Archive through October 04, 2000

[phil]

Can anyone describe how they have implemented limit switches to sense home and overtravel?

[birdsofplay]

I just drilled and tapped the SB side rails
for the hole pattern on a coupla heavy duty microswitches.

I grounded the frame to the I/O board
and just run one wire to the switch.
the other side of the switch to the frame

I got a new dig cam ... want a PIC ?

[phil]

Thanks for the information. What I was wondering was the following: Install four switches all hooked in series. One switch for each of:
X-zero, Y-zero, X-overtravel, Y-overtravel.
Any switch that gets activated would send a signal to the box, and depending on the state of the table (was X moving positive etc..) the program would take appropriate action. I'm thinking that one program could look after the original homing action and the overtravel supervisory function but haven't quite got it figured out yet.

[birdsofplay]

Um ... ?
Why series them ?
SB has several inputs available.
Use one each for X, Y and Z .

I think you can program a stop based on any
SWitch input being tripped.

Take a look at ted's probing program and the
Z Zero program for some pointers.

[birdsofplay]

I should have said Parallel is what you want
for overtravel. Just run all 4 switches to one
input port and the other side of each switch to ground. All switches will be NORMALY OPEN
If any one of them closes from overtravel
then the program would STOP the ALL motors
ie. " MO "

That leaves 3 ports for zeroing or whatever.
Of course you'd have to use seperate switches OR
back off of each zeroed axis before zeroing the next. Yeah, THAT would work :-)

ie. Zero X then JX,1 then zero Y then JY,1 and then do Z .. then move back to zero
on all :-)

[birdsofplay]

I have placed dig cam pix of some mods
and LIMIT SWITCH installs that I've done on my pages.
Including the inside of the SB box for connection
details. Please Excuse poorly lit grainy shot.

Mods are purely my own and not intended for
production ( at least not by me ).
I'm not promoting this method, just sharing
another way to do things. I did NOT do the cad
drawings to specs. I just scribed and drilled
the plates from parts in hand.
So dont ask for blue prints.

Nope, I dont have the encoders hooked back up yet either. Maybe soon .. maye not at all, I havent decided.
Note that bird toys dont require much accuracy :-)

Oh yeah ... where are they ?

http://www.birdsofplay.com/sbpix/sbmod.htm

[robin]

Bob, you are too modest about your modifications. Crappy, cheezy, and lousy they aren't! A few questions:
1. Are those the original motors?
2. Where did you source your reduction pulleys (and, if you are using the original motors, what ratio did you use)?
3. What voltage/current are you driving it with (I seem to remember you upgraded your power)?
4. Are you happy with your setup?
Thanks again for the pictures and inspiration.

[dthorpe@gte.net]

Yeah Bob,
you're the man, tell us hows it done.

[birdsofplay]

Now come Onnn ! I aint "da man" , really ! :-(

Dennis Thorpe is the guy who got me up off my duff and out of a state of procrastination. He actually did this kind of mod (to my knowledge) FIRST !

Dennis and I have been getting stuff from several sources.
Stock Drive Parts and Motion Industries ( formerly Berry Bearing )
Dennis has a locel rep that even comes out to his locale and evals his intentions and makes suggestions. Good help and lots of catalogs too :-)
Motion Ind has Sprockets and .25 chain stuff as well as other stuff.

MOST of my stuff was actually from salvage of some
old computer backup library mechanisms.
Come on guys ... Get Creative !!!
All my bearings came from that "tear down" .

All my drive shafts were hardened stuff at first but I had probs with keeping the sprockets and drive gears tight so I've swapped out for SS shafts that I can drill holes for set screws to go into !
The idler sprockets still have real hard shafts but they dont have a need to be securly set screwed.
If my drives loosen up again I'm Pinning everything.

I have NO mill or exacting maching or grinding facilities. So this is a total HACK !

I have those belts VERY tight and Art Ross has
informed me that HIS engraving machine uses chain for the Motor to drive shaft drive as well.

Total chain may be a better way to go for reliability.
They "might" be slightly less accurate for those
who need the "best" precision.
But for "Bird Toys" I'm pretty happy.
And It's not doing bad with engravings either.

Also my chain is HARD mounted at both ends.
It's been relayed to me that a "tensioned"
mounting at one end of each would be better.

I have always figured that SB was a terrific
starting point for the "hacker" in me. They provided great SW and drivers and "get go" help.
I'll always have a soft spot for SB and good words about them ( well most of the time :-)

Now to do anything else ... well, it's up to
the end user to "invent" .

Dennis can tell you guys about his latest gantry
creation and dual head machine.
Those Wisecarver wheels and V track are yet another way to make things smooth and accurate.

I be glad to "web" the pix for him if he wants.
I already have some of his pix.

If you guys have some different ideas or mechanics
to show around and need the pix "put up" , just
let me know. I have lots of web space.

[llarson@softdisk.com]

I'd sure like to hear (and see) more about those Wisecarver wheels and V track.

Thanks

[birdsofplay]

Well, if you look closely at the Thrustbox picture
on the ShopBot pages, you will spy a wierd looking wheel in the background. It looks like a narrow pair of wheels mounted together, but it's only one wheel.

I have heard that SB is/was using/offering these as substitutes for the originals. I dont know what they are shipping at this time.
Mined you, I bought my SB over 15 months ago.

There are several "grades" of these style wheels.
the better has TWO bearings and are very rigid.
ie ... no wobble. These are $16 to $20+ depending on your resourcfullness or willingness to dig.

Also you can obtain "V" track for them to ride on, but bring your wallet. It's about as bad as buying
your own rack and pinion supplies.

Dennis Thorp has obtained a catalog with all the technical PooP re these parts - and prices !
Or lookup Bishop Wisecarver in your favorite TomCats.

[Ted Hall, ShopBot]

FYI ... yes, ShopBots now come with the Bishop-Wisecarver bearings ... they have for a year or so, I think ... however, we still like the way they ride the edge of the strut. Most of the probems we had with this arrangement were due to the looseness of the original patio door wheels and their relatively rapid wear. The B-W bearings completely eliminate these problems and give a smooth, friction free ride. Going from $1 to $15 a bearing was a little hard on our philosophy here though, and unfortunately, contributes to a more expensive tool ... BUT the robustness is worth it.

ON THE LIMIT SWITCH. You may have noticed that the latest beta software (beta8) has two automatic Input Switch features. Input Switch #3 will automatically act as limit switch if a file is running or if a single command is being executed. You can turn this feature on or off with the [VN; 'V'alue i'N'put Switch] command. The command shows up on the pull down menu, but it not yet documented in the Command Referece, on-line help. This switch can be made to work well with the switches described in the posts above. All you have to do is bring the switch input line to ground. So just wire in parallel as many switches you need. You can take just a single wire to each switch by grounding one of the switch's contacts (assuming your tool is properly grounded). When the limit switch line is trigered, the software will pause for instructions and alert you to hitting the limit. Note that if you were writing a file to use the limit switch to zero or calibrate your tool, you would turn this automatic function off so that you could define the specific zeroing or calibration function for the switch.

A RELATED SWITCH. In the new software, the Input Switch #4 is now a dedicated panic switch line. Activating this switch will have the same effect as as hitting the space -panic- bar.

[birdsofplay]

Thanks Ted. I wondered why my X and Y zeroing
programs acted funny on the new SW.

So, is the panic line disableable too ?
and then useable for other stuff ?

Just askin ... no specific plans for it.

Thanks

[pkleinjan@u-r-online.com]

instead of running the bishop wisecarver bearings on the edge of the strut material, i bolted a length of 1 1/2 x 1/4 cold rolled flat bar to the top and run the edge of this. bolt thru the strut every 12". the holddowns will still fit. super smooth action this way at minimal cost.

[Ted Hall, ShopBot]

Hi Bob,

We decided that if there was a Panic Line, it should not be possible to have it 'accidentally' or otherwise over-ridden in the software. Somebody might have a file that ran and unknown to someone else working the tool, might disable the panic line ... this would thus create a safety problem.

Therefore, Input #4 is now Panic and can not be disabled.

What do you think ... ?

[birdsofplay]

I agree.

Safer is better.

I was just looking for options, thats all :-)

Safety is NOT an option !

You did good, as always

[Mark@Walkerframes.freeserve.co.uk]

hi bob, its great to here you mention the hardened rails for the bw bearings to run on. i have just finished a table with rails made from 50mm x 50mm box section with 20mm x 20mm angle laid on 2 edges so that it offers a 90' angle for the bearings to run on. i have mig welded these @ 6" spots to retain full straightness. it provides vertical and lateral positioning and bcause i have used a complete box section i can use any of the underside of the completed rail as a hold down strip for sealed bearings to run on. the result is a very smooth axis movement which should wear only after many hours of constant use.
Mark@Walkerframes.freeserve.co.uk (mailto:Mark@Walkerframes.freeserve.co.uk)

[RJGUINNDSN@aol.com]

Having a problem using mechanical limit switches (table limits) & electronic proximity swiches (zero X&Y) when all are conected to IMP#3.I am constantly getting limit switch error & mechanical switces are disabled. The problem is resolved when I disconnect the electronic sensors.Wondered if the prox. switches could be connected to IMP#1 or #2 which will still allow limiting of overtravel by mechanical switches while zeroing X&Y with the electronic sensors? I purchased the sensors from SB. Any ideas will be greatly appreciated.

[garbob]

I am just finishing up the wiring and table on my new PRT96 and have used an idea that Bill Young mentioned which is similar to the S_zzero.sbp program using a metal plate hooked to input switch 1 or 2.

I mounted a grounded target for setting zero on x and y and glued two blocks of wood with a bolt through each that is hooked to the same input switch for zeroing z. This works fine. I use the same coordinates for the table base and for working coordinates, usually. That way if the two don't agree I know something has slipped and I can just reset x and y by running the program. I use the software limit checks and have not had a problem exceeding them.

One other problem that I have with some files created by customers or software is that sometimes the shopbot file exceeds the limits of the table. It's hard to see this so my partner has written a program to import the file and check that nothing is outside of the table. I have put this up on our web site for free download at http://www.sugeri.com. Try it out.

[birdsofplay]

The Preview mode in Shopbot should also tell you this.

If it's outside and you still want to see it
then set teh X and Y scale to something
less than 1.

I too have written a Visual Basic 6.0 program to
verify SB files but at present it only works
on line segments. I'm working on adding arcs
interpretation next.