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-   -   Building the Slofly EPP 28" Mini 3D (https://www.wattflyer.com/forums/showthread.php?t=2601)

timocharis 11-24-2005 02:26 PM

Building the Slofly EPP 28" Mini 3D
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There's no better way to learn 3D than with an EPP plane. Just learning a basic hover is guaranteed to produce crash after crash after crash. If you want more air time and less build time, EPP is the way to go.

However, because not much sticks to it, and it's very flexible, building with EPP can be a challenge until you know a few tricks. Once you do, it's easier than just about any other material.

When it comes to EPP planes, slofly.com is clearly the most bang for your buck. The two planes in the current lineup, one with a 22" span and the other 28", are usually priced between $15-20 each. There's almost always a twofer deal going, usually something in the range of $30 for two. You should take advantage of the deal, since you'll undoubtedly dislike something about your first build and wish you could make it "o so better." Not to mention the fun of getting a black one and a white one, then mix'n'matching the parts.

EPP is a learning curve, but fortunately a cheap one. In this thread I'll try to take some of the slope off that curve.

My techniques are far from the final word on this subject. Many of the approaches I take are simple preferences -- EPP is pretty forgiving, so lots of different approaches will lead to good results. However, so the curious builder won't have to wade through the usual collection of "here's my goofy plane" pix and "you're an idiot Dave" postings, I'm writing this entirely ahead of time and will try to post it all as one lump.

I hope some of the other skilled builders, especially Steve, Gene, Tony, Rick, Lloyd and others will chime in with their own prejudices and tips at the end. With any luck, the signal-to-noise will remain high.

It's also a good idea to check out the official build instructions, which you can download at http://slofly.com/howto/ -- look near the bottom for the 28" pdf file. Though the manufacturer takes a significantly different approach to the build than I do, I'm sure it would work just fine. You may see something there you like better than my approach, and if so, go for it! These planes are cheap, and they practically scream out to be experimented with.

So what do you get for your $15-20?

timocharis 11-24-2005 02:27 PM

You Get Seven Piece Of Foam
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Fuse, wing, stab, elevator, rudder, ailerons. Precut and ready to assemble. That's almost it -- Steve Bobich (the owner) usually tosses in some scrap so you can make useful mods, some of which I will suggest. That's why the kit is so cheap.

To finish you'll need glue, tape, and some kind of carbon fiber (plus electronics). It will come as no big surprise that you can also buy those from slofly.com. You may also wish to use some paint, markers, inks, dies, or whatever to decorate. It is neither reasonable nor necessary to cover these planes, so I'm sure some people do.

Assuming you have some glue and tape lying around, the actual plane will only require some carbon. If you use my approach, that will probably set you back another $6 and you'll have some left over.

For building the plane I used:
3 rods of 1mm carbon fiber
Canopy Glue
Both Thick and Thin CA
EPP Hinge Tape (special strapping tape Steve sells)
Slofly Motor Mount
Du-bro Mini Hinges
Four GWS control horns

For electronics I used:
LensRC 20-turn 22.7mm CDROM motor
Two GWS Pico servos
One HE-540 servo (ailerons -- later switched out for an Eflite 7.5g)
GWS R4P-II Receiver
E^3 M-72 Base-loaded antenna
Castle Creations Phoenix 10 ESC

I wanted to use the newer Cirrus 4-gram servo for the rudder, but it blew out during assembly (I have no idea why. Simply stopped working). I planned to use a 5-gram Cirrus servo for the elevator, but it was so sloppy I couldn't stand it (and it jumped at one end of the travel). Needless to say, I'm done with Cirrus.

The HE-540 is discontinued, of course, since it was the finest small servo ever made. At 5.7 grams in a very small case, it delivers over 15oz torque in .08 seconds over 60 degrees. Nothing else I know of comes close.

Total airframe weight is 5.1oz. Flying weight is 5.9-7.0oz depending on battery.

timocharis 11-24-2005 02:28 PM

Fit, Trim and Plan
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When your plane arrives, the ailerons should be masking-taped to the wings and the elevator to the stab. Inspect the surfaces of each, and decide which one looks better. If you're like me, you'll want that to be the "UP" side. Tear off some tabs of masking tape and mark the left and right ailerons on their top sides. Mark the top of the wing "up." Mark the stab and elevator "UP" sides.

This is actually an important step. EPP is not precise stuff, so when it gets cut, the resultant shapes should stay in the same orientation. This will give you the best match at final assembly.

Next, jam everything sorta where it's supposed to go. Get a feel for the weight and glue points. You should be able to figure out where the parts go all on your own... and don't forget to toss your plane -- at this point it will usually try to fly tail first.

Keep an eye out for things that don't fit or are not straight. This is also a good time to pull off any 'hairs' you see sticking to the EPP.

You may find the wing or stab a little thick for their slots (EPP is not always exactly the same thickness, even across a single sheet). If so, open up the slot now with some careful blade work or sand paper (wet/dry works great in 120 and 220 grit). Pay close attention to the front of the wing slot, and maybe even the motor slot.

Speaking of sand paper: the plane flies a little bit better if you round off the front of the wing (and perhaps the stab). This is a good time to do that. The best wing I've done starts with a blunt rounding like a parenthesis "(" near the root and ending sharp near the tip "<". I left these wings flat in front because I want to compare how it flies "stock." I'll round them later.

Also, think about how you want the control surfaces to hinge. You'll want to be ready for the next step.

Almost certainly, the back of the fuse won't match up. Use the squares on your cutting board (or whatever) to figure out the right line, and trim it. Getting that straight "during manufacturing" is difficult.

Don't toss out the excess trim. It's exactly the right width to use as a plug for the slice to the elevator cutout. Some part of it will probably match exactly when the time comes.

timocharis 11-24-2005 02:29 PM

Let's Get Started
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Time to bevel your control surfaces. You'll need a very sharp x-acto knife (new blade) and a straight edge of some sort. A steel rule is ideal. Make sure you have the orientation right: for example, you want to place the bottom of the aileron up when cutting.

Make sure you look down on the surface from directly above, and that a little bit of your ruler or guide edge is showing. Otherwise you might not end up with a straight cut because the blade creeps past the corner. On the other hand, if this does happen it's not very important. EPP is very forgiving, and all will be fine in the end. In fact, it's so hard to hold the mooshy stuff in place that you'll probably get a little bit of error no matter how careful you are. Don't panic.

The elevator is a bit tricky, because you actually have several possible approaches. The easiest is to take a bevel on the top side of the elevator. You can get more adventurous and take the bevel from the stab instead, to get larger throws. Or you can do as I did, and use hinges (the elevator is a weird problem, and I prefer to hinge it for neutrality). In the last case, you bevel it like this: > (I put the bevel in the stab, not the elevator).

I took the bevel from the right side of the rudder. Here's the basic technique:

timocharis 11-24-2005 02:30 PM

The Carbon Supports
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I use 1mm carbon rod placed on each side of the wing and fuse, directly opposed. I first came across this technique building a Mini Weasel (alas, a discontinued plane last I checked). It's very light, cheap, easy and strong. Other people prefer ribbon (works well) or .125 tube (works well). The other techniques seem harder and heavier to me, so I take the easy way out.

On the wing, you should get about 1" from each end and about 1/4 of the total chord back. A little less is fine. For this build, I 'averaged' the chord in front of the aileron cut just for the fun of it (seems to work fine). It's not actually curved in the middle -- there's a straight stretch of about 1-3/4 inches, but the rod curves in its slit.

timocharis 11-24-2005 02:30 PM

Prepare the Blade
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To make the cut, mask your x-acto blade with some tape. A bit less than 2mm of the tip should be exposed. When you make your cuts, don't press hard. A couple of light passes should do. The object is to make a slit just barely deep enough to accept the rod. If it protrudes slightly, that's not a problem.

Here's a photo with the rod included for scale:

timocharis 11-24-2005 02:31 PM

Insert the Carbon
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Once you make the cut, you have two basic choices for installing the carbon. The classic method (which works fine and is easier) involves slipping the rods into the slots, then soaking lightly with thin CA. This make a more rigid part, but also more brittle.

I use a slightly more durable approach that's messy and annoying, which I will illustrate in tiresome detail. The idea is to first get some white glue (Canopy Glue is my preference) into the slot, then smoosh the rod in. Both steps are a bit sloppy.

Either way, the insert the carbon at one end and sort of roll it into the slot. Fiddle with it a while and you'll get the hang of it.

To get white glue into the slot, first put the wing or fuse on the edge of the table and bend it to open the slot up. Then in with the glue. It looks something like this:

timocharis 11-24-2005 02:32 PM

Carbonate the Fuse
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The fuse only uses up one rod since the distance you need to cover is fairly short, and less than half a rod will be enough on each side. Basically, you want to make sure one end is at least over the stab and the other as far past the wing/aileron joint as reasonable. Don't try to put it on the same level as the wing/stab slots -- put it slightly above so you can achieve this length.

(Special thanks to Lloyd Pound for pointing out this location as best. The idea is to make sure the fuse, stab and wing don't tear at their joints in the event of a bump. This saves quite a number of annoying little repairs down the line).

It's hard to get a picture that shows the whole length of the rod, but if you take a look at 'trimming the tail' back at the beginning, you'll also see one end of my rod.

Wait, what's it doing in that photo? Didn't you follow your own order of operations, Dave? Nope. Do as I say, not as I do.

The other end:

timocharis 11-24-2005 02:33 PM

The Stab/Elevator
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Theories abound on how this should be supported. Some think the rods should go in the elevator, others think the stab. Or both. I've tried them all without much difference one to the next. Both is safest.

My decision to use hinges on the elevator is primarily because I've done it before and like the results -- not because it's Really Important. I have also used tape with very good results, and don't think any one method clearly superior to any other. At least you get to see how hinges work -- they can also be used for the ailerons and rudder, if you wish.

First you need to decide where you want your hinges, then cut slots for them. I've used two DuBro Mini Hinges and one piece of CA hinge to stabilize the center.

After you've made the cuts, pump some glue into them. Not a heck of a lot -- just enough to make sure the entire 'pocket' is wet. That way, any overcut will be completely fixed when the hinge is glued in. To make sure you weren't too aggressive, pinch the slot to squeeze out any excess glue.

Here's what the glue application looks like:

timocharis 11-24-2005 02:33 PM

Finishing the Stab
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Next insert your hinges and slip the elevator onto the stab. Make sure you can get full play up and down -- if there's any constriction, just tug the hinges out a little and you can get more play.

Now cut your slots and insert the carbon rods. On the stab, I generally use CA rather than white glue to secure the rods. It's a short run, and rigidity is your friend on the elevator. Also, it seldom takes a hard knock (unlike the wing or fuse).

Bear in mind the stab/elevator assembly must be completely together before you put the elevator on -- you can't get back in without cutting and ripping a bit. That's one reason I like to get it done early on: so I won't forget.

timocharis 11-24-2005 02:34 PM

Prepare the Aileron Servo
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Another 'early do' is the aileron servo. It has to be ready before you put the wing in, because you won't easily be able to get at it. Remember: you also have to install the control arms and make sure they're centered. Of course, that will mean hooking up the receiver, esc and servo. Make sure your transmitter presets are all neutral at this time.

Wrap the servo in masking tape before gluing it in. This is a typical trick in foamy construction -- you'll probably want to reuse the electronics after you've beaten the plane to a pulp, and it comes out much cleaner when not covered by globs o glue.

Other tapes can work just fine (particularly blenderm), but overall masking tape seems to stick best. Good gluing surface. If you're picky about appearance, you can use a black sharpie on parts that might show.

timocharis 11-24-2005 02:35 PM

Install the Aileron Servo
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Unlike various goofyloose approaches, I put the servo through the wing, butted to the front of the support tube. This eliminates the tendency of the servo to wiggle side-to-side rather than move ailerons. It's a hair trickier, but no big deal.

I also like to put the servo arm above the wing. Not only does this keep grass out of the linkage in typical emergency yard landings, it generally sets the aileron differential to the top side (less drag).

First make the cut and put the servo in. Here's how it looks installed:

timocharis 11-24-2005 02:36 PM

Aileron Servo Cutouts
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Next we get to make servo cutouts in the fuse. It's a lot easier to do now, and of course you must make room for the aileron servo before sticking things together.

Now that you have the servo in the wing, the easy trick is to slip the wing in from one side and trace the cutouts. Put down some masking tape first, and draw on that. On the top, make sure to leave plenty of room for the control arms to swing front-to-back.

timocharis 11-24-2005 02:36 PM

The Servo Bottom Problem
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Generally, you'll want the wire coming from the servo to face the rear (due to receiver placement). So you'll want to leave some room. Also, this is a great place to route your battery wire when the time comes (the battery must be on the side opposite the rest of the electronics, such as the ESC. As a result, it has to go through the fuse).

But how big to make the gap? It depends on whether you're reusing an ESC or just got a new one. If new, you can leave a fairly small gap -- just big enough for all the wires. You can then solder on your battery connector after you put the wires through the fuse. Slightly tricky, but neater.

On the other hand, if your ESC already has a battery connector and you don't want to desolder it, leave enough room to slip the connector through.

I was resoldering anyway, so here's how my gap trace looked:

timocharis 11-24-2005 02:37 PM

Tail Feather Servos
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Your last servo cutouts. There's only one solid rule: keep the servos, arms and rods below the wingline. This almost seems counterintuitive, since you'll probably be landing right-side-up most of the time, so why wouldn't you want to keep this stuff away from the ground?

Because sooner or later you'll want to both launch and catch the plane by the scruff of its neck, and if there are wiggly electronics there, it takes a lot of the fun out of it. Also, they're pretty close to the fuse and unlikely to get into any scruff.

It's possible to run both control rods on the same side, and there are good arguments for it. I use opposite sides, and obviously think there are good arguments for that, too.

Front-and-back or top-and-bottom are fine. The layout is not particularly important. I tend to favor front-and-back with the rudder servo sternward. I used top/bottom this time for various reasons having to do with the Cirrus servos being useless and having a wrong-sized servo cutout.

If you face them on opposite sides, one of the wires will have to come back to the receiver side (normally the left). I just cut a slit and slide the connector through. You can reglue it afterward if you wish. Use masking tape, trace your cutouts, and make the cuts. If you're worried about it, make sure all three servo wires can make it to the receiver position (which will be roughly halfway between the two servo groups).

Here's how the layout ended up:

timocharis 11-24-2005 02:38 PM

Front Support Tube
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Just for fun, I added a bit of .125 carbon tube to the front of the wing, going into the fuse kerf where the wire went through to make the wing slot. This is not at all important, I'm sure, but it does fit nicely and seems like a natural exploit.

If you like the idea, just drill a hole in the front of the wing and slip the tube in. Make sure it goes nowhere near the servo or near the motor mount position. You want those areas to be flexible in a crash, and you don't want a carbon tube impaled in your aileron servo.

timocharis 11-24-2005 02:39 PM

Tape On The Ailerons
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I find it easier to mount the ailerons with the wing lying flat, and this is just about the last chance we'll have. Of course, you could do this earlier, but it would mean having ailerons flop around while you fuss with everything else. Trust me, this is the best time (even though you have to cope with the servo).

To make sure you get enough throw, tape the bevel side first with the aileron lying on top of the wing, effectively at 180 degrees of throw. Then turn it over, bend the aileron to at least 45 degrees, and put on your top tape. There should be a small gap left between the aileron and wing. Run a toothpick or piece of balsa along there to make sure tape sticks to tape in the gap. This adds strength and support while making a precise and easy hinge.

I used 3/4" EPP tape, which requires no preparation. You just stick it on and you're done.

Finding a tape that sticks to EPP is something of a minor miracle. This is the first plane I've tried it on, and it works quite well. I don't know how it will stand the test of time, but I see no reason to expect failure.

I do slightly prefer blenderm because it's a bit more flexible (so easier on the servos) but it requires a substrate for adhesion. This means, basically, masking off the surfaces to be taped and slathering on Elmer's or Canopy Glue and letting it dry. Tiresome, to say the least. If you're lazy, get some of the EPP tape. The only convenient source I know is slofly.com, and the price is perfectly reasonable. You'll have to leave a slightly larger gap (test some!) to make sure you can get full throws, since the EPP tape is a bit thicker, like typical strapping tape (which it is not!)

It's a bit visible, but not offensive:

timocharis 11-24-2005 02:40 PM

Install the Stab/Elevator
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All this fussing is fairly easy to do in one evening, and now it's time for the scary big assembly.

Do the stab first. It's easier, and won't flop around much while you're doing the wing. I sincerely suggest using white glue for this process: adjustment time is a real boon.

First you'll want to practice inserting the stab: pry the tail open like jaws, and jam the stab in. Make sure the elevator has enough cutout to move 50-60 degrees up and down. If the cutout is too small, enlarge it with your knife. When this is all hunky-dory, glue it in.

It's easiest to put a glob o glue at the front of the cutout in the fuse, then some glue on the top and bottom of the stab. Since you used white glue, you don't have to be precise in the stab placement at this time -- just get it roughly right and move along to the wing.

Here's mine with full up. Note there is extra room in the cutout -- that's a good thing!

timocharis 11-24-2005 02:41 PM

Install the Wing
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This is a bit trickier, but no big deal. Practice at least once. I like to put all the glue in the cutout, avoiding the areas where nothing will be stuck (like the servo arm area, or where the wires go through the fuse).

If you used the goofy carbon tube at the front of the wing, don't concern yourself with it at this time.

This step goes best if you can get some help. Ask a neighbor, friend, wife, kid or dog to hold the "jaws" open wide for you, and sneak the wing in. Make sure it's straight against the bottom of the cutout. Then take the fuse back and lower the top into position.

Put it on the blocks (or books, or whatever) you've already prepared for this stage. Do your final fussy alignment, then walk away and don't touch until tomorrow. No matter what kind of glue you decide to use, follow this advice. This is an overnight step. You want the grip firm and the alignment as good as you can get before you start the finishing phase.

timocharis 11-24-2005 02:41 PM

Motor Mount
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There are a lot of ways to mount a motor to one of these planes. Hundreds. But my favorite is the Slofly motor mount (if you're using a CDROM motor, a Komodo, a Little Screamer or any other compatible motor shaft).

It's cheap, easy and allows quick motor exchange.

You just put some thick CA top and bottom and slip it into place. Adjust until it's all straight, then let it sit for a while. That's about all there is to it. Later, you'll support it some more.

timocharis 11-24-2005 02:42 PM

Control Horns
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This is another "million ways to do" situation. I've used the DuBro mini horns, made my own from plywood, used Horsefly Hobbies ply horns, etc. All are fine. My current favorite is using old GWS horns. Just cut off the ratchet tabs, shape the front a little, and jam them all the way through the EPP.

This makes for a very solid bond, and they end up just about the ideal length. Also, they're nearly invisible.

I suggest gluing with thick CA. Most other glues don't seem to stick to the weird GWS plastic very well, though epoxy also works fine. I'm sure gorilla glue would hold and look awful too!

timocharis 11-24-2005 02:43 PM

The Nose
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The last thing before installing electronics is building up the nose. I like to put a bit of EPP (remember that scrap?) on each side of the motor mount, running back to the wing.

Shape is not particularly important. I do bevel the front and back for air flow reasons. I also like to have enough surface to stick on some velcro for the battery; if I want to front-load the weight, putting it in the middle makes for better balance.

Just before you put the nose covers on, put some CA on the tube sticking out from the front of the wing, and some extra glue of whatever sort against the sides of the motor mount. Let it all dry down good and solid, and nose-ins will usually not require any repair at all.

Just don't make it too stiff. Better to break some foam than a motor.

timocharis 11-24-2005 02:43 PM

Electronics Layout
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The point is to put as much of the electronics on the side opposite your battery mount. This gives you the best chance for a good balance.

You already know where the servos go. The placement of the receiver is implicit. I prefer to use the right-angle GWS variant, but a straight-out plug set can also work.

I like to put the ESC right behind the nose support, a good distance from the receiver (to avoid signal noise). I prefer to run the antenna back along the body rather than the wing, but I consider this a finicky point, not important. Keeps away from the ESC.

For reasons that border on superstition, I like to cover the receiver and ESC with 3M Transpore tape, then glue them in place with thick CA. Any tape is probably fine, but you should consider keeping the top of the ESC open to the air for cooling. In practice, mine don't get warm so maybe it's not that important.

The aileron control rods are just standard wire, since they're so short. The tail feathers are connected by .060 (1.5mm) carbon rod. Using that heft, you won't need any guides or supports. Attach wire to each end using thread, CA and heat shrink to cover the mess. One end gets z-bends, the other inserts into DuBro Mini EZ-Connects. Or whatever system you prefer.

Here's a picture of the setup. If you want to run your antenna along the wing, turning the receiver around works best. You can't really see the battery line running through just behind the aileron servo.

timocharis 11-24-2005 02:44 PM

Final Notes
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I like to use the new E-Flite extended servo arms on the aileron and elevator servo. Lots of throw, and weirdly they work on both the HE servos and the GWS Picos. I have no idea why. The rudder generally won't have as much play, and can get by with a more modest arm, although you may have to extend a typical GWS arm if you go that route.

Your batteries must match your motor. I've been quite pleased with the LensRC 20-turn 22.7 (I think slofly.com is the only place you can currently get one. Of course, you can order a $12 motor kit and build your own, if you're up to a 20-turn wind. Or just custom order one from lensrc.com for the same price).

For this motor, I'm primarily using the Thunder Power 730 2s with a GWS 9x5 prop, or for a real scream the Kokam 340 3s with GWS 8040 prop. The latter will curl your hair!

The list of motor possibilities is endless; I'll leave that for further speculation.

No doubt I've forgotten some things. With any luck, I can edit them in, and I'm sure others will contribute to pick up the slack.

Dave North
November, 2005

timocharis 11-25-2005 08:18 PM

Okay, some flight notes.

I find the plane relatively easy to fly in a 9x12 bedroom. It's very stable. In my 16x16 tree-lined back yard I can stay up as long as I like, do flips, rolls and high-alpha knife.

In a larger field, the outstanding characteristic is smooth, minimally coupled knife. With only a little orientation familiarity, you can just wander around the field more or less at will.

In other words, it's within a breath of shockflyer performance without being at all delicate. If that doesn't interest you...


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