Chuckranoplan 0003B and this Monaco thing

I’m going to Monaco.

Yes, that Monaco.

forever.

Actually, for EVER. See what I did there? The story of this one is that a few months ago, the MIT Scooter Party (all… three? of us) wrote a technical paper on how amazingly badass our collective scooterness is, and submitted it to the Electric Vehicles and Renewable Energies conference that is held in Monaco every two years. By some seemingly stochastic alignment of the universe, we were admitted to the conference.

So now we’re bringing the party to Europe. I swear, I’m going to run that F1 track-equivalent at least once on RazEr rEVolution. This trip would make RazEr my most well-traveled vehicle, since it also went to Singapore. As a microscooter, I guess it has an affinity for microstates.

I wonder if I can sell a few to Sealand.

Anyways, that’s tomorrow through Sunday. For now, Chuckranoplan!

Here’s MaB executing the best one-wall print I’ve seen it do yet. It’s printing the front end of 0003B as detailed last time. The walls are 0.5-0.6mm thick, and the internal spine is 1mm thick to allow for two passes. I was surprised at how well the Dual Integrated Bus Motor Mounts came out here.

Next I dropped the two middle segments on. I placed these two parts next to eachother such that their bottoms (keels?) were almost touching. That “encouraged” Skeinforge to make the layer changes and jumps at that point, and I must say it worked very well.

After all four segments were printed, I Dynamically Averaged (read: belt-sanded) smooth the interfaces and put them together with a CA glue initial bond, then Goop seal over that. The weight of this assembly is about 1.5 ounces.

A look down the tunnel of the hull before I closed it off. Having the ribs there prevented this piece from distorting and buckling all over the place quite well.

I split the tailplane into 3 parts and arranged them with the trailing edges close together. This view also shows the extra material inside to prevent warping.

The next effort was to print off the new wing design. This, unfortunately, turned out to be quite an exercise in futility for reasons which will be detailed. I’m not sure if it was the ambient temperature, the weather that day, or if I was sitting too close to it, but the prints failed repeatedly after two or three inches. The plastic would buckle, and generally with very little warning just completely delaminate with a very loud crack. It’s just a consequence of thermal cycling for a part this large.

Heated cabinet… heated cabinet… heated cabinet. Need to get on that.

Oh, ignore that McDonalds box. That’s a very warm spot, okay?! Once I have said heated cabinet, it’ll get even worse.

What happens when you try to print skyscrapers on a machine designed to print flats.

I have several ideas I want to try regarding how to prevent the severe thermal warping effects, including splitting the wing print in half laterially (so there’s a front and back half). I already tried splitting it longitudinally (to left and right halves), and it did work, but I also discovered…

z-axis drift

…that for some reason, the Z axis motor is not locked in one position during a layer. I’m not sure when this changed, or if it was always this way, but my Z-axis is now so incredibly smooth that it wants to fall back down the leadscrew.

The problem is that my layers are so fine (0.25mm) that even a sixteenth turn of vibration-induced sliding causes the smearing of an entire layer. I’d notice horizontal stripes forming on parts which were very large in cross section (noticeable on the tailplane prints). The machine loses enough layers such that the final part may be more than 1/4″ shorter than normal.

At first, I thought it was due to excessive friction on the Z axis causing the steps to fail. However, after lubing it up and noticing the problem getting worse, I concluded it had to be the opposite problem. So now I’m trying various things to increase the static friction on the leadscrew. The best solution would really be to make sure the Z motor is held with current during a layer.

The most severe vibrations happen on 45 degree passes when both axes are running at roughly 3/4 speed, so I may try positioning the wings horizontally or vertically after splitting them in order to minimize time spent moving both axes near the machine’s resonance peak.

How the hell did I manage to design a machine to so perfectly resonate at the exact speed I’m going to run it at?

 

Chuckranoplan 0003B: What’s probably going to take up the entire rest of spring break…

My initial goals for Spring Break:

  • Get the melontanktroller designed for LBS
  • Finish some summer project proposals
  • Finish an experiment and associated paper
  • Finish a paper for another class
  • Prepare for EVER 2011 (more on that later)
  • Whatever else minor project maintenance needs to happen.

What has actually happened:

Ah, productivity.

Anyways, with the relative success of 0003, I became more or less entranced over designing the next iteration. It was going to look much the same, but feature the internal printing trickery I explored for 0003, so I’m going to not designate it 0004 for now. It also doesn’t help that I bought yet another book on these things.  Maybe by the end of break I’ll actually know how they work so I can find employment building them after completely destroying this semester grade-wise!

The goal for 0003B is to keep the same overall layout as 0003, but make it powered. To that end, I’ve redesigned the nose and body to hold the two 30mm ducted fan units from 0002 and provide real electronics bays.

The nose is no longer a fully hollow shell, but now features a network of internal webbing that I guess is kind of like bulkheads and stringers. The Dual Integrated Bus Motor Mounts replace the dumb carbon fiber rod and hot glue mounts of 0002. The weight is still minimal, however. In ABS plastic, this part should weigh half an ounce.

After a few more hours of not paying attention to classwork…

I’ve added more internal spars to the wing shell, mostly to discourage the buckling and warpage seen in 0003’s wings. Note also the “electronics bucket” where I normally put a bubble canopy model. I’ll probably load this up with batteries and then cover the top with a strip of duct tape. Headless but flying Chuckranoplan is better than visually appealing but dysfunctional.

In addition, there’s one more design experiment being applied to 0003B, and that’s the attachment of the tail rods. In previous iterations, I designed the rods to be inserted into printed holes in the body. However, I’ve found that MaB really can’t build a perfect hole at all, and especially not at such a steep angle from the horizontal (printing the holes with the fuselage vertical means 60+ degree overhangs, which without support material, is very difficult). To fix this, I’ve located the rods just outside the body, sitting in angled and rounded channels. Now, the channels route as part of the outer perimeter, which means it ought to be much cleaner.

The same operation was applied to the tailplane. The center part, formerly with four through-holes, now has four edge slots. The idea this time is that I can actually mount the center piece first and check the angle before closing the rods off with the end pieces. So I don’t end up with another drag chute tail.

Also note the reduced amount of span members in the wings. I decided five was excessive and added weight which I needed elsewhere.

You would not believe how many tries it took to get this picture, since the simulator in ReplicatorG runs at 0.8 Mach. There exist Linux hacker ways of slowing it down, but I’m not in the mood to recompile a kernel, so I just kept recapturing the screen hoping to get a complete profile. And I did, finally. The above is a shot from a test route of the nose portion, showing the outer perimeter (just past one of the fan mounts), the internal cavity, and two underside reinforcement members being routed all as one single-wall profile. Ideally, if MaB just does this kind of thing for an hour, I won’t end up with gaps or thin spots.

Stay tuned…