i found this interview buy guy about coils and rotaries,i found interesting
"TMN: Do you have any experience with pneumatic,rotary or half coil tattoo machines?
G: Several of my machines are half coil tattoo machines, and I like them for the weight difference... as I said earlier in the question about coil wraps, I have found that the amount of copper in the coils is a small factor compared to the rest of the machine's setup. If a machine is put together well it will run with more than adequate power even with half coils. The Fallen King irons I'm using have one full coil and one half coil each- interesting setup, a strange conclusion for a machine builder to come to... but they work great.
Pneumatic and electric rotary machines are another animal entirely. What I'm focused on here is what I refer to as a "stroke profile", where you imagine a graph of the actual motion of the needle as time passes. With a coil tattoo machine, you'll most likely find that the needle pauses for a period of time at the top of each stroke as electromagnetism builds, then when the magnetic power is adequate to overcome the spring tension, it suddenly pulls it down. As the armature bar approaches the coil, its distance decreases, hence greater magnetic pull as it moves downward... so in effect, the needle pauses at the top, accelerates toward the skin, then pulls out immediately without any kind of turnaround time. With any rotary tattoo machine, the opposite happens- the needle is always in motion in a smooth oscillating motion, meaning that the needle is actually slowing down as it approaches the skin... it slows down to a stop, then speeds up again gradually as it pulls out. In some ways, the needle strike of a rotary tattoo machine is the polar opposite of that of a coil tattoo machine. What this translates to is that with rotaries, the points spend more time in the skin, so the tattooist needs to adapt their hand motion to this or there is a continual sense of the needles snagging the skin. Many color realists have found that this modified hand motion lends itself to their working style perfectly, although I find that it cramps the style of my rapid hand movements, which I like to keep uninhibited.
Todd Myers from Morphix and I spent a day doing ink flow experiments with a variety of tube tip styles, including some prototypes. To be thorough, we tried these tests on a number of machines including a Neuma Hybrid. I found that the Hybrid scored up to 50% better on ink flow than the other machines. I suspect this has something to do with that slow oscillating motion- at the top end of the stroke it slows down, picks up pigment, then speeds up again as it heads back down, while a coil machine enters and exits the tube tip far more abruptly. My wife Michele is using the Hybrid and finds that she can hang the needles an extra millimeter or so out of the tube without them getting too dry. So each type of needle motion has its advantages and disadvantages.
It's worth mentioning here that the Hybrid has a cam system that I helped design and am listed on the patent as a co-inventor... it has a progressive cam geometry so that the needle spends 40% of its time in the lower half of the stroke and 60% in the upper half, more closely emulating the action of a coil machine. We're working of further ways to emulate a more idealized stroke profile. Until then I'm still using coil tattoo machines. I believe that the answer lies ultimately in a totally new kind of tattoo machine that combines the best features of both worlds"