Uploading custom firmware to the 1.4 ramps?

Hey guys!
Im building a 3D printer and Im going to use ramps 1.4. There is only one problem, how can I custom upload the firmware to the board?
By that I mean how can the firmware know the bed size and how can I tell the firmware about my step motors quality and my timing belt spacing?

There's nothing unique about what you are trying to do. Most reprappers out there tweak the firmware and upload it. Its just an arduino board so you can upload firmware many different ways. The easiest is probably the arduino IDE but there are alternatives.

Thank you for your answer, but what i dont understand is how can anyone make a 3d printer then?
let say Im designing a 3d printer and i want my timing pulley to be t2.5, 16 teeth, but at the same time someones else is using the same board on their 3d printer which got the timing pulley size of t5, 10 teeth. How can I tell the firmware about this sizes?
You also mentioned about how some reprappers tweak their firmware and upload it, where do they upload it, is it possible to send me the link?

Get the arduino IDE, and get a copy of the firmware of your choice. Marlin is good. Or sprinter. I hear good things about Repetier as well.

Open the firmware in the IDE, work through configuration.h to set it up for your printer, select 'arduino mega 2560' in the board option under the tools menu, and press the upload button.

The firmware doesn't need any of that kind of information.

[reprap.org] Is where you set up distances and other things to say how far things are. Its not as near as complicated as you are thinking with the belt teeth numbers and such.

Actually the firmware needs precisely that information.

You should probably read up on the arduino and what you can do with it. The ramps board is simply a shield that sits atop an arduino mega. The arduino is where you actually load the firmware. Download the firmware of your choice - marlin, sprinter, and repetier were mentioned - and load it into the arduino IDE. The firmware is simply c++ code. Make your configuration changes, and instruct the IDE to upload.

It may seem mysterious to you now, but once you do it a few times, it will seem straight forward.

Edited 1 time(s). Last edit at 10/06/2013 11:33PM by jbernardis.

Thank you for your answer @jbernardis!
I will see what happens

Ramps 1.4 is an Arduino shield... It is the interface board to connect stepper drivers and stuff to your Arduino. The Arduino is what gets the firmware from the Arduino IDE to run what is on the shield. Marlin is one of the popular firmware versions.