HGDT & GGDT SUCK ARSE!

[D_Hall]

I'm not sure when I started writing HGDT/GGDT, but the first version(s) are probably close to 20 years old and it's safe to say that I've not touched the code in at least a decade; probably more like 15 years! I know it was written in VB6. Microsoft ceased support for VB6 in something like 2008 so that's probably a pretty good marker. Due to this language obsolescence, users must jump through hoops to even get it to run on a modern computer (and that's assuming you're running Windows!).

For several years it has been in the back of my mind that I should write something more accessible. I decided that I would write a spreadsheet to replace HGDT/GGDT; hopefully with a SINGLE spreadsheet. I liked the idea of a spreadsheet due to the inherent portability. Stick to basic techniques and anyone can install suitable software to load/run the sheet. Windows. IOS. Linix. It doesn't matter. If it has a keyboard there is spreadsheet software available for it!

I started to actually write something maybe a year ago? I don't know. I worked on it for a bit and got a bit disgusted with the progress and stopped. Maybe 6 months ago I posted somewhere on this board about it in an attempt to shame myself into finishing it. That didn't work. I basically came to terms with the idea that even though I wanted to revisit HGDT/GGDT, that I was unlikely to get the inspiration required to actually do so. But a couple of weeks ago I found myself writing a spreadsheet for a completely unrelated project. I was tinking and suddenly I realized that I'd written something that was very GGDT-like. Most of the math was there! I realized that writing a spreadsheet to replace/kill HGDT/GGDT might not be that difficult after all.

This past weekend I started writing.

It's almost done.

Actually, the meat of it IS done. I want to add an external ballistics calculator (EASY!) and hybrid gun fueling tool to it, but the primary sheet that takes design parameters and makes gun performance prediction is already done. It doesn't do everything that GGDT/HGDT did, but I'm not sure that matters. In practice, I found that some of the features I worked hard to add to those codes didn't actually make much difference to the final answer and/or very few people ever actually used them. Thus, I left some of those features out. Hey, money back guarantee!

I feel confident stating that it will be done and ready for release within a week or two.

There is, however, one remaining problem.... Hosting it.

As HGDT/GGDT are hosted on this site, I figure the spreadsheet could be hosted as well, but that's not my call. Thus, this open letter to PCGuy and a request (on the off chance that Spudfiles cannot host) for alternate hosting options.

Questions/comments/concerns??

[mark.f]

If it's a spreadsheet I would just see if it runs correctly on google sheets. If not just throw it on github. :p
Awesome to hear, btw. I still use both programs from time to time, honestly it's not the most difficult "retro" software to get running.

[D_Hall]

D'oh! Showing what an old codger/ludite I am. I didn't even think of google docs. I have run it on Excel and Open Office, however.

edit: Hmmm.... Just uploaded it to docs to check it out. The math bits work just fine but the formatting of the graphs is garbage....

[D_Hall]

Got the external ballistics calculator written tonight.

Hopefully, by the end of the weekend I'll have the hybrid loading tool written.

At that point, I think it will be ready for beta testing. As I hinted at previously, there are some features that I left out of the spreadsheet. Mostly it's different valve options that I don't think too many people use or take advantage of. It'll be interesting to see how many people scream about that (maybe I'm mistaken about how often certain features are used?).

[peeeto]

Thank you for providing an update! Just in time I'm starting to put together my next build and found GGDT useful last time to get an idea of barrel length considering my chamber size & pressure.

[ben25]

Thanks for the update!

[D_Hall]

Alrighty.... Anyone feel like being a beta tester?

Hopefully I do this right. I uploaded to google drive. Here's the link: drive.google.com/file/d/1jdfUvnEPLPzd9uL4uuHpn45sSfEg2UTy/view?usp=drive_link

The current format is the native format for Apache's Open Office. Running it via google drive directly (IE, conversion to google sheets) seems to screw with some of the text formating (a bit ugly, but useable) and totally dork up the graphs (unusable). I'll have to see what I can do there in time, but so far it just seems to be a google sheets issue.

In any event, I'm looking for feedback. What works for you? What doesn't? I left out a number of features from HGDT/GGDT in the belief that they either didn't make much difference or that nobody used them. If you disagree and there's something I omitted that really matters for you, say something!

Blah blah blah. You know the drill.

edit1: Damned forum software tried to embed the file in the link so I removed the h t t p s bits.... Hopefully y'all can figure it out.

edit2: And can somebody respond to this thread to confirm/deny that they were able to download the file successfully?

edit3: At this point I highly recommend downloading the file and running it on your computer locally in either Excel or Open Office and NOT running it as a google sheet.

[mobile chernobyl]

I was able to access the google drive link, download the google sheet and open it in LibreOffice Calc. I'm able to run Pneumatic and Hybrid scenarios without any strange behavior. Using Combustion I need to size up the barrel or the interior page of step calculations seems to hit a snag (#NUM!) somewhere around step / node 50.

Example would be a golfball gun - projectile (1.68in) and barrel must be 1.77in or larger. I can get around this by playing with the initial position (increasing) and then decreasing the barrel diameter closer to projectile diameter.

Otherwise works great! Thank you for porting this to a more "futureproof" tool!

[D_Hall]

Thanks for the feedback. I think I stumbled across the same glitch today. It actually appears to be a rounding error! It takes a few iterations for the algorithm to bootstrap itself and get moving. During that time, there will be a few calculations where there is zero net force acting on the projectile. Force1 - Force2 = 0. OK, but it looks like (thanks to some math that my calculator can't reproduce) the spreadsheet says Force1 - Force2 = -somethinge-19. IE, a really really tiny number, but a negative number. This forces the velocity to a really tiny negative value as well. The problem with that becomes that the error trap designed to detect that the barrel is too long and whatnot is a velocity < 0. So yeah, it thinks that the chamber is overexpanded and bad things are happening. I changed the test from <0 to <-0.01 and it seemed to go OK.

Very odd. I don't like work arounds like that but I'll be damned if I can figure out why (other than minor glitch in the CPU/rounding) the acceleration goes negative in the first place.

[mobile chernobyl]

Yea sometimes work arounds are okay in an edge case like this... I agree though - hard coding them in can cause more unexpected surprises down the road lol!

In terms of updates/on-going development (not that we expect you to keep this bad boy constantly upgraded!) - I imagine that you would use the 'live' link to the google sheet as the "latest release" version of the spreadsheet GGDT?

If so I'll download a new copy - thanks!

[D_Hall]

Ultimately, yeah, but right now don't bother (the latest/greatest isn't online). I'll update this thread when I upload something new.

After all, the last thing I want to do is make some "minor" change in a live version and blow everything up.