so just from a design aspect heat cartridge close to the tip is advantageous
Yes, the closer the source of heat and the measurement of temperature is to the tip, the better the iron will be able to maintain temperature.
The higher the power, the faster the iron will be to respond, and the greater the energy you'll be able to transfer to the joint once the heat required gets anywhere near the amount of heat stored in the tip itself.
or ability to hold heat like ceramic or something that retains heat.
the greater the heat capacity of the tip, the longer it will take to heat up. Conversely, it will also make the tip slower to cool down when under "load"
Light weight I am assuming 50 grams?
that's pretty light. Check out the TS100. It isn't perfect, but it's pretty good.
balance is also a questionable item where do you want it balanced? in the dead centre? where you hold it? or somewhere else?
balance and comfort are more of a "feel" think once the soldering iron gets light enough that you're not expending effort moving it around.
Comfort is something that I could easily make as there is a possibility for something similar to a rubber grip
lastly the cable that doesn't get in the way might be hard for my special design unless I use something like a hook of to the side that keeps that chord up high.
Keeping the handle cool and having a handle that fits well in your hand are probably the most important. It's also important that there is no danger of your hand slipping down the shaft onto the hot bits.
the design I am going with is semi new currently I am looking at 8-10 chords coming out from the pen tip but heat shrink will bind them together. don't foresee it being thicker than mains chord but will assess it when I get the base unit sorted.
I hope the chords are pleasant to the ear. :-D
