Archive for the 'Chibicopter' Category

 

The Post Where I Update Everything Ever, Part III: What’s Smaller Than Tinycopter?

Mar 14, 2012 in Chibicopter, Project Build Reports

Chibicopter!

The game is on. I’m out to build a quadrotor smaller than Tinycopterway smaller. This isn’t anything that new or groundbreaking – it’s been done before, and even smaller than my 2.5 or 2″ prop size, but this is my project, dammit! I have never thought of anything on the scale of where fractions of grams will matter, or where the control bandwidth is potentially far above the maximum refresh rate of R/C based controllers. Either way, this is going to be one hell of a challenge.

And furthermore, I’m doing it for the Design for DIY Manufacturing course (MAS.963) at the Media Lab. So, once again, a chance to pimp all of those rapid prototyping tools I have come to love so much. Now, there’s some issues with the whole “Charles builds something for class” thing which historically have caused problems, such as me focusing way too much on the build and not enough on the class, but I think it will work out in the end.

This project has actually been running for about a month now. I started in February by designing the airframe:

That cutout in the middle is an XBEE. That’s how small this thing is. The airframe is designed to be one piece SLS 3d printed in nylon – this is not a technology that is available here, so I have to farm it out. No matter – I can’t get the frame light enough while still adhering to the minimum feature size requirements of FDM printing. The frame weighs only 8 grams in this image, but later on I reduced some dimensions and wall thicknesses and got it down to 7.1. It’s still a bit “chunky” looking, and I’m sure with MOAR SCIENCE I can improve the rigidity of the arms even further and make them even narrower, but unlike some MechE designers who insist on characterizing and justifying every single aspect of the design by analysis and simulation (Deterministic Design™), never actually getting around to building the damn thing, I strongly favor just forging onwards with something that looks good and later on analyzing why it worked or didn’t work.

The underside is essentially all hollow – a single board will be mounted in the middle which will carry the XBee, an embedded ATmega328 microcontroller with required peripherals (since I can’t stuff any kind of Arduino module on this), and four 1S, 3A ESCs from Hobbyking which will be partially embedded on board by virtue of hanging off via headers. A Pololu miniIMU will also be mounted on the board. The all-up weight of this thing ought to be under 50 grams. The motors were selected to be 2 gram outrunners from Hobbyking, and I also bought a few 240mAh and 160mAh single Lipoly cells for the battery, which will probably just be parked on top of the Xbee.

Now, let’s fast forward 2 weeks after Shapeways finished producing the frame in their magic SLS printer (probably an EOS Formiga or similar). The airframe only cost $13 to print, by the way, because the material use is so little.

GUYS THIS IS THE CUTEST THING I HAVE EVER DESIGNED LOOK IT’S SO ADORABLE AND TINY AND SUPER KAWAII MOE MOE DESU AND STUFF

Wow, this is smaller than I imagined. Also, the frame really is kind of flexible – they weren’t kidding when they said white, strong, and flexible. Part of the flex comes from the completely open bottom and non-closed arms – I was originally intending to route wire inside the airfoil-like arms, but I really didn’t need to make them all the way open on the bottom. That was a slight design derp, but while the frame is bendy by hand, my hand also exerts far more force than it will ever see on its own.

It’s also fixable with a chunk of balsa wood and some super glue.

OH MY SWEET ROBOT JESUS IT’S EVEN CUTER WHEN IT’S NEXT TO TINYCOPTER I THINK I’M ACTUALLY GOING TO SQUEE OUT LOUD GUYS

Yeah. Also, in other news, Tinycopter still exists – it gave a full day of flying demos at the MIT Museum recently, which surprised me since 1. it worked the whole time and 2. I flew it the whole time, somehow.

I got the outrunners and other parts just the other day. This thing is just going to be a ball of cute. The outrunners are 8mm in diameter, and the stator is like, no more than 5. How the hell do you even put that together? The 2510 props just press right onto the 1mm shaft. No prop collets or savers or anything.

Here’s a 240mAh cell. I might downgrade to the 160 if weight presents a problem, but the 240 is nice because it fits within an XBee’s footprint. I’ll probably just end up patching a JST-ZH or similar miniature terminal onto the end of this thing.

The next step is to whip up the single board and have it fabbed ASAP – I’m running quickly into the “midterm” project demo due to everything else that’s going on.