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

Friday, July 16th, 2010 @ 4:31 | 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.

 

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    11 Responses to “Fankart!!! 3: Better than Fankart!!! 2”

    1. Mike L Says:

      btw, what website do u order industrial parts from, u know, put in manufacturer and part # and it gives you a quote, im looking to buy some a123 m1 cells. thats awesome, you cold probably measure thrust by standing on a scale with it, then again with it on and find the difference.

    2. the chuxxor Says:

      McMaster-Carr is the closest to what you describe, but they don’t carry A123 cells.

    3. Joshua Cole Says:

      I figured you might appreciate this:

      http://www.youtube.com/watch?v=Jb8T-TqvNVE&feature=player_embedded

      That looks like a challenge to me!

      (82KOhms) =]

    4. Mike L Says:

      i was wondering a bout something, you see, ihave an i-zip 130 scooter and the prob is the motor is too weak for my weight, im thinking about buyin the turnigy 50-55A 400kv bdc motor and a controller since this motor is the same voltage and is even smaller in dementions than the previous one and has the same shaft size. i was wondering though how i should mount a D shaft pulley on a circular shaft or if i should just get a motor with a smaller shaft and make an adaptor from a piece of metal, i dont know how i would though since i have no access to a lathe or any other machine other than basic tools. i also though that i could drill out the D shaft pulley into a circular one andpress fit it, but i am worried that the shady chinese pulley would slip under the amount of power its under(3 times the speed and 3 times the torque), so if you could give me your advice it woud feel great, dont feel obliged like you have to respond, il probably figure it out somehow.

    5. Mike L Says:

      sorry, i meant “be great”, not “feel great”, that would be wierd.

    6. the chuxxor Says:

      D-bores are notoriously difficult to make circular without a machine tool or fixture because they will cause almost all tools to wander, due to their asymmetry.

      I wouldn’t press fit a motor of that power level. They do sell pulleys with metric bores and set screws built into the hub, by the way. Check sdp-si.com and their online store. That’s what I’d do if I had no tools and a bit of cash lying around. The Currie izip most likely uses a common “5mm HTD” timing belt, so you’d be seeking a 5mm HTD pulley of your desired size and bore characteristics.

      If you do end up using a stock pulley with set screw, grind or file a flat area or two onto the motor shaft. Otherwise, your set screw will be pretty weak.

    7. Mike Says:

      thanks, i know from the motor specs that its a 3 mm pitch cogbelt on a 15 or 16 tooth pulley, im also lookin at some 3 cell zippy lipos to boost capacity from 24 v 5 ah with stock SLA batteries to 24 v 20 ah

    8. Mike L Says:

      sorry posted twice, my browsers didnt update first time

    9. Martin Diehl Says:

      Hi! I think to fix the fan “outside” the cart (=below the “cart cage” as you did it now) is a better idea than to put it in the “cage” – the iron bars of the cart-cage are more obstrusive for the wind than one might think. I guess this is also the reason for the much better performance of the cart…
      What about the scooter? any news there? I am building one as well…a bit bigger than yours, bigger tires, aluminum chassis, but similar as yours it is a “stand on” rather than a “sit on” version…I am alwasys very curious about the stuff that you are building, very well done things and even better ideas ;)
      Martin

    10. Mike L Says:

      Thanks chuck, im getting the 3mm htd, 5mm bore, 12 tooth pulley, with fairloc hub so i dont need to do any grinding. Im using it with the turnigy aerodriveXP SK 42-60 500Kv, it should double the torque and triple the speed to 30mph.

    11. the chuxxor Says:

      For any EV use, I’d strongly recommend one of the rotor bearing endowed Turnigy motors, such as the 63/64 Aerodrive.