polyfractal's blog View Details
Posted by polyfractal | Nov 17, 2012 @ 11:40 AM | 2,082 Views
Quick update about CompareRC: I finally integrated Amazon search results into the product listings! If you want to check it out, a product like the "Spektrum MR3000 Marine 2.4GHz 3-Channel Receiver" is a good example of how it is supposed to work.

It's taken a while because Amazon's API is a bit unwieldy to use. Because of the way Amazon has structured their API, results from Amazon will only show up on product pages and not in general search.

So what this means is if Amazon carries a product that I don't have indexed from another vendor, it won't show up on the main search page. But if you click a product carried by a vendor in my index, it'll search Amazon for the same product.

I'm working on full Amazon integration and should have the products showing up in the main search results soon. As usual, I'd love to hear comments or complaints about the site!
Posted by polyfractal | Nov 03, 2012 @ 09:13 PM | 2,487 Views
Spent today rewiring parts of my Sky Surfer and moving components around. The main reason was prompted by sporadic GPS signal loss. I've never had a great GPS signal (EzOSD takes a considerably time trying to find satellites, and I've gone under 6 satellites while flying once or twice).

ImmersionRC's troubleshooting guide says this is almost always due to RF interference. I have my EzOSD mounted in the center of the fuselage, between the VTx and the Rx. Importantly, the power line for the VTx runs right by the sensitive GPS unit.

So today's project was to break out the GPS unit so it was far away from unshielded cables. I used the provided extension cable and re-routed the GPS to the top fuselage. I feel much happier about this arrangement. I'm a little concerned about the extension cable, since it runs right by the motor cables. I'll have to see how bad the interference is. I may need to shield the extension cable. I should probably just replace all my wires with shielded equivalents...but I haven't found the motivation yet.

While I was reconfiguring things, I decided the cockpit was too damn cramped and difficult to service. I previously had the camera in the cockpit foam insert. Instead, I cut a small hole in the nose and placed the camera there. I also replaced the foam cockpit with a little foam platform that the Rx is velcroed to.

Everything is much cleaner now. I'm very happy about the new layout...will take it out flying tomorrow to see how it all performs
Posted by polyfractal | Oct 27, 2012 @ 08:52 PM | 2,452 Views
It was pretty rainy today so I got a lot of work done on Dragnipur. Check out the build log if you want more details on what's going on. It's been quite the saga so far!

Posted by polyfractal | Oct 21, 2012 @ 09:55 AM | 2,221 Views
My second successful* FPV flight, first that I've been able to record. Mostly just just puttering around a big field, so I made sure the video was short. I mostly just wanted to share how my dog chases after the plane like a lunatic. Does anyone else have dogs that do this?

Second FPV Flight - Leisurely Laps around the field (3 min 17 sec)

*I've flown a few more FPV flights, but the other ones ended in calamity for a variety of misconfiguration problems. This is only the second time that nothing horrible has gone wrong =)
Posted by polyfractal | Oct 18, 2012 @ 07:27 AM | 3,698 Views
Having never built a plane before, I decided it would be fun to scratchbuild a foamie using Dollar Tree foam boards. I wanted to work on something different...not your standard straight-wing glider or swept flying wing. I stumbled on a design of the Pioneer III and thought it was a pretty slick looking plane. I decided to use it as inspiration.

So I started to doodle various, related designs. Eventually, I ended up with this. It's something like a reversed flying wing. Straight leading edge, tapered trailing edge. Cambered body, two vertical stabilizers. Pusher prop for thrust. Simple elevons for control surfaces. Maybe rudders? Probably not though. There will be a pod that attaches to the underside for electronics and (hopefully) FPV/camera gear.

I'll be documenting most of the build progress in this thread over at the Scratchbuilt Forum, but I'll post occasional pictures to my blog too

Wish me luck! Or tell me what I'm doing horribly wrong!
Posted by polyfractal | Oct 16, 2012 @ 03:35 PM | 3,143 Views
I'm not really a car guy, but I thoroughly enjoyed this video. It has everything - cars sliding around corners, cop cars doing flips, driving through fruit stands. Hilarious.

Note: NOT my video, just found it on youtube.

The Greatest R/C Car Chase Ever (2 min 28 sec)

Illegal street racers take on the law in the world's most intense police chase! Sort of.

Special thanks to Rob and Big as well as the Need for Speed: Most Wanted team for making this video possible! The game comes out on 10/30, and it's made by Criterion, aka dudes who know what racing games are all about. Check out the trailer!

Sound design by the dude who did sound design on the game itself Byron Bullock. Music by John Robert Matz

Posted by polyfractal | Oct 15, 2012 @ 11:21 AM | 2,863 Views
In my free time, I've been building CompareRC, a search engine dedicated to the RC hobby. Since I'm just doing this for fun...I'm the only one working to improve the site. There are lots of things that aren't working great, so I need to prioritize my time.

Would you mind giving some feedback?

Head over to this thread
where I posted a poll about what's broken, what needs fixing, etc. Your input is appreciated...I really want CompareRC to be useful to the RC community!
Posted by polyfractal | Oct 14, 2012 @ 04:14 PM | 2,808 Views
Yeah, yeah yeah. Everyone says “Learn how to fly RC first!” before adding FPV gear. It makes sense – you don’t want to crash a few hundred dollars of expensive video equipment into the ground. I’ve been doing a fair amount of crashing, so I can totally understand this position

Then again, everyone also says that flying FPV is totally different from flying LOS. Using that as an excuse, I embarked on adding my FPV gear to my Sky Surfer. My rationale is that I’m confident enough in flying the plane that I won’t crash immediately, and that I have the plane pretty well trimmed out. Considering that FPV is a lot different from LOS, this seems as good of time as any.

And let's be honest...I'm just being impatient and this is a good enough rationalization to start FPV

I’m using the Custom Goggles 5.8Ghz starter package from ReadyMadeRC, which includes the Fatshark Predators, an ImmersionRC 600mW video transmitter, Bluebeam cloverleaf/spw antennas, a 700 line NTSC camera and all the associated wiring needed to rig it up. I also have an ImmersionRC EzOSD, but I won’t be installing that yet.

I don’t have a canopy platform, so I’m just going to hack a hole into the foam canopy. Bonus points because it will help cushion the camera in event of crash landings.

I chose the mount the video transmitter in the tail, so that it was as far away from the radio receiver as possible. To do this, I cut a small hole in...Continue Reading
Posted by polyfractal | Oct 11, 2012 @ 08:22 AM | 3,088 Views
This feature has been a long time in the making - CompareRC has been upgraded with category search and browsing.

If you are unfamiliar with CompareRC, it is a search engine tailor-made for the RC community. I've been building it in my freetime, outside my normal day job as a software engineer. To date, I have indexed over 30 vendors and nearly 200,000 individual products.

One of the most often requested feature was the ability to browse or search in certain categories. This has been difficult to implement since each vendor categorizes their products differently (and some don't have categories at all). It has been a long battle trying to reconcile these differences. Computer algorithms help...but a lot of the work has been manually sorting parts into various categories.

I'm still not done - a lot of products remain uncategorized. I have a few ideas to speed this up. Possibly a contest where RCgroupers categorize parts, with a $100 gift-certificate going to whoever does the most?
Posted by polyfractal | Oct 09, 2012 @ 08:28 PM | 3,090 Views
My Sky Surfer has been banking heavily to the right. At first, I thought that I had the control rods setup poorly. However, after landing and verifying that the control surfaces were, in fact, level I began to think it was something else. The banking is so bad that my ailerons are completely trimmed to one side...and that just barely counteracts the bank. It still drifts to a side.

After reading dozens of posts in the Sky Surfer thread I found someone talking about a similar problem. Turns out my tail feathers were bent! Relative to the wings, they were slanted to the side.

I glued the tail feathers on, but luckily it was easy to shove a carbon fiber rod through the fuselage and glue it to the feathers. After drying I took it back out and ta da! Flies nice and straight!

While I was mucking around, I also re-configured the control rod holding the rudder. Before, I had a simple "L" bend connecting to the control horn. I noticed this slipped occasionally and didn't want it to come off mid-flight. Reconfigured to use this kinked shape...much better

Posted by polyfractal | Oct 05, 2012 @ 08:49 AM | 3,054 Views
Followup to my last blog post, here is the flying-wing but without the winglets. Same conditions (head on wind, 25 m/s which is roughly 55 mph). Interesting to see the differences.

I wish I would have made the simulation boundaries a bit larger, it looks like there are some wingtip vortices just outside the boundary. I expected them to be closer to the wing tip.

Apologies about video quality, I'm working to improve it. My computer has a hard time running the simulation and recording at the same time...and then youtube butchers the quality some more

Airflow over a Flying Wing (3 min 15 sec)

Posted by polyfractal | Oct 04, 2012 @ 08:56 PM | 3,027 Views
I dearly love my Sky Surfer platform – I’d fly it every day if I could. Unfortunately, the weather does not always cooperate. Or those pesky things called responsibilities such as taking the dog to the park, taking out the trash, making dinner, etc etc. I'm sure everyone knows the feeling

Luckily, there are always plenty of activities to kill time in between other activities. Today, I started toying around with a really fun piece of software by Autodesk called Project Falcon. It is a computational fluid dynamics modelling package…basically software which simulates airflow. There are tons of great software out there to accomplish this, but they all require some serious knowledge of computational modeling and aeronautical engineering.

Falcon is basically “baby’s first CFD”. It’s very easy to toss a model in and start tweaking Wind Tunnel parameters.

I've been eyeing scratch-built foamie flying wings for a while. I've also been entranced with the "C-Wing" design, which adds horizontal winglets on top of vertical winglets. There are two primary advantages. First, the c-configuration reduces drag due to vortex formation behind the wing, similar to a completely closed wing (like a circle or box wing). The second advantage is to eliminate the need for washout on a swept wing. The winglets help to act as wing-fences, reducing the amount of spanwise flow. The upper portion of the winglets also exert downward force, providing pitch stability.

At least, I think so. In any case, I built a crude C-Wing in Sketchup and loaded it into Falcon, with the following results (make sure you go full-screen, the weird aspect ratio makes it hard to see details otherwise):

Airflow simulation of a C-Wing flying wing (4 min 23 sec)

You can definitely see spanwise flow sliding laterally across the wing, as well as vortices behind the c-winglet configuration. The airflow is head on...my next simulation will be using some angle of attack. I'd also like to model a regular flying wing to see how it compares.
Posted by polyfractal | Sep 26, 2012 @ 10:28 AM | 3,197 Views
Over the weekend, I took my Sky Surfer out to a local green space for her first, maiden flight. The area was down close to the ocean, so there was a strong breeze...that should have been my first warning sign. This was also the first time I've ever flown an RC plane, so that really should have been the second sign that bad things were to come

No matter how much you read about flying a plane, nothing really prepares you for that first flight. It lasted about 5 seconds and was pure terror. Nose-bombed straight into the ground, but not too much damage.

Second flight, 15 seconds of anxiety, pile-drived the ground again. A bit more damage, the side of the cockpit fuselage was starting to buckle.

Third flight, about 30 seconds of excitement...it was still in the air! Then I got too ambitious and tried to turn and, you guessed it, straight into the ground. Alas, this was one crash too many for my poor plane:

I packed up and headed home with a head full of thoughts. From my little adventure, this is what I learned:

Fly in a larger field
The area I was flying in was too small. I underestimated how quickly the plane eats up ground. After just a few seconds it was racing towards the edges of the field and I desperately didn't want to lose it
Fly with more altitude
Because I was flying in such a small area, I was afraid to take the plane up very high because I didn't want to lose it. Unfortunately, I discovered the hard way that low altitude means you have no time to correct mistakes. Anything that goes wrong...goes into the ground
Flying is not like driving
When you turn a car, you keep the wheel turned until you are done, then straighten out the wheel. I probably should have known this ahead of time, but you don't hold the stick in position. All three crashes were because I held the ailerons to the side in an attempt to straighten, causing a roll into the ground.

Lesson learned: move stick and then back to neutral.
Foam is easily repaired

Nothing a little gorilla glue and duct tape can't fix

Posted by polyfractal | Sep 23, 2012 @ 05:29 PM | 2,950 Views
Added a few more modifications to my Sky Surfer, and then took her out for a maiden flight on Saturday. The last mods I added were:
  • Reinforced wing spar
  • Carbon Fiber rod along the fuselage
  • Swapped Deans connector for XT-60s
  • Moved the ESC outside of the plane
  • New 6x4 APC prop
I reinforced the wing spar by inserting an extra 0.188 24 inch CF tube. It was a really snug fit and got stuck a few times. A little WD-40 and gentle pounding from a hammer got it fully inserted. Much stiffer now, I can see why this is a recommendation.

The other bit of "common mods" seems to reinforce the fuselage, so I added a 0.125 CF tube along the fuselage. I'm not really sure how much this helps, it seems pretty flimsy. But the masters recommend it as well, and who am I to disagree

I noticed several people talking about how hot the stock ESC gets, so I went ahead and moved mine outside the plane. Dug a little pod for it to snuggle in to, and secured it with velcro. A bit ugly but functional.

While I was on a buying spree, I grabbed a 6x4 APC prop (although accidentally got the pack with 6 blades. Whoops). I purchased a prop adapter too, but was unable to get the stock one off. Instead, I slowly reamed out the 6x4's hole with a pair of scissors, slowly grating away plastic from both sides, testing, grating, testing, etc etc.

Lastly, I cut off the Deans connector and replaced it with an XT-60. I had previously ordered a bunch of 1800mah Turnigy batteries from...Continue Reading
Posted by polyfractal | Sep 23, 2012 @ 09:37 AM | 3,022 Views
The day has finally arrived: my Sky Surfer has shown up in the mail. I've been reading and dreaming about RC planes for months now. I finally pulled the trigger and purchased my gear...but it was on backorder.

Fast-forward a month and everything finally ships. I felt like a kid on Christmas, unwrapping all the gear. I also ordered a bunch of FPV gear, but it isn't allowed near my plane until I can fly it successfully.

My kitw as an RTF Sky Surfer. While technically ready to fly, I wanted to add some of the modifications that are often suggested. So, two modifications to get things started:
  • Hooks for rubber-bands on the wings
  • DuBro control horn replacements

Rubber band mod went smoothly. Hooks were attached with CA super glue and feels rock solid.

DuBro control horn replacement...not so smooth. I removed the old horns and glued the new ones into place. Then I read the directions and realized that these DuBro horns have little plastic plates that go on the opposite side of the wing, held together with pins.

Whoops. I frantically pushed the pins through and screwed them in. Luckily, I glued everything with Gorilla Glue so it was still curing. Unfortunately, the horns are now bolted and glued. If I ever have to take them off, it is going to be hell.

The second problem relates to the pin that holds the control rod/wire for the rudder and elevator. Apparently the holes in the DuBro horns are smaller than the stock horns, so the pin does not rotate freely (or at all). I don't have a drill so I couldn't drill the hole out. Twenty minutes of trying to enlarge the hole with a variety of tools (screwdriver, sandpaper, knife) was largely unsuccessful.

I opted to just bend the control wire, similar to the ailerons. Not a great solution and I'll probably have to fix them later.