How To: Super Cub Aileron Mod

Posted on October 6, 2007 by Dan

I got a new radio last week and decided to retrofit my Super Cub with a couple of 3-wire servos and add ailerons. I pulled the servos out of my Mini LST truck and my RC18T. I don’t know what kind the MLST ones are, they are pretty small, smaller than my HS-81MG, about 0.9″ x 0.9″ and probably about the size of the HS-55 servos. But they work perfectly for ailerons. I fixed the rudder with the stock servo, and installed the HS-81 for the elevator. If I had another servo, I would also run the rudder, but for now it’s just fixed and flies just fine without it.

I measured and cut the ailerons with a razor blade 12″ x 1.75″ with the inside edge 7″ away from the center of the wing. I bought a set of replacement control horns for the SC and installed them in each of the ailerons (the same ones that go into the rudder and elevator). The pushrods are 0.047″ diameter steel which I just bent into a “S” in each end and fit into each of the control arms and servo horns. There is no mechanical adjustment this way, so I just made sure that the servos were dead center with the trims on the radio at +/- 0 and then bent the ends just perfectly. I messed up one, so I just redid it and then with my radio I dialed in each servo so they were completely flush.

I used tape for the aileron hinges which as far as I can tell is simple, effective, and works great. When cutting away the notch for the aileron to rotate up/down, make sure you do it in the underside of wing and not the top-side of the wing or in the aileron. You want to maintain a nice smooth airframe on the top of the wing. I cut cutouts in each wing just the size of each servo and taped over them to hold them in place. Each servo runs to its own channel on the radio, and then I use a setting called Flaperon. With the switch down, I’m in normal aileron mode where each aileron opposes the other at all times. Then I can flip the Flaps switch up and both ailerons are thrown down, perfect for making great landings and takeoffs. Let’s see a single servo aileron setup do that! This also allows me to fine tune each aileron since I don’t have any mechanical adjustment in this area. This new radio is sweet, it can do so much. It’s a Futaba 6EXP by the way. I plan on doing a write-up on it later, but my first impressions are this is a great radio.

After I got everything installed and the ailerons working, I was testing it out when all of a sudden the stock 480 motor just died. I tried running straight off a couple of volts and it was just dead. So I did a quick replacement with my old Speed 480 BB Race motor. Though my past experience suggests this isn’t a great motor for the SC, I had to give it a shot because I wanted to try out my cool aileron mod.

And so this morning the wind was calm so I took her out for her first flight with the new radio, ailerons, new ESC, and the new Speed 480 motor. I checked all my trims, checked for proper movement of everything and gave her a throw. I quickly realized that my elevator servo was reversed – up was down and down was up. Ooops! I was so busy making sure that the ailerons were moving properly that I completely overlooked making sure the elevator was moving properly. I made an attempt to land while instantly trying to retrain myself and not throw the plane straight into the ground. I managed to bring it sound safely thinking to myself how did I miss that?? I reprogrammed my radio and a minute later had the elevator moving up and down properly as it should. At least it was turning left and right the way it should. So I gave it another toss and she flew perfectly. The plane definitely handles differently without the rudder. The plane gets sideways really easily when turning but still handles great. I’ve been practicing my barrel rolls, which though this plane can do, it’s doesn’t do them very well. The new motor lacks much power, so the plane feels kinds slow, but the ailerons work great and it feels like a completely new plane and it’s still very easy to fly. Now I just need to work on my power options, maybe go brushless?

So here’s a few pics and some video.

ailerons1.jpg ailerons2.jpg ailerons4.jpg ailerons3.jpg ailerons5.jpg ailerons7.jpg

Posted in R/C Planes | 1 Comment

DIY In-wall RS Speakers and R/C Stuff

Posted on September 30, 2007 by Dan

A couple years ago I came up with an idea on how to build a really cool in-wall speaker system that allowed the end-user to install any raw driver-tweeter combo they could imagine. Then, to my surprise, Parts Express began offering the exact same thing, which they call the In-wall Mounting System. With the concepts being identical, I can’t help but kick myself for not trying to get my idea into the marketplace sooner. At any rate, I’ve decided to pick up a set of (3) of the IMS-711 mounting systems to build into a set of 2-way speakers for my master suite making up the Left-Center-Right channels of a new Bedroom Home Theater. The speakers will consist of Dayton’s Reference Series 6″ Aluminum cone woofer and their 1″ Dome Tweeter. Both drivers offer excellent performance at a reasonable price and to my knowledge, no one has built these drivers into an in-wall, yet. I bought a set of these speakers last year with the intent to rebuild a small pair of bookshelf speakers. Well the project never really took off, and I’ve been trying to figure out what to do with these drivers ever since. I’ve got a cheap 27″ LCD HDTV mounted on the wall now with just a DVD/VCR combo connected to it. The plan will be to upgrade to a 32″ or 37″ LCD in the near future, but now I want to get in the new in-walls and a decent 5.1 channel receiver. For the sub I’m debating on trying out the new 8″ RS sub from Parts Express as well in a small ported box with a 250W amp. All I need is something small and inconspicuous to fill in the low end. It looks like a great little sub and could be a lot of fun to build into a system.

Anyway, so that’s it for now. On another note, I’m getting a new Futaba radio to satisfy my R/C plane addiction that recently has kicked in again. I’m still getting a lot of great flying time out of my Super Cub. It’s been a really great first plane, but I’m anxious for something more. I recently discovered that a friend of mine who lives in my same neighborhood is actually into R/C planes and flying. He builds planes from scratch and has this super-cool 22″ wing that just screams. So I’ve been looking into getting a flying wing, these things are insane, and can do crazy spins and soar as fast as 90 mph. It might be a bit much for a second plane, but they look like a lot of fun. The one I’ve been checking out is the SpeedWing 250 MkIII. It looks like one of the better setups out there, and you can go brushless for as little as $50. But getting a new plane means getting a new radio, so that’s the first step. Tower Hobbies has the Futaba 6EXP which just came out for $129 which as far as I can tell, should suit my needs for a long time no matter which plane I plan on getting. Should be fun, the hardest part though is deciding what to spend money on first, the speaker stuff or the R/C stuff. Decisions, decisions…

inwalls.jpg
sw250mk3_720×418.jpg

Posted in DIY Audio, R/C Planes | Tagged , , | 1 Comment

RC18T Running a 10-Turn 540 Motor and 3S Li-po

Posted on August 1, 2007 by Dan

3s10t540-1.jpgAfter I installed a stock 27T 540 motor into my RC18T, I quickly became addicted to the speed and power that this little truck could dish out. Soon after, the 2S 7.4V li-po battery I was using to power that stock motor didn’t feel quite so fast, so I upped the ante to a 3S 11.1V li-po with the same 27T stock motor. Now things were cooking. The truck could not be stopped, and the top speed was measured at just under 50MPH. But the car was still controllable, so I knew it could handle more speed. So this past weekend I pulled out the stock 27T motor and replaced it with a Trinity D6-series 10T single round-wire motor and then kept the same 3S li-po battery. Yeah, this is going to book. I had to replace my MC230CR ESC since it’s only rate for a 20T+ motor. So the Novak GT7 I have definitely fit the bill touting a 5T motor limit at 7.2V. Well, I’m running 11.1V, just a wee bit above what it (and the motor) are actually rated for. But for a few quick runs up and down the street shouldn’t be too much to handle.

In a nutshell, this thing is quick, amazingly quick. Now we’re to the point of out of control, as I can barely keep on the throttle for more than a second or two before the truck is all the way down the street. Though I haven’t measured the top speed, it’s got to be around the 60MPH region, since it’s much quick than the stock motor which clocked in at just over 47MPH. I’ve got it geared with a 25/60 pinion/spur combo and it feels perfect. I’ve got enough torque to being flying down the street at half throttle, about 20MPH or so, and then I can punch it and it will literally pick the front tires up off the ground and flip over over onto its shell, and this is not from a stop, or on carpet. The smallest pinion that would fit before the large can of the motor hits the center drive shaft is probably about a 23-tooth. The largest pinion that could fit is only limited by what’s available in a 48-pitch, which is a 36T made by RRP. Thought gearing that high would put a lot of stress on the battery, ESC and motor, and although could reach some insane top speeds, probably wouldn’t be practical for everyday driving around.

The biggest problem I’ve encountered so far is stripping the input gears and differential gears. I’m on my second set right now. I’ve basically had to resort to street-only driving, since driving around in the dirt fills the gearboxes with dirt and rocks, which then leads to the two gears inside wearing out much quicker. The plastic housings don’t do a very good job keeping things tight either, even though the diff is shimmed about as tight as you’d want. The housing and the gears need to be made of aluminum, Delrin, or even better, steel. I’ve lost all the springs that go into the output shafts, and had to replace them with springs from ball-point pens. Which works perfectly, thank goodness for small favors. I’d also like to get an aluminum spur gear. But the rest of the truck is pretty bullet proof. I’ve taken some nasty spills where the truck just flips end over end for hundreds of feet and it just keeps going. I haven’t taken it off jumps, and I’m extremely easy on the throttle, so I am babying it so it will last. One crash threw the li-po out of the truck and another ripped the 540 motor mount off. So it isn’t without its problems, but when it’s not running, I’m having fun sitting the workbench in the garage fixing it, tweaking it, making it more robust, and trying to come up with ways to make it just work better.

I wanted to say thanks to Chris C. for painting such a sweet body and sending it to me. Thanks Chris!

Visit my web page dedicated to the RC18T!

3s10t540-2_small.jpg
3s10t540-3_small.jpg

Posted in R/C Cars | 2 Comments

18dB Crossover for MTM Home Theater Speakers

Posted on July 7, 2007 by Dan

I found some time today to build up the crossovers for my friend’s new home theater speakers. I am by no means an expert on custom crossover design, and the small array of free tools I have at my disposal are all I know to design a better-than-textbook crossover for a pair of loudspeakers. It is probably the most complicated aspect of DIY speaker design, the least understood, and the most affecting of how a speaker will sound in the end. Even enclosure design takes a backseat to the criticality of crossover design. Just about anyone can build a box and toss in a port and be happy with the results. And most people do exactly this (myself included) using techniques that are basically textbook enclosure design. Lucky for most of us DIY’ers, textbook enclosures are amazingly accurate and perform almost exactly as modeled or simulated. But crossover design is an entirely different animal, one I am just barely trying to tame, one speaker project at a time.

This is basically how I designed this crossover: I started with the drivers; in this case a pair of 7″ Dayton aluminum cone woofers and a Morel MDT-20 soft dome tweeter in an MTM configuration. PE offers CLIO plots of the Dayton woofer for both impedance, phase, and frequency response which is great, it takes one less step out of the process. Since there are no data files for the Morel tweeter, I had to rely on capturing the data a different way, and that’s by using SPL Trace. With just a picture of the FR and impedance of the tweeter, I generated data which was then imported into a crossover program, along with the woofers.

So what’s the best free tool for designing crossovers? My favorite is Passive Crossover Designer available from the guys over at FRD Consortium. I loaded the impedance plots and FR plots into PCD and just started tweaking around. For these speakers I started with a x-over point of 1.8kHz and then hit Initialize Textbook values just to get a starting or reference point. Then from there I like to move things around just a bit until the combined summation response look as flat as possible. I tweaked around with the values for about 2 weeks before finally coming up with the final crossover values. Even these are probably not ideal, and the combination of possibilities is quite numerous.

The final crossover turned out to be pretty much a textbook 18dB/octave Butterworth crossover for the high-pass section right at about 1.9kHZ (with no padding) with a slight tweak on the inductor to flatten out the FR a little. The low-pass section started out as textbook but I ended up with a much larger shunt capacitor. I’ve found that in a lot of cases the cap required on the woofer must be a lot bigger to help roll off the cone break up modes quicker. Also the addition of the series 0.20mH inductor helps drop the cone’s break-up modes even lower without altering the crossover point, and thus providing the 18dB/octave Butterworth slope. The Zobel network is also basically a textbook Zobel with a 25uF cap in series with a 4 ohm resistor and wired in parallel across both woofers. The schematic is shown below. Very simple, nothing fancy with standard values which are easily available for purchase.

So I’ll update with more details and measured results of these crossovers. As of this writing the speakers have actually been installed in my friend’s home theater and we’ve already watched bits and pieces of a few different movies and they sounds fantastic. We were both really happy with the overall sound. But more on that later! So this is it, the crossovers completed.

Read the whole story here.

Crossover Schematic
jamins18db_small.gif

Summed Frequency Response Plots from PCD 3.00
summedresponse_small.gif

Completed Crossovers using Dayton Caps and Jantzen Inductors on 1/8″ Board
18dbcrossovers_small.jpg

Posted in DIY Audio | Tagged , , , , , , , , , , , | Leave a comment

2,000 Watt 15″ TC Sounds TC-3000 Sub Project

Posted on June 26, 2007 by Dan

Well I’ve started designing another massive subwoofer for a friend at work. We started talking about audio and speakers a few months back when he’d mentioned he was looking to buy a new sub for his up-and-coming home theater. So of course I chimed in and said, “Hey, let me design one for you.” So we kicked around the idea for a few months, and watched the deals and sales over at TC Sounds come and go. Then finally this past weekend he dropped off a receipt on my desk showing he’d just paid for one 15″ TC-3000 Subwoofer. Nice. And so the project has officially began.

After running some simulations in Unibox 4.07, we’ve basically decided to go with a standard QB3, 4th order alignment which requires a 6.0 cu.ft. (170L) box tuned to 20Hz. This yields a -3dB point of 19Hz and a very flat frequency response pretty much all the way down to 21Hz. The question may arise, why not tune lower (EBS)and sacrifice some upper/mid bass performance for some crazy bass into the teens? Well two reasons – box size and port length. What I’ve modeled so far with the 170L enclosure, we’re looking at two (2) 6″ ports which are 58″ long each. Ports that big and that long take up a whopping 2.2 cu.ft. (63L) of space inside the enclosure. To drop the tuning frequency 1Hz requires each port be an extra 6″ long. To drop 2Hz requires 14″ extra inches. And to drop 3Hz, to a tuning of 17Hz, would require each port to be 24″ longer. Seeing a pattern here? I have yet to figure out how I’m even going to fit the two 6″ ports into this box that are long enough to tune it to 20Hz, let alone tune it much lower, but I’ve got some ideas. Besides 20Hz models well in this size enclosure with no hump or drop in Fr. If we have to, we can use just one (1) 6″ port, but the port noise is going to be on the high-side. That’s why the whole port situation is still up for debate. The size of the box is already getting big, so I don’t want to have to change that too much, but the ports…we’ll just have to see.

The second thing I’ve been looking at is the amp to drive this sub. Now where can we get enough cheap power to drive a sub of this magnitude? From reading around and checking out a few places, the Behringer EP2500 is a very popular amp with the DIY crowd and is capable of pushing just about 2kW of real-world power into a single bridged 4 ohm load. That sounds like it should just about do it. And for a price of only $349, it’s probably the most bang-for-buck you can buy. And Parts Express carries it too which is nice, since I like buying all my speakers from them. Well with the exception of the TC Sounds sub, but for just about everything else…it’s PE all the way.

And so the project design phase has begun. I’ll be update this blog as well as Audio Innovation with the details of this build-up, but it should be fun and at if nothing else, give me something to write about.

tc3000_small.jpg
ep2500.jpgvb-response-tc-sounds-tc3000_small.gif

Posted in General | Leave a comment

E1505 Sound Card and Speaker Performance Results

Posted on June 26, 2007 by Dan

Ever wondered just how good that cheap sound card in your laptop is? How about those tiny little speakers that sound more like a pair of headphones coming from someone’s nearby iPod? Well I’ve been hooked on this great tool called Room EQ Wizard (which is actually used to measure room modes and generate EQ profiles to combat them) but it’s got some other great uses as well, if used in the near-field, like measuring the frequency response of a new set of speakers or measuring the flatness and harmonic distortion of a sound card in a PC or laptop. So I put my new Inspiron E1505 to the test, and here are the results. Overall this is an excellent sound card and is very flat across most of the audible spectrum, see Figure 1. The 20Hz – 20kHz flatness is measured at -1.7dB, +0.8. Also, the 1st and 2nd harmonic distortion came in at 0.015% and <0.001% respectively. The -3dB points measured in at 14.3Hz and 20.497kHz. If you plugged this laptop into a stereo or receiver for playing MP3's, you'd probably never notice the +0.8dB peaks in the upper band or the 1.7dB drop at 20Hz. But it's definitely not quite as good as a real CD/DVD player's line out however. So how do the integrated speakers fair? Well with the exception of providing any bass at all, see Figure 2, they are also extremely flat within their passband with no wild dips or peaks. Above 10kHz you start to see some peaks and valleys but overall they are pretty flat. The speakers in the E1505 are basically good down to about 300Hz where the response drops off like a rock. So even though the bass isn't all that impressive, quite pitiful actually, where it makes up for it is flatness across the usable range of the speakers, which is about 300-20kHz. And they do actually sound quite good, and play plenty loud for just about any occasion. Figure 1. SigmaTel Audio Inspiron E1505 Frequency Response e1505-sigmatel-audio-fr-plot.jpg

e1505_small.jpg
Figure 2. Measured Frequency Response of Left and Right Speakers

Posted in General | Leave a comment