Archive for the 'Fankart!' Category

 

Fankart!!! 3: Better than Fankart!!! 2

Jul 16, 2010 in Fankart!, Project Build Reports, Stuff

Fankart has turned out to be a concentrated form of the kind of projects projects I’m used to building. It was originally built as an engineering joke, it’s only been existence for a week, it’s utterly useless, and it’s already more internet-famous than it deserves. I mean, even LOLrioKart took a full year before people finally noticed how utterly useless it was. Then the Internet fame is at least somewhat warranted.

And RazEr has never been Internet-famous because it’s actually somewhat useful..

I don’t know what I keep working Fankart. Probably because the time delays between when I ordered parts and upgrades to when they actually arrived have all expired within the past week, so I had an essentially continuous stream of resources to keep working on the HFFan. In my opinion, the HFFan in its latest iteration (to be detailed, of course) has almost reached the limit of what I feel like building without actually engineering something. The whole point of the HFFan, originally, was to see what I could pitch together given only McMaster, Hobbyking, and laziness. To that end, it has accomplished more than I had planned.

I got a set of 16×10 propellers from Hobbyking along with my latest impulse purchase. The accidental perspective makes it harder to discern that they’re larger than the 13×8 props in the foreground – but rest assured, they’re bigger.

The idea is to cut these back down to ~13 inches in diameter such that the portion left retains most of the original’s steep pitch.

Oh, about that impulse buy… Remember when I was talking about the Hobbyking 80/100 “HKrunner” before? They are so rarely ever in stock that to actually see a positive number on their stock count is like sighting a carbide-tipped parabolic flute unicorn. But last week, it finally happened – by the time I saw it, there were six left.

Along with motors #3 and 4 for the HFFans, I snagged two HKrunners. The shipment at this point was probably a few kilos short of when it had to go ocean mail, and shipping fees came out to $100 alone.

My bank probably just shit itself and wiped using my checking account. But, now I have two HKrunners.

What ever will I do with them?

HKRunners aside, I began on boring out and trimming the propellers.

Problem: Even the largest lathe I had access to at the time couldn’t…er… swing the props, since they were too large in diameter. And so, I had to cut the tips off using a bandsaw first. The line indicates roughly where “13 inch diameter” is.

Then came the drill-to-12mm process on the heavy \m/etal machine.

The fine trimming process was the same, except this time I used a straight-fluted cutter on the highest speed to avoid the up-and-down flapping of the prop blades that had occurred last time.

The straight-fluted cutter in question was actually a reamer.

… and the new props drop right into place!

The tips were trimmed to less than .02″ clearance this time. Legitimately, I mean – last time, I forgot that endmills have diameters, and came up 0.050″ too short!

Here is the HFFan with the new propeller setup and a new lower mounting position! It turns out that the whole thing fits snugly between the uprights on the cart frame, blocked from forward movement by one of the basket spars.

The same fiber tape I had used to retain the duct in arrangements past sees a return here, pulled as tightly as possible. The whole setup is reasonably stiff, despite not looking like it should be.

Hey, at least now the basket is empty and ready to accept groceries!

The rear view.

Note the scrape marks in the duct – it turns out that even though trimming the props to sub-millimeter clearances was done with the best of intentions, the high-tension tape mounting still causes the thin PVC to deform some.

I decided to not play the tension adjustment game and just let the prop break in its own duct by running it at full bore until the skull-grinding noises stopped. Now that‘s engineering.

The heavier pitch, longer chord, and tighter duct are all reflected in the increased power draw. Clearly, the 18 gauge battery leads are the bottleneck in this system – the voltage drooped to 31 volts under the highest load. Should it have held relatively steady, I would probably have seen the 3 kilowatt mark.

steering the fankart

This is failrudder.

After I got sick of retying the front wheel knots (or having them retied), I started throwing together other possible solutions for steering. One of them was this dead-fish-esque rudder, made by zip tying a cut piece of copper-coad fiberglass board to a servo zip tied to the frame.

No, it did not work. At all.

Next, here is differential failbrake. Real airplanes generally use differential braking force to turn using their propellers or jet engines (for single engined planes), so I figured why not try it on fankart?

Well, it would have  probably worked if the brakes weren’t raw servo horns, the servos weren’t mounted with zip ties and tape, and the wheels didn’t have so much slop they could tilt 10 degrees off axis and still rotate. Those are some seriously worn-ass wheel bores.

All things considered, I just decided to retie the damned servo knot to test Fankart 3.

So here it is – the collection of test video from the past two days or so!

Yeah, that didn’t end well. Something about “night time and shadows obscuring the unforgiving curbside of life”.

There was no major (or expensive) damage to anything. The HFFan just flew off, and surprisingly, all the electronics stayed in the basket.  Maybe I’ll throw it back together and actually try testing during the day some time… New concept, I know.

What’s next for Fankart?  I’m not really sure, but one of things I still want to do is get an actual thrust number on the HFFan. If it’s two digits, I’ll consider making more. If not, it’ll become the next high-five machine. I’m pretty stoked by the fact that the latest HFFan could accelerate the whole thing up a roughly 6 or 7 degree ramp faster than the previous could accelerate on flat ground.

FANKART!!! 3

Jul 14, 2010 in Fankart!, Project Build Reports, Stuff

Hello Internets. I don’t know why you’re so fascinated with random things I throw in shopping carts (probably because of LOLrioKart), but I think you should check out my projects which have marginally more value to society (debatable, of course), such as RazEr or its ‘blades derivative. Or the battlebots. Or hell, even my dumb glowing safety goggles.

But anyway, here’s Fankart in its latest mid-engine flying configuration.

After the epoxy joint failed, I busted out my all-time favorite adhesive – Automotive Goop – and rebonded the motor mount to the duct. The new joints are substantially stronger and have the benefit of being mildly flexible, such that squeezing the duct no longer caused brittle failures. The battery was moved underneath out of packaging issues, and the fan now sits in the basket, retained by the pressure of being shoved between the wire basket frame, and by a (difficult to see) fiber tape strap that goes underneath the structure. And by virtue of its own thrust.

No videos of this version yet, nor any thrust numbers from the fan itself. I’m going to build a thrust-measuring rig (scientific rigor to be determined) to see what the specs on it are. Two 16×10 props are also on the way, so expect more  ファンカート!!! action later.

More about Fankart and the HOLY FUCK!ted Fan

Jul 10, 2010 in Fankart!, Project Build Reports, Stuff

So this is where I expound on the gory details of why there is now a propeller-driven miniature shopping cart buzzing around campus.

The reason: Well, there is no good reason. Is there ever a good reason for anything I do?

Fankart actually has a bit of history behind it. At least, the fan part does. A few months ago when the semester was winding down, I made a post about the proposed ground effect vehicle Chuckranoplan. With me having no aero/astro design skills to speak of, nor meaningful experience operating either airplanes or boats, it was an idea that was bound to end in significant accidental property damage and probably some personal injury too. But the dream lives on.

Researching the vehicles, though, got me interested in aircraft and marine propulsion. For instance, I now have an itching desire to build a Voith-Schneider cycloidal thruster, which is something slower and more Meche-intensive. The other end of the curiosity thread was ducted fan propulsion. Electric ducted fans have been in use for many years on model aircraft, but only recently have they started getting huge because of the power levels the hobby has risen to.

Huge and Electric are two words that appeal to me greatly. Couple that with my history in combat robots which has caused me to lose all sense of self-preservation around high-speed spinning objects, and it meant that I was going to build a vehicle with EDF thrusters sooner or later. Plus, since Chuckranoplan was destined to be electric, it was good practice.

Then came word of MIT Talaris.

In short: Electric ducted fan supported platform reduces the apparent weight of the experimental lander vehicle by 5/6ths in order to test operation in the Moon’s gravity… without actually, you know, going to the Moon. After being shown their test videos, I decided to build myself a ducted fan thruster that was bigger than theirs.

That’s it. That’s the entire reason I’m doing this – so I can have the biggest EDF array on campus. After all, I can’t work without a false sense of competition and engineering machismo.

caution: no aero-astro majors were harmed in the construction of this travesty of engineering. course 16 discretion is advised.

The HOLY FUCK!ted Fan, as it became known as, has been in the works for about a month. By “in the works” I don’t mean real engineering such as fluid dynamics simulations, airfoil selection, motor analysis, manufacturing studies, or any of that. I meant sitting on HobbyKing and window shopping for a few nights.

The overarching goal was getting the most static thrust for the least effort and money. One ducted fan unit (without the motor, even) on Talaris runs a cool 500 dollars. Thrust, as I understood it from Wikipedia and hopefully accurate information from random friends, tends to increase more quickly with diameter than speed. So at the outset, I steered away from having actual ducted fan blades towards what would be better described as a shrouded propeller; that is, using a stock or slightly modified propeller in a tight-fitting circular duct.

The duct would be Schedule 5 or 10 PVC pipe – otherwise known as PVC ducting, used generally in laboratory settings for corrosion resistance where your vapors would eat fucking metal. The wall thickness on duct of this size is 3/16″, which was significantly better than the 7/16″ seen on common Schedule 40 for the size ranges I was considering. The duct alone would weigh more than the Sun.

I decided to begin small – and by small I mean 12 inches across with a power level in the 2 to 3 kilowatt range. After all, if I build it too small, it would overlap with real ducted fans. I decided to try stacking two three-blade propellers to get what amounts to a 6 blade propeller, with caveats such as “it wouldn’t actually be as good as a three bladed propeller of marginally larger size” and “the rear prop would just catch all the turbulence coming off the first”. It just had to look mean. Be glad I didn’t go with THREE stacked props.

What you get: shiny thing, shiny thing, shiny thing, shiny thing, and a tacky sticker sheet

The motor choice was pretty simple. I’ve actually been meaning to write up a post about the newest line of Hobbyking mutant outrunners, because they are actually legit hardware. These motors feature a full “distributed LRK” (i.e. 12 slots, 14 magnet poles) winding with almost outrageous slot-filling percentage, achieved by paralleling many fine strands of magnet wire in a quasi-Litz fashion. The massive external rotor is double-supported, on one end by a conventional shaft bearing and on the other by a ring bearing. This means that they no longer have magnet-ditching issues, which was a sour point with the previous generation of ICBMs (Inexpensive Chinese Brushless Motors)

In other words, it’s like Deathrunner but cheaper, better, and mass-produced – HKrunners. I’m pretty much going to use them on everything now.

The baddest of the bad is the 80/100 size, which (besides actually having a 68mm x 54mm stator) weighs 4 pounds and can briefly suck down half a dozen kilowatts. While I already had access to a few of these in the Media Lab because we are converting them into drive motors for the world’s most awesome Powerwheels car EVER, I decided that using a mere 13″ prop on something this huge is just a waste of the motor. Those motors swing 2 foot propellers on model planes 8 feet across in wingspan. When you build a model plane that big, can’t you just get in and fly it yourself?

I settled on the polyp stage of the 80/100 motor, the 63/64. They’re a miniaturized copy of the big motor, and use the same stator size that I used in the skatemotors. In fact, I briefly considered just hacking up a few of them for use in RazErblades, but decided to press forward with the custom motors anyway.

The 280 RPM/V rating ought to net me a bit over 10,000 RPMs at 10S lithium batteries.

I got a pile of Master Airscrew 13 x 8, three-bladed props to start with. When I received the shipment, it was just too tempting to resist pitching a prop on the motor and spinning it up. You can’t grab onto an outrunner when it’s spinning, since the case moves. So I used the included face mounting flange and… well, bolted it to a table.

And stood behind a 1/4″ polycarbonate blast shield.

Watching a spinning propeller isn’t really funny or insightful, so I’ll spare the test video.

Here’s the 12 inch PVC duct from McMaster-Carr. For reference, it’s part number 2051K75, which actually seems to be not a duct in its own right, but a connector for two ducts.

The ID was larger than I anticipated – meaning that it was not a 12 inch pipe, but to go around a 12 inch pipe. The props still need trimming to fit inside, which meant it wasn’t a total loss.

Now I needed to make a custom prop adapter that could hold two stacked propellers. The stock prop mount that comes with the motor suffers from a few issues, such as

  • being made totally of aluminum. Soft aluminum.
  • bolting to the face of the motor without an aligning boss… well, there was one, but it was rather ill-fitting
  • not being long enough to fit two propellors.

All the reason to make one, of course. Pictured above is a bag of M12 bolts, 12mm shaft collars, and some conical washers. I’m going to revert again to the tactic of the split-tube-collar shaft adapter, as seen now on my Die Holder of Convenience and Überclocker 1′s arm drive.

The concept is simple: drill a hole in a larger shaft that is the diameter of the smaller shaft. Slit the larger shaft, then drop a collar over the slit and crank it down. Simple, adjustable, full-contact, and compact.

I decided to splurge and buy some special tools just for this purpose. Along with the McMaster order came a 12mm drill bit for boring out the props to fit the bolt, a 10mm drill bit to hollow out the bolt, and a 0.040″ thick slitting saw. I had to fight my sense of never-buy-specialized-tools-you’ll-only-use-like-once because there was really no other way I could realistically put a 10mm and 12mm hole in something as quickly as with bits that were already that size.

I mean, I couldn’t even waterjet this, and doing it the professional way without a dedicated bit, such as with a generic boring tool, would take longer than 1.2 seconds.

Here’s the first double prop adapter undergoing the slitting operation after being drilled. I got to break out my haute usinage indexer, mostly as a horizontal protruding mount for the bolt.

A completed prop-bolt…

… slipped over the motor shaft and clamped solidly. Gee, this is so convenient I might start doing it for everything that might need attaching to a motor.

The flower of death blooms.

Or something like that. The two props slip on the 12mm bolt and are retained by the stock aluminum prop washer, one spring washer for preload, and the stock M12 nut.

I ordered enough materials to make two propeller assemblies (but not two ducts!). For the next motor, I decided to try rearranging it inface mount mode. Motors like this can be mounted inside the plane (“firewall mount”) or outside (“face mount”). In the former mode, the propeller is on the opposite of the mounting surface as the motor, and in the latter, the motor and prop all hang off the mounting flange.

Straight-up mechanics would dictate that the latter mode is almost always less stiff, but it was worth a shot. To move the shaft on the motor involved undoing the shaft set screws, removing the small retaining ring on the underside of the stationary base , then using a 2 ton arbor press to barely move the shaft through an inch to the other retaining ring groove. That center shaft is well installed.

The “face mount” mode complete. While the machines were warm and set up, I just went ahead and blitzed both prop adapters.

this is where it all went terribly wrong

“I need something to mount this to so I can spin it up.” -me

“Why don’t you just use the little cart or something?” -MITERer

I mounted the motor to the minikart by sandwiching the wire frame using the other motor’s removable flange. Four 10-32 bolts held everything in place. I wasn’t worried about the motor flying off, just… oh god, everything else. Into the basket went a 100A Turnigy HV controller (my favorite, and RazEr’s heart), my spare BR6000 receiver from Cold Arbor, and either a 7S A123 pack (also from Arbor) or a massive 10S, 10AH lithium ion battery pack.

Yesterday’s post contains that test video. It was funnier than it should have been.

After I finally came to terms with the spinning propeller, I was more comfortable gunning it to full throttle. Funny thing – I have no problem operating and standing around machinery that spins solid hardened steel blades at several thousand RPMs, but am chickenshit over a piece of plastic or wood. All things considered, I think a plastic fragmentation grenade is less painful than a hardened tool steel one.

The best run of the night!

The 10AH lithium pack was big in capacity and all, but it had 18 gauge wire leads. That means it couldn’t flow nearly as many amps as the batteries are capable of. The numbers could be higher, but 2kW is getting close to the “maximum recommended” limit for the mini HKrunner.

(more…)

Fankart!

Jul 09, 2010 in Fankart!, Project Build Reports, Stuff

…because FANKART!