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Underactuated Rotor for Simple Micro Air Vehicles

modlabupenn.org

81–84 of 84 posts

Re: Underactuated Rotor for Simple Micro Air Vehicles

#81
Reminds me of PWM [1] on old PC speakers. Many old computers (e.g. of the 286 era) had a speaker that was only able to generate square tones. By controlling the start and duration of the pulses, programmers could generate sounds that were a lot more rich than what you would expect from "plain" square waves [2].

In a way this is similar: they start with two actuators that seem very limited in what they can accomplish: you can only speed them up and down. By modulating the speed of both motors in sync, they are able to control that cheap rotor mechanism they came up with, achieving 6DoF [3]

1: http://en.wikipedia.org/wiki/Pulse-width_modulation

2: https://www.youtube.com/watch?v=FSe3ysBrXq4

3: http://en.wikipedia.org/wiki/Six_degrees_of_freedom

Re: Underactuated Rotor for Simple Micro Air Vehicles

#82
post #67
post #43

Earlier quoted context omitted.

i was about to propose some sort of annealing process like they do with metals, and it seems like someone has already beaten me to it: http://3dprint.com/3388/study-how-to-make-3d-prints-stronger... as a side note, this looks like kind of a cool way to smooth pla prints, for which up till now there wasn't really a great option.

that is a horrible article, considering the picture they are using is ripped off of a reprap blog on smoothing abs prints using acetone vapors. http://blog.reprap.org/2013/02/vapor-treating-abs-rp-parts.h... . (I'm actually a member of Fablocker, so I'd seen those squirrels before)

well shit. we tried putting some big pla prints in the oven last night and they definitely just started warping and caving.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#83
post #82
post #67

Earlier quoted context omitted.

that is a horrible article, considering the picture they are using is ripped off of a reprap blog on smoothing abs prints using acetone vapors. http://blog.reprap.org/2013/02/vapor-treating-abs-rp-parts.h... . (I'm actually a member of Fablocker, so I'd seen those squirrels before)

well shit. we tried putting some big pla prints in the oven last night and they definitely just started warping and caving.

on that note though, from my experiments, acetone vapor bath does seem to strengthen abs prints some, cause it melts the surface together. Not terribly big effect, but it actually helps a lot for low infill parts and stuff.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#84
post #75

Earlier quoted context omitted.

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 announcement…

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…

Don't get me wrong, I'm also a machinist, and I do use subtractive machining quite a bit. And I'm guessing your CNC machine is a router, not so much a mill (to make life easier, I'll classify a mill as having a much larger Z-axis movement, and built to deal with harder to machine materials (steel essentially.)) And in that case, it's much easier to get a router to hold smaller tolerances than something that's designed to handle steel. Now I could be totally wrong, and if so, props to you, you got a deal. But really, even the cheap chinese mills (again, talking about something like the Grizzly g0704, maybe the Sieg X2) I've seen that (sans CNC equipment) start at around $1000. And once you add on ball screws, servos, and all the control hardware, you're pushing $1500 easily. And like you said, then you have to actually buy the tools you need to use it.

But while prices on CNC mills are getting cheaper, I'd argue that they aren't declining in price the way that 3d printers are (my reprap cost me $400, my makerbot clone $550). A mini-mill still costs more than it did 10 years ago, with very little improvements to what it does (better motors, electronics, that's about it.)

But to put it simply, I agree with you. Subtractive machining has it's place for sure, but so does 3d printing. But to say that 3d printing sucks, period, is just silly and ignores all the benefits that 3d printing provides. I believe in using the right tool for the job. Sometimes that's old school machining, some times it's 3d printing.

I'll add two quick, somewhat off topic points. It's now (apparently at least, according to GE) easier for them to additive manufacture turbine blades made out of inconel than it is to subtractive manufacture them. I've never had to machine inconel, but from what I've heard, it's quite the difficult thing to do, and most places that machine it, try to cast the part as close to net as possible to make as little machining as possible to do so. But this is something that truly shows the advantages of 3d printing that (might) be better than the traditional way of machining.

The other anecdote is my own. The other day, I was making a part, and for shits and giggles, I took the blueprints, made the part in CAD, printed it out on my 3d printer, and just the act of holding it in my hand and looking at it really helped me think about how to go about machining it out of steel. Most people think "On, CNC is easy, you just throw the file on the machine and it makes the part." It's not that easy, and I was just doing this part on a manual machine. But having that part in my hand really helped me make better decisions on how to best machine the part itself. I thought that was a neat little aspect of 3d printing that I would have never even thought of using it for.

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