Underactuated Rotor for Simple Micro Air Vehicles

I don't think the force on the rotor would change direction fast enough to cause a vibration. It would be more like a constant push relative to the intended tilt, or a slowly spiraling wobble.

I'm not a mechanical engineer, though.

Wrong, wrong and wrong. I'll start with the last "wrong" first. The third wrong (for your statement which only includes two issues) is for the typical, and ill thought process of technology. That it won't change, and it won't get better. It will, and it's doing so by leaps and bounds. 3d printers are quite literally coming out with new processes and equipment every single day. There have been a number of announcements in just the last few months that make it appear that even using metals for at home printing at an affordable rate may be possible in the next five years. There is such a fast rate of change and innovation, it's a bit silly to think that your comments on bad quality and materials won't change within the next year (if those comments were correct, they're not.)

As to materials, literally, every month, there are new materials coming out. At this point, I can use my desktop reprap to print ceramics, PET, Nylon, ABS (to just name a few), and all sorts of hybrids/specific compounds of these plastics designed for 3d printing. Nylon, PET, ABS are good enough for probably ~90% (very rough guess, sorry) of most of the plastic products in your home, it's probably good enough for most of the products I (and many others want to make).

As to precision, that's also quite wrong. The printers are quite precise. They're not as precise as the $75,000 CNC Mill that will get me .001" accuracy, but the truth is that most people don't even need .01" accuracy. And my printer cost me $500, quite a large cost premium there in terms of accuracy (ignoring the importance of cutting metal at this time).

As to doing CNC at home. Even a quite crappy homemade CNC mill, built on a real "mill"(something like a g0704) (not the laughable (to me) desktop mills that have come out recently, which are glorified dremels using similar methods of driving the axis' as a 3d printer, which you can cut aluminum at atrociously slow rates) is going to cost you at least $3000 (machine tools are expensive, not just because of the actual mill, but all the tool holders, bits, cutters, precision vises, calipers, etc. etc. that you also need to make it useful). So yes, a CNC mill is great for alot of things, but that homemade CNC mill isn't really going to hold .001 accuracy either, unless you spend a lot of time working on it and you really know what you're doing.

I'm not going to continue on with this argument, but it seems like your view of 3d printers and CNC milling is quite naive.

My $1500 home CNC will give .001" of an inch of accuracy. You'd be amazed how much errors in the .01s of inches stack up into unusable parts (try doing inlays with wood).

You are quite right that the cost of operation is quite a bit higher though. Bits, collets, spindles, etc really add up. Even with wood, all the tooling is made of solid carbide.

subtractive machining has its benefits though. While printing can make some unattainable shapes, subtractive machining gives a nicer variety of materials, and can be faster.

as to the more mature technology now, CNC definitely has 3D printing beaten, at both scale and precision. Hopefully soon, we'll be able to 3D print carbon fiber parts and then we'll have a real 3d printing boom.

Well, parts made in a powder bed printer don't typically have nearly as much grain, if any. I'm a big fan of that style printer in the future, so one solution to the problem is to use those instead.

For typical FDM/FFM printers like the hobby ones you see everywhere, there are chemicals that can be used to smooth the print out.

I use my parts for robot prototypes where the function of the part is more important than cosmetics, so I don't worry about the grain. If I want a nice part though, I can use very fine layers.

I should note, I have seen that site before. Looking at your comparison pictures, I have a couple of thoughts:

1) I am very aware that machining and casting makes higher quality parts. My point is that for all mechanisms there comes a point where the quality is "good enough".

2) The printed gears you linked to have abysmal quality. My 3 year old printer has made vastly superior parts. See this thingiverse part, with many high quality print examples from home printers: http://www.thingiverse.com/make:17409

I also used to be of the opinion that CNC machining was so superior as to render 3D printing useless. I looked at those stringy prints and said it would never be useful. But then, I slogged for years making CNC machined parts (see some examples of my parts here: http://www.tlalexander.com/files/portfolio.pdf ) and eventually decided to buy a 3D printer. I make more stuff now than I ever did when I had daily access to a CNC.

But as far as quality - notice how that stringy gearbox you linked to still seems to work? Sure, one is more photogenic, but the goal of a gearbox is to transmit power not win a beauty contents. Meanwhile I have been using a printed gear on my 3D printer's extrusion system for over 2 years with no sign of failure. The application is low speed but medium torque, and I see no wear or signs of weakening. The printed gear satisfied the requirements of the mechanism.

When I think of 3D printing, it reminds me of manufacturing in the 1940's. Parts were clunkier then, like the seat hinge on an old Volkswagen Beetle. But clunky works - often better. Newer techniques might make smaller hinges, but the one from the old beetle still works well. Sometimes higher quality isn't necessary to make something. A designer may choose to make something clunkier so that it can be made at home on a basic printer.

Another example- I use this coat rack and lamp mount every day: http://www.thingiverse.com/thing:16485