Homebrewing an XYZ CNC Router

The MOD thought it could write the software for Chinooks, was advised by Boeing that it would be a difficult task, ignored that advice and cost us all millions. The software was never written and the Chinooks are still not in service!

...but they care about such distinctions for a reason - when they want to do something that (a) isn't provided in the support library and (b) isn't within the capability of the language, then its game over.

Regards, Tony

The proposal that we should act together to produce something that is possible is not at all of the form that we should strive together to try to produce something that is impossible.

I'll assume from your closing comment that you are unwilling to act in common cause with others on such a project, and that any further posts from you should be ignored as being irrelevant sneers?

I will consult and get back to you on that.

What you assume and what you choose to ignore is entirely your own business, Gary.

I wish you luck with your project.

Regards, Tony

...No comment.

Regards, Tony

I have consulted my acquaintance who uses C in both embedded and in PC applications, and who uses Visual Basic in PC applications and in Excel (for it was he who introduced me to Excel macros) and he suggested that I should ask you for examples of sophistication that you say are in the C language but that are not in Visual Basic, but without you resorting to unwise engineering wrinkles such as the conditional expression.

He says that Visual basic has Objects and that C does not, unless you take into account the little-known functions that can be provided as part of the definition of a struct.

Apparently, a C programmer relies on a large number of standard libraries, "stuff it can *call*" in fact!, especially the printf function which even has its own language interpreter built-in to deal with format strings.

It seems that one of the biggest sources of injecting viruses into PCs these days comes from the fact that Windows is written in C and that advantage can be taken by virus writers of array overflows on the stack, something that is not at all possible in Visual Basic that has array bounds checking built-in. So much for the superior sophistication of C!

Let us not take this too far, for it is drifting from model engineering, and I doubt my capability to win an argument against a software professional.

Functions as part of a structure definition, tell me more. I've not run across them in 18 years of C programming, but pointers to functions as part of a structure that I know about and have used before.

While true and the stack isn't the only place it can occur, that is something you have to be aware of when using the C language and it's simple to do. I've been programming in C for 18 years and do bounds checking but I've known many that can't be bothered and it does cause problems from time to time that could have been simply avoided.

Gary -

Thats probably the smartest thing you have said on the subject so far.

Regards, Tony

Sorry, but I'm not competent to answer that. Perhaps you in your turn have a more experienced guru to turn to?

Lets look at this logically. For anything to work to correct any errors it needs feedback in real time, actually it needs feedback in yestertime because if it detects a wander it'd too late.

Forget the computer operated plane scenario, they couldn't give a rats arse if it wandered off by 2" as long as it is still aimed in the general direction.

We OTOH need that last move , before it registered the error, to be correct., not going to happen.

So even if we can correct this we are looking at a set of glass scales at probably =A3600. we then need to read this information, digest it, run the algorithm, and send the new code to Mach or whatever other controller software you are running, then via the cheap unipolar driver to an ex printer stepper connected to the end of your hight tensile licorice router.

Please correct me if I have read this incorrectly.

John S.

I was hoping you might ask your acquaintance as you brought it up and he mentioned the capability. I don't personally know anyone I could ask but a quick google says you can't do it in C but can in C++. You can have pointers to functions in a C structure as I was aware of.

AIUI, what the OP meant (or what I am reading into his proposal) is that with a record of the known problems on any table, that we should pre-correct for those known errors in our calculation of the tool path. So we'd be talking about open-loop and not closed-loop control

I'm way out of my depth on this one and I'm not sure I'd understand what my guru is on about even if he did explain it to me. Is there a C based usenet newsgroup where you could ask this question and then report back?

OK, now understood but still at a loss to wonder why when it's easier and better to design and build the damn thing right in the first place.

John S.

Probably but I don't think it's important enough for me to do as I was happy with the result of google searching for "c structure function" and others had already asked the question and gotten the answer I mentioned above. Your guru doesn't need to explain it to you, all he would have to do is provide you with a C code snippet that shows a function in a structure that can be compiled with a C, rather than C++, compiler and you can post it in a reply.

One interesting possibility opened up by software is to use unusual engineering solutions that involve complex maths.

If you were operating a 3-axis machine by hand, I think your brain would explode if the controls were anything other than X-Y-Z.

But the hexapod platform has some massive merits, since positioning errors (and slop) aren't cumulative, in the way that they are if you place an X platform on a Y platform on a Z platform.

However, I defy any human to successfully operate a hexapod without using fly-by-wire.

At a simpler level, computer software can achieve linear motion from a non-linear hardware.

Consider a simple hinged gizmo (just a V). If one wanted to open it linearly, one would need a "quadrant leadscrew", so that turning the control screw was linear w.r.t. the angle of opening.

But with calibrated software one could have a simpler, and possibly cheaper, and more robust, leadscrew straight across the end of the V.

By removing the requirment for linearity FROM THE ENGINEERING, we open up the scope for different ENGINEERING solutions to a problem.

BugBear

'Yawn' --

Chris Edwards (in deepest Dorset) "There *must* be an easier way!"

e:

ay!" =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0

Sorry are we keeping you awake ?

John S.