PyroSam

Hi everyone,

 

Sorry for being slow on the updates, I've just been really busy so work on the shell paster has slowed, but it IS moving forward!

 

I'm using an Arduino single-board microcontroller coupled with a 20x4 LCD display and keypad to control the stepper motors.  The Arduino is a very well priced choice for these type projects (it's open source so anyone can make them and they're very cheap, $20 or less from Asian vendors on eBay).

 

It's programmed in a variant of the C programming language.  I haven't programmed in a very long time, but knock wood, it's coming back!  I took a quick break from the shell paster project and bought a book, "Beginning Arduino" by Michael McRoberts.  It contains 50 projects that start very simply and build on each other to more complicated projects.  I worked through many of the projects in the book to refresh my programming and circuit building skills and have just now started on the actual shell paster code.

 

So far, so good!  I have been to control the motors without much issue.  I was starting to write some bare bones code to simply paste one particular shell as a proof of concept but then I changed gears and decided not to do that as I KNOW the concept will work and I know myself too well - I'm perpetually short of time so if I develop bare bones programs and just load them in the Arduino each time I want to paste a particular shell to get by until I have time to make a more usefull program I simply will never find the time!  Temporary things tend to turn into permanent things for me! (just being honest with myself!).

 

So, I'm working on writing a useful program - one that you would be able to simply download the code for and load into your Arduino without you needing to tweak the code for your particular setup or to modify it as you fine tune the taping profiles.  The Arduino has eeprom storage so rather than alter the code before loading it into the Arduino for such things as the drive wheel size, steps per revolution of the motors and microstepping by the drivers (if your drivers do that) you should simply be able to enter those values and store them in the eeprom from the Arduino keypad.  Shell taping profiles too should be tweakable and storable from the keypad.  In short, it should be a fully stand alone program that you can load into the Arduino and use without having to know how to program the Arduino.

 

Like I said though, I'm perpetually short of time so it's slow going (But fun!  I've really been enjoying the programming!).  That and the fact that the Arduino programming language is not object orientated, i.e. though there are some libraries to make things like reading the keypad, writing to the lcd, generating the pulses for the steppers, etc. available a lot of the code still needs every little step programmed.  Another time eater is commenting the code.  I've always been fairly good about comments but I tended to only comment where I felt it was needed (mostly just notes for myself).  Since this is for public release to an audience that's probably not experienced with computer programming I'm commenting it heavily - literally every line! (I really do want the code accessible to others as I feel innovation profits from cooperation so I want the code available and easily understandable).

 

So there you have it, the project IS moving forward!  The software is simply taking longer than the mechanical construction.  The longest journey starts with a single step though and we're already several steps into the journey!

 

Again, sorry for the lack of updates - I'll try to get better with them!

Sam

Hi Deano, thanks!

I decided to do it mostly with wood as it's just easier for most. I do have access to metal working tools but far more have access to woodworking tools, and frankly I prefer wood as it's cheap and easy to find if you screw up or re-design midstream.

I haven't woodworked for a few years and I was really surprised how junky the wood is these days! The plywood is good one side plywood but has lots of puttied over knot holes and when you cut into it it has lots of voids in the laminate. The dimensional lumber also has lots of knot holes and I had to dig to get anything even reasonably straight! I dunno if that's the result of the newer more green forced growing methods or if our local lumber yard is carrying lower quality stuff these days.

I will probably design a box to fit over the wood deck for storage. I'm thinking some drawers could probably fit under it too. The motor mounts are readily available online. 5mm thick and seem sturdy enough. Cutting the stands for the mounts on the tablesaw wasn't bad at all and with a backstop set on the miter gauge they are came out even easily.

I mounted the motor rollers 1" apart and put the arms fairly close as I'd like to do some small shells if I can for reloable cakes. If I can't I may build a small one just for that purpose. If this one can do 3-6" and maybe 8" I'll be happy! But if it could do the smaller consumer festival ball size too that'd be a real bonus.

I thought about angle iron for the upright arm mounts but the wood was easy to make and it seems sturdy enough, we'll see. Most shell pasters of this type seem to put the back arm at a higher angle and the front one at a lesser angle. I dunno why. I put mine both at a 50 degree angle. I chose 50 because if you use a CAD program and draw the various sizes of shells sitting on the rollers and then scribe a line down the edges of the shells it's almost exactly 50 degrees. I don't think the angle of the arms is a big deal, I don't really think there is a wrong angle - as long as the bearing blocks get to where they need to be things should work.

I chose not to spring load the front bearing block as it just makes it easier to build and commercial units don't all use them and they seem to work fine. We'll see if it's needed in practice, if it is it's not that hard to add it in.

They make double t-nuts but they're only an inch apart and I wanted them further apart on the arm mounts. I need to dig and see if they make a triple or quadruple t-nut I could use as it'd be nice to not have to line up the t-nuts when putting the arms on and off. These will get knobs instead of bolts eventually. If I can't find a long t-nut I may red loctite a stud in the t-nut and chase the lock nut in the knob with a tap so it's no longer a lock nut and then leave the stud long enough to stick out of the middle of the knob - then you could just twist the stud to move the t-nut to get it aligned in the slot. It's not a big issue, it's easy enough to remove and replace the arms as it is, it could just be a little easier is all so I may try to fix that.

The taping arm uses a piece of the t-slot extrusion with flat iron on the sides to allow for the taping wheel and tape guide roller. The nice part of using the flat with the extrusion is that you can adjust the overall length of the taping arm by loosening the t-nuts and sliding the flat iron arms in or out. Hopefully the t-nuts won't tend to work loose in operation, we'll see!

To make the spacers for the taping wheel so it sits dead center of the taping arm I just used some copper water pipe and cut it with a tubing cutter. That worked really well - you can make a very accurate and square cut with a tubing cutter.

That's as far as I've gotten. I need to finish up the tape rollers and figure out a spring mount. Then maybe I can get to turning some shells and working on the control software - and sort out any bugs that will invariably creep in!

Well, there it is - it's not as sexy looking as the all metal ones, but it was easy enough to build and I didn't have to run down any odd metals or have any welding or machine work done (yet anyway!).

Thoughts, comments, suggestions? (all are welcomed!)

Hi Guys,

I've been working on a frame that should be easy for about anyone to build - uses off the shelf parts and a tablesaw. Not quite done yet, but here's a pic of what it's looking like right now.

http://www60.zippysh...10762/file.html

Ned develops the taping profiles at about half of his normal taping speed - setting 3 in the software. He tapes at about 5-10 and says with a well setup profile he can move up to around setting 13. One of the software pics shows a setting of 14 for speed. I dunno what the top speed setting is but it appears running it much slower still works.

One could even run it at the desired taping speed for 80-90% of the run and then just slow down the last little bit.

We'll see once I get the frame done and get to software playing!

Hi everyone,

I got most of the parts made for my frame this weekend, I'm hoping to finish up and be able to do some assembly next weekend so maybe I can start software playing soon!

I was reading Ned's new manual the other night and one thing occurred to me and I thought I'd bounce a couple thoughts and an idea off of the group.

Ned kinda makes the dialing in of the taping algorithm look a little monotonous. Basically he's just adjusting the pole hole entry and maybe the tape width entry to get things right.

First I wondered why this was necessary as it's pretty much just geometry. The old garbage in / garbage out saying came to mind - the geometry should work if given the right starting data, so if things aren't working and need tweaking then it's probably because the starting data wasn't right. Ned seems to be making the effort to give good data though. However, if one thinks about it it makes sense - it's a mechanical system with lots of parts, angles, etc. and nothing is perfect so there's always going to be an error. To correct that error Ned is using trial and error. The pole hole entry I'm sure is just adjusting the amount of time the shell is rolled straight before the skew is made - i.e. it's just adjusting the diameter figure. Adjusting the tape width is just adjusting the angle of the skew, which is also tied directly to shell diameter.

Currently the software calculates it, the mechanics corrupt it a bit and then Ned trial and errors to dial it in. Nothing wrong with that, it obviously does work and it really only needs done once for each particular size of shell casing, but I was thinking that we may be able to help zero in on the proper figures quicker.

Basically it comes down to how many steps make a complete revolution of the shell. Shell diameters, roller diameters, ratio between them, etc. don't really matter - what matters is the final amount of steps needed for one shell revolution. If you know that then you know when to skew the tape and at what angle to skew it and everything should fall into place.

What if we installed a pen to mark the path the shell takes and then created an option in the shell configuration part of the software where we could run the motors manually. Run them slowly and watch the pen and when the shell makes one complete revolution and just as the lines meet you stop the motors -> now the steps for this particular shell in this particular frame are known. The math should now work with little, if any, tweaking.

Thoughts, comments, suggestions? Am I on the right track with the algorithm here (i.e. it all boils down to the number of steps for a complete shell revolution)?