor manufacturer to seal it from contamination. Well, most of the motors that I have seen/own would not seal out the kind of dust my Shopbot makes. So, in this aspect, steppers are better!

Just some thoughts...

Bruce Clark
bwclark@centurytel.net (mailto:bwclark@centurytel.net)

[danhamm@abccom.bc.ca]

It seems awfully quite on the forum!
I have put a few pics. on my website "Bruce"
some thoughts on them? maybe we can get some action going for the weekend..

http://www.burningimpressions.ca/fixit

[bruce_clark]

Don,

Just some quick calculations...

To retrofit a 4 x 8 Shopbot with the LM rail with
built in rack (at the price you stated) would be
$7500 canadian. Kinda expensive, but otherwise
that is very kool.

Check on places like Ebay for rails and guides for
surpluse motion control parts. You could get your
whole machine "upgraded" for a lot less than just
the the price of the rails alone.

Bruce Clark

[danhamm]

I have no intention of upgrading my bot..other than the "Z" axis its the pr series..
My math is a little different than yours,
Rack and rail 312.00 x 5
LM stabilty rail 184.00 x 5
12 pads x 87.00
24in. "Z" axis screw.412.00
5ft 4x12 extruded box aluminum "X"axis"new"
2-2x12 channel aluminum vertical rise for"X" azis
don,t know prices on this..
vexta pk296 300.00 ?for "Z" axis
=$4236.00 + taxes
with agood base under it, would be as strong and
as accurate as the 1.2K machines..
I spent a day as a guest in the University of the north. they have 2 cnc's,I came home more impressed with the shopbot's simplicity.

Dan Hammerstron

[olivier]

Hello there,
Speaking about upgrading, I am considering going for the new shopbot with ball bearings and welded frame. Is there anybody out there who has upgraded from the carriage wheels and bolted frame ? Is there a real difference ?
Also, I read on a posting earlier, that the motor where being offered with direct drive, (no gearbox would mean no backslash and maybe a very different noise) , but that later on, because of supply problem we are back with the gearboxes . What is the situation now exactly as far as the backslash is concerned ?
And what about the noise? Is it still this kind of harmonic cranking cum vibration ? (I am about to buy a very silent Perske Engine that should enable me to hear it )
Also I read on the shopbot web site that the max cutting speed with force is 100"/min ie 1,66"/sec.
I personnally regularly cut at more than 2"/sec without problem. Is there a trade-off of speed for precision in the new tool ?
Comments from Shopbot would be welcome.
I think the three areas improved : rigidity of the frame, get rid of the wheels, and the backslach of the motor are the only limits I see in my tool today. That would make the new shopbot close to the perfect tool for the price then...
Olivier

[cmrtom]

The new photo of the shopbot on the website has a very nice looking router..........what is it, how much is it, and where can you get them?

[bwclark@centurytel.net]

Mr. Foster,

That is a Persky router. Not sure the exact HP but looks like a 2 or 3 hp unit. They suppose to be quieter and more heavy duty than most other off the shelf routers, but the downside is that they start about $2K, require 220V/3 phase power (depends on model and if you get a variable frequency drive unit--which electronically controls RPMs).

If you can live with the noise, it is still hard to beat a Porter-Cable 3.25 Hp router. Inexpensive to buy, service, and you can buy a new one when the old one gives up the ghost at most Home Labyrinth stores.

Bruce Clark
bwclark@centurytel.net (mailto:bwclark@centurytel.net)

[olivier]

Hello there,

I am planning to set up a Perske 5,5 HP on my bot, Weights 16 Kg...
Will the z axis handle this weight ? Should I modify the compensation with the strings ?
Any experience welcome.

Olivier.