Size and self awarenes

Hey all!

I've been reading around here about sizes of the reprap. From wat I found the problem is that the plastic is cooling and shrinking if you have a to big object to print. Now, what I'm wondering is. If you don't look at the problems of the materials you are building with. Is it possible to scale the reprap design up to larger designs? Does the electronics and the software handle this automatic or is sizes hardware coded into this in some way? Will it figure out it's own size (XYZ) automatically or is this something that will need tweaking?

Im planing a pen drawing bot based on the reprap design. I'm looking for sizes like 3m x 2m sizes if possible.

Hi Martin,

... you have only to measure and scale the step-per-mm-ratio when you change the frame-size or gears.

The only problem with very large objects and high accuracy could be overrun of the coordinate-values when driving past the highest possible value - i didn't know, what type (long int, double or higher) is defined actually ...

Viktor

VDX Wrote:
-------------------------------------------------------
> The only problem with very large objects and high
> accuracy could be overrun of the coordinate-values
> when driving past the highest possible value - i
> didn't know, what type (long int, double or
> higher) is defined actually ...

Hi Viktor.

This sounds promising. But I don't really understand what you meen by this quoted part above. Can you explain it again?

--
Martin

The firmware of the driver circuit stores the position values in a variable,
to "remember" where the toolhead is at this very moment.
variables can be defined so that they hold different types of informations.
Some of which are smaller than others,
for example if it's defined to be a boolean it can only hold "0" or "1" not more, not even "2" (because that'd require a second bit, and it can only have one)
if it's declared to be a LONG it can hold 16bits afair not more.

So there is an upper limit for values that you can store for positioning;
If you go "longer" than that your bot will not work.
(not without new firm-, maybe even software)

'sid

Thank you, now I understand the problem.

I'm planing to use the g-code firmware for the arduino. I'll try to look at the code and see, but if anyone have an idea about how the variables in the firmware is, then please let me know.

--
Martin

Sid,
Long is a least 32 bits on any processor I have used.

I don't know what the latest frimware version uses but there have been issues with the z-axis being too big for 16 bits if you half step. Not sure if that is fixed in the latest version yet.

---

[www.hydraraptor.blogspot.com]

you're right 32..
8bit = 1 byte (8); 2byte = 1 word (16); 2word = 1 long (32 !)
2long = 1double (64) and so on ...

What about storing positions not steps... is that viable?
(steps is a 160times larger number)
probably not...

'sid

Edited 1 time(s). Last edit at 11/28/2008 09:28AM by sid.

... long should be enough - it's a count of 4294967296 steps or 4294,97 meters (or 4,3 kilometers) per axis-variable when measured with an accuracy of 1 micron!

Viktor

Edited 1 time(s). Last edit at 11/28/2008 10:06AM by Viktor.

>2long = 1double (64)
Not really, a double is a floating point number. 2float = 1double usually.

For a 64 bit integer it's long long.

---

[www.hydraraptor.blogspot.com]

float point yes.. but 64 bit for sure

'sid

hmm so I can conclude that it would work and the variable is not a problem?

Hi

I have run into a problem with Arduino and variable size as I am using micro stepping drives.

I understand the firmware at the moment uses Integers storage, and stores a 2
byte value. This yields a range of -32,768 to 32,767 (minimum value of
-2^15 and a maximum value of (2^15) - 1).

I understand there is a plan to increase the variable size in the future but that both the host and firmware will need changes.

---

Regards

Ian

... ooops - a variable-size with 16 bits means 6,55 meters with an accuracy of 0,1mm or 65,536 centimeters with 0,01mm accuracy - this could really be a problem ...

Viktor

How much accuracy is necessary?

I'm thinking that 0.1mm is quite enough, but I have no experience with this so I might be wrong. That is considering that the pen I will use for my drawing machine is probably around 2mm itself if not larger.

--
Martin

Hi Martin,

old plotters had normally a resolution of 0,025mm (1/40 mm) what was enough resolution for pen-drawing but not enough for laser-cutting.

My CNC-mill has an accuracy of 0,0125mm with halfstep or in single micron-range (or even sub-micron) when driving with microstepping (i have 1/8- and 1/256-microstepping-drivers).

So a conclusion:
- for a 'perfect' resolution where you didn't see any aliasing with reprapping 0,1mm are enough
- when plotting with the same system you should have 0,05 or better ...
- for milling or laser-cutting you should have 0,01mm or better ...

Viktor

Thanks, that was clarifying