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Old Mar 05, 2011, 10:00 PM
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Eagle River, AK
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Build Log
Radical RC Stick 400 3D surface kit

Greetings fellow sport flyers. This will be an abridged build log of the Radical RC Stick 400 with the 3D surface kit option. I was looking for an affordable, lightweight, build-up kit of reasonable size and this kit was my choice. This will be at least my fourth Radical RC kit build and it is indeed a very nice kit. I am one of the first to build it with the 3D size ailerons, elevator, and rudder; therefore, I have included some pictures for comparison showing both sizes of control surfaces.
The first picture shows the kit box, nicely packed and padded balsa, other components, and instructions. The second pic shows the 3D surface kit option.
The third pic shows the power package components. I used an APC 9x4.5 E prop, the Himax 2812-650 motor for Radical RC, a Phoenix 35 esc, a micro ubec (also from Radical RC), HS56 and HS65 servos, and a 5S 450mah battery pack. I probably could have used a Phx 25, but it currently lists 4S max so I wanted to be safe. I'm excited about this higher voltage option and eager to see how it performs in flight.

More to follow shortly. -Todd Woodhouse
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Old Mar 05, 2011, 10:55 PM
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Eagle River, AK
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RRC Stick 400 con.

The next two pics show the framed Stick 400 with the 3D size control surfaces taped on and the regular sized surfaces on the table for comparison. The third pic shows the Stick 400 next to a few other RRC kits for overall size comparison.
-Todd
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Old Mar 05, 2011, 11:01 PM
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Eagle River, AK
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RRC Stick 400 con.

The next two pics show the equipment layout and the fuse with the tail feathers covered and servos and pushrods installed. I chose to use carbon pushrods (not included in kit).
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Old Mar 05, 2011, 11:19 PM
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Eagle River, AK
Joined Dec 2003
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RRC Stick 400 con.

The final three pics (for now) show the top and the bottom of the somewhat finished Stick 400, and one minor modification. The only remaining tasks left are the battery hold down velcro or box and a lot of trim coloring. I'm a slow builder in the winter but I'll post a final pic or two when it is complete. The balance looks like it will come out with the battery just slightly aft of the hatch hole. I'll see after final trim covering is complete.
The weight as you see it is 12 3/4oz plus a 2 3/8oz battery for a total of 15 1/8oz. After final trim, etc it will likely be under 16oz. I decided for now to not install the landing gear and wheels. I'll probably add a lightweight foam fuselage and tail skid for protection.
The final pic shows a minor modification. I did not like the look of the hatch hole which allows the magnetic hatch to be removed. I added a balsa hinged piece with a rubber band hold down from the inside to cover the hole from the inside of the hatch but still allow the hinged piece to be pushed down to remove the hatch.
Here are the initial power statistics: After running for a minute to get past the initially higher battery voltage, I recorded a max amperage of 7.5A at 17.3V for a total of 130W. At half power it was a miserly 2A at 18.5V for 37W. Now here's the cool part. It was hovering at only slightly over 1/2 power! Hovering at 2-3A - you gotta like that.
That's all for now. Keep building light! -Todd
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Old Mar 06, 2011, 06:02 AM
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Very curious ailerons... and power system. Why 5S?
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Old Mar 06, 2011, 06:47 AM
Rho
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What is the wingspam for this model?
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Old Mar 06, 2011, 07:50 AM
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Eagle River, AK
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RRC Stick 400 con.

Wingspan is 34.4"

5S yields high power on low current. Possibly very efficient. To get 130W or so on 3S for 6 or 8 min. of high power flight would take a heavier battery than a 5S 450mah, I think. I'm not an electron expert - anyone else want to weigh in on the high voltage advantages? -Todd
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Old Mar 06, 2011, 08:30 AM
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I may be all wet but your power system defies everything I thought I knew.

I'm not certain but your motor is 650 Kv? That's a good, low value for a motor that size. It's hard to find low Kv values in small motors.

At 2 amps, the best I can get out of WebOCalc is about 8-9 oz. thrust, regardless of voltage. I've always believed that big slow props were more efficient than small fast props. Have I been misled?

I'm amazed and impressed and not quite believing that you can hover a 15 oz. plane at 50 watts. Most hard core 3Ders aim for about 150 watts per pound.
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Old Mar 06, 2011, 05:06 PM
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I'm away from home but I'll test it again in a few days and report back. I thought it was unbelievable myself. Maybe my old wattmeter is not accurate at a 2A and 18V combination. I'll note precisely the throttle position when it's hooked to the meter and duplicate it for the hover. -Todd
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Old Mar 06, 2011, 06:26 PM
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Rafe,

The 5S setup is killer. Of my two Stick 400's I have flying, I fly it the most. It's just too interesting to demonstrate a small high voltage model. Note, his hovering amp test is not the wide open throttle but just the throttle position that yeilded equal thrust to weight. I'm reading inbetween the lines here but i think he was just testing indoors in his hands.

This setup is an example of where I think the hobby is going to be in a couple years. I first tested it a couple years ago. I think higher and higher voltages will be moving into smaller and smaller models. But, at that time I was using a larger battery, now batteries in the right range exist to make this just perfect.

I'm am somewhat suspicious the Pheonix 25 will take 5S, the early ones were spec'd to that voltage, late ones show 4S max. I'm not sure if anything really changed. It may be they just altered the spec range so the 25 wouldn't compete with the 50ICE in any smaller applications. Not sure. Looks like it's working for Todd just fine. Maybe Todd can clarify if it's an early or late control?

In my shop model with this power system, I'm using and HV35 I had. The Pheonix 25 if it's stable here is really the better choice. If we want to use something in current lable spec's, the ICE LITE 50 would be my choice. Listening Castle? I'd love an Ice Lite 10 or 20.

Todd's the first one to complete one with 3D surfaces so we are very anxious to hear the results.

Dave
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Old Mar 06, 2011, 09:45 PM
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Dave, it just sort of flies in the face of everything I thought I knew about e-power.

In a nutshell, what I thought I understood, and what I've been practicing, is to use low Kv motors with big props. To wit: big props spinning slowly are more efficient than smaller props spinning more quickly. (In practice, most of my parkflyers end up with motors around 1000 Kv, except for those like EasyStar that simply can't use large props.)

Unfortunately I can't find a definitive link for that at the moment. But I could drop names of a couple of RCG old timers and smart cookies (eg. the creator of WebOCalc) who hammered that notion into my feeble brain when I first started getting into this hobby a couple years back. The subject is revisited with some regularity, and I've never heard the contrary opinion seriously expressed or defended. You might just be the first.
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Old Mar 07, 2011, 12:35 PM
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Rafe,

My train of thought goes something like this, This model looks like it would fly really well with props in the range of X to Y. I need pitch speed of X, I need watts per pound of X.

I'm open to anything that fills in all the blanks well and decide among them based on how efficient they are, how simple or how interesting. I did the 5S setup originally because it was interesting first and foremost. It also happens to be very efficient.

For example, it's not ideal to fly a 5lb aircraft on a 3S pack. But if a customer comes in and says, I've got 10 of these 3S packs, how can I use them in this model, then the challenge becomes how do we power the model in the right pitch speed, static thrust range with a 3S, 6S or 9S power system. (multiples of the available battery packs) What KV's will get us there and what motor masses will get us the wattage capability? What battery mass is acceptable here and what combinations of available packs are within reasonable weight.

I know that's a little vauge and the thing I have real trouble putting into logical math and rules of thumb are prop diameter choices.

For example, "I don't know how to define scientifically what and explosion is, but I know it when I see it." I have the same kind of fuzzy logic going on when I'm looking at what prop diameters I want to use to work out a model setup.

There are some other things to consider also. If you want to put 400 watts in a model but don't want more than 45mph of pitch speed (lets say it's a slow flying sailplane), you can't do that with any existing 9" props. If you do, you find when you get to 400 watts (to acheive your watts per pound goal) you have way too much pitch speed. You might need a 9x1.5 or something really weird that is unobtainium, so you have to get outside the 9" box and consider larger props. And so goes the if-then-or-else logical way of working through it.

One thing is for certain. I look at what others do as a guide of the norm, but I don't consider the norm to be the right or wrong way to do anything. It's just evidence of a probable reasonable starting point. I don't get transfixed trying to do things within established norms. The edges of my box are out as far as I can imagine with known gear, not deturmined by what everybody else is currently doing.

I know this talk could be much more complete and is a bit rambling. Just dancing around the edges of telling you how I think and resolve a setup.

I don't think other ways of doing it are wrong as long as they acheive the goal the designer has in mind.

Dave
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Old Mar 08, 2011, 07:01 AM
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Rafe,
I think the key to your statements is "big prop and low rpm" which doesn't necessarily mean a low voltage setup, nor a low kv motor. I like to use a general rule of thumb of prop diameter being at least 1/4 the wingspan, and usually no more than 1/3 the span. No science behind that, it just gives you a slightly larger prop than you're accustomed to "in the old days" with glow, which would have generally been a 4.5 to 6 range of prop to span. Sometimes I end up slightly out of that range due to other factors like a particular motor just isn't quite the right KV, and I can't get a lower KV motor in that size nor a gearbox with the right ratio. This setup fits that scenario perfectly, with a 3.8 prop to span ratio. When you get more than 1/3 span with the prop, some flying traits get "strange" due to the torque effects. Higher voltage and lower current are always a good thing, you increase efficiency everywhere, lower excess heat, and can even use smaller wire.

Additionally, watts per pound isn't everything. With an appropriately sized prop you can get gobs of thrust at very low watts. A helicopter is the perfect example of this. It's basically a REALLY BIG prop at low rpms to extract lots of thrust without a lot of wattage. I've hovered a heli at 30 watts per pound for instance. No, not quite practical, rpms too low, but it's possible. I had a smallish sport plane with a geared motor and round cells several years ago(brushed car motor).It was 48 ounces, 3 lbs exactly (44" span) By changing gearing and prop size, using the same motor and batteries, i could hover it with a 200 watt setup, without full throttle. At full throttle that would only have been roughly 66 watts per pound. Hover throttle was probably in the 45 range or thereabouts. This was using a 14 inch prop. The plane flew kinda strange due to the extreme torque changes with throttle changes, and pitch speed was too low to be any real fun. At the other end of the spectrum I had it up to 600 watts (200 watts per pound) with a tiny prop. It would hardly fly (but made a hell of a racket <G>). The "art" is finding the right balance. Dave seems to have done that in this case.

Dave, didn't know about this design. Might have to consider it. Looks like you scaled up the mini stik and I loved mine. My mini stick with the 6X4 and 180 watts on 7 ounces finally left this earth last year You may remember it, the clear covered little beast I flew for several years. It never blew up in flight, but my aging thumbs and reflexes finally gave way.
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Old Mar 08, 2011, 12:33 PM
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What caught my eye was the 5S battery on a 15 oz. plane. I'd just never heard of such an arrangement. I don't own any 5S batteries, and only recently started using 4S -- on a four pound plane (around 500 watts.)

High voltages and/or high Kv would certainly be the way to go on a Funjet, Stryker or even an EasyStar where prop size is limited. Or if you just want to go fast. Where prop size isn't limited, my inclination is almost always in the direction of large prop and low Kv. But then again I like flying light planes, low and slow.

Watts per pound... I've clocked an EasyStar at 25, a Switchback at 17 watts/lb. (Both of those figures measured with 2S power.) These days I aim for about 150 watts/lb. on most of my 3D planes. I imagine a properly geared inrunner (for very low effective Kv) could hover on far less power.
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Old Mar 08, 2011, 12:40 PM
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if you need 100 watts you can get it from 1 amp and 100 volts, or from 100 amps and 1 volt. The former is far better than the latter. Dave is going outside the box in using really small batteries in a high voltage and low current scenario. Same power, but nothing gets hot, everything stays cool and happy, and when you ask for a couple more amps with the "go" stick, the voltage doesn't sag.
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