da Rock

Years ago, MANY years ago, I was repeatedly beaten by The Soaring God of the North in the contests the MRCSS were silly enough to run. He would come south from Duluth with his Bird of Time and kick our butts. I think he even came down on a motor cycle one time. Don't ask. He's a Soaring God and they do fables like we do lunch.

Anyway, I swore I'd build a Bird some day. Maybe it'd make me a god.

Turns out I did buy an ARF Bird a few years back. Not a good move, as ARFs turn me off right after turning me on. I get excited as Zeus and buy them, then open the box and decide to assemble the parts some day when it's raining.

Now I've discovered the extreme difficulty of my new home. No places to lay out a hi-start or winch. None. So I've been fiddling around with a Spectra. Spent about a year working out it's power system. Nothing that was suggested was available. Well actually, half of each system that was suggested was available. Quite a few systems were suggested, but every one had a critical member out of stock. None of them combined their available parts with other systems available parts ............. blah blah blah...... whine whine whine...............

anyway.........

Has anyone got a good system in their BOT that actually has all the parts in stock somewhere?

Yeah, I know I'm asking a lot, but I am ROYALLY tired of trying to outfit electrics. The Spectra was just the first. My last conquest was a kewl looking little Eagle that required smaller motor than anyone sells. A few are advertised just like ones for sale, but aren't in stock. I could buy 3 so far from China, none of which worked, of if did work, kept working. So it's either ask for everything or not do the Bot.

sorry to be such a bother. If it really is a bother, don't bother, I understand and won't be bothered by that.

But if you'd like to be somewhat responsible for the creation of a Soaring God (unfortunately a lazy, good for nothing one) then tia.

AmishWarlord

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Hey Rock I have planes for a BOT. I have a huge bash in mind but lately I think I just may build a simi-stock in electric to see how it goes.
There is a guy on RCU that has a real nice set up

http://www.rcuniverse.com/forum/m_10...m.htm#10397114

AmishWarlord

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http://www.rcuniverse.com/forum/m_10...m.htm#10397114

Good old post with lots of links.

AmishWarlord

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http://vimeo.com/21112617

Eletric BOT video

da Rock

Thanks for the link. It's refresing to see one that points back into RCU.

Only problem with that thread is "the guy" really only describes a setup that was tailored from what sounds like the prop he had available. "He" even suggests readers would be advised to come up with something better.

I am of course intrigued with his promise to build a V-tailed Bird of Time that'll use a pusher motor. Wonder if the motor is going behind the V or between it. Putting the motor between the stabs would of course protect the prop on landings.

AmishWarlord

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"He"

LOL I know what you mean. I don't think the first photo is the real Kiwi Kid, I'm thinking that fellow behind the BOT is the real Kiwi Kid.

AmishWarlord

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I'm thinking a .15 or .20 size electric set up would do.

Guy named Cliff at my club used a .15 in his and it took it up pretty well. I think if we used a .20 sized electric system it would carry the extra battery weight and perform like the .15 nitro engine did.

AmishWarlord

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Here is a .20 size power system (motor-mount-prop-esc-lipo) and the wing spoilers and servos for the BOT.

Comes out to almost a pound.

The stock BOT is listed as 3.75 pounds.

So with the extra wide fuselage, power reinforcements, folding prop and spinner, and the rest of this junk in it, I think a weight of 5 pounds would come out.

This would give a wing loading of about 11oz. foot²

skeeter_ca

Why is that girl in a red, white and blue bikini holding a russian jet? And yes, look again there is a jet in the picture!

skeeter

skeeter_ca

DaRock i feel your pain.

I have a BoT kit in a box just itching to be built. I haven't seen any complete power systems that would work good with it. Folding prop would be a must on this system of course. I would like to see something that is availiable that can be order within the US.

skeeter

da Rock

Guess the thing to do is go simple.

What's the rule of thumb? 100W per pound system for a trainer. 200W/lb for aerobatics. 300W/lb for 3D? or something like that. OK, that's 3 rules and only one finger.

So anything that's somewhere from 750W to around 1000W should work. That is if I've got the "3 finger rule" right.

AmishWarlord

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I like 100w for motor gliders. So 5 pounds X 100w = 500w

500w ÷ 3g per w = 166g motor

166g motor = about a 42-45 motor

RimFire .32 850kv = 42-50 at 198g

198g x 3 = 594w

80% of 850kv = 680kv

680kv X 3S-11.1v = 7548 RPM

13.5" X 7 prop at 7548 RPM
5.06 Pounds static thurst
50 MPH prop speed
499w
44.9 amp draw

60 amp ESC
Battery 3S 4500 Lipo

Hydro Junkie

AmishWarlord, do you mind putting that in english? I need to figure out what motor and power source to put into a Goldberg Electra and I didn't really understand much of that[X(]

AmishWarlord

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PM sent.

Wheww that was a lot of typeing!

skylark-flier

Yup, it's a jet alright - MiG-29 (NATOcodename - Fulcrum). The girl could quite possibly be Russian too, she certainly looks the part. Remember, their new colors - since the de-revolution - is (in order) white, blue, red. (pic below)

Dave

AmishWarlord

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And the cammo pattern on those pants. LOL

AmishWarlord

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I was looking for Russian camo and as usual I got distracted.

Anyone know about that cool looking UAV in the back ground?

Man this thing is way to slick in design to be Russian.

skylark-flier

I may be quite wrong but this UAV of yours appears to be the "new" MALE (yeah, that's its name) UAV being developed by Dassault Aviation, working with the Israeli company IAI. Basically, it's a modified version of the Heron TP airframe. It's still in the development stages as far as I know. This could easily be the prototype.

AmishWarlord

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I've seen that one and it is as blocky as an ungly stick.

That Russain one is slick and has rounded booms.

scaflock

Hey Rock...

I used a E-Flite Power 20 on my Paragon which has about the same size and weight at a BOT and found it to be a tad light on the power.  Keep in mind that you don't HAVE to use all the power available from your motor setup.  Tiz a far better thing to have the power and not need it than to need it and not have it to call on.  BOT uses a different airfoil than the Paragon and it's not quite as much of a floater.

My advice would be to build the BOT at light as possible, strong as you can make it and as straight as you can.  It's a great classic design that can only be made better with a good electric setup.

BMatthews

Well, I may as well jump in as well since I've got a BOT that a good buddy built and eventually sold to me.

Mine is a touch overweight at around the 55 oz range. But since it was built with one of the then new Selig airfoils it handles it well. But still, I would not suggest building it any heavier. I'd also suggest looking at using one of the newer airfoils to replace Dave's original "TLAR" airfoil. A Drela AG34 with the same makeup for sheeting and spars as his Allegro Lite would be my suggestion.

Either way if we're looking at around 50 or less oz for weight and you're OK with around a 45 degree climb at a decent "non stall'y" sort of speed then 70 watts per lb will do the job. Or for a bit more oomph go with the fairly accepted 100 watts/lb. Assuming you can hold the overall weight budget to 50 oz or less we're talking about only 300 watts. And these days you can get that much motor and pack for a song and a dance..... or very little pain on your charge account in case they don't appreciate the Arts...

To ensure you're not pushing the motor I'd go for a 350 to 380 watt max continuous capacity just so that the motor isn't on the edge all the time.

The more "commercial" option to me suggest that you'd be fine with an E-Flite Power 15 motor. It's rated at a max 34 amps over 7.4 to 14.4 volts so even at 28'ish amps from a 3S pack you'd be well under the max continuous power if proped right. Yet you'd have a 55 to 60 degree climb at a good clip of speed. The prop range called for suggests that something around a 12x6 to 13x5 would do the trick.

On a budget? Then these picks from Hobby King look suitable;

http://www.hobbyking.com/hobbyking/s...ner_810kv.html
This one is just over 5 oz. And that's a good thing since BoT's seem to need some extra nose weight. At a max current of 42 amps it'll be loafing. It'll need around a 13x6 or 13x7 or even a 14x6 prop to lug up the current on 3S packs. But if you can go with a 4S then it'll reduce the prop a bit.

http://www.hobbyking.com/hobbyking/s...ner_Motor.html
At slightly lighter but with a higher Kv value this looks like a winner. Props will drop to 12x6 to 13x6 inch range to get power levels in the 300'ish watt range.

The only thing missing here is the actual prop to use with the motor. Unfortunetly it's hard to tell you which prop will do the job. To know that you'll need to wait for someone with a 300 watt setup to drop in and tell you what motor they are using and with what prop and what sort of pack (2S, 3S, etc). Because so many motors come with various Kv values there's just no way to say that such and such a prop will draw X watts when it's got some stated Kv value. Add to that the simple fact that the budget motors from such places as Hobby King seem to be a bit "variable" on the actual motor to motor Kv value and you end up needing to get a watt meter and do some testing. Or at least know someone with a watt meter that you can borrow.

As for the ESC that's easy. You'll want one which can handle a minimum of 40 amps. 45'ish would be ideal. And even then you'll want to mount the ESC somewhere it gets at least a whiff of airflow past it. The more the better. Similarly with a 300 watt setup you'll want the motor to get the benefit of some air being directed so that it forces its way through the outrunner bell to aid in cooling the windings on the stator.

One fact is a slam dunk. Any time anyone puts a BoT into the air the sky is a prettier place to ponder. All the best with the project.

Hydro Junkie

I can believe it, took a while to read as well. Many thinks and now go put your fingers on ice for a bit

skeeter_ca

Well DaRock,

It looks like you didn't really get the answer i hoping for huh! You received plenty of recommendations on the motor sizes with a few prop sizes. But as i recall you were wanting to know what package deal i.e. Motor/prop combo would be good for the BoT. Most importantly what motor and folding prop that is available at present time to make a power package. All you seem to get, which was helpful is how to figure out the motor to use.

So maybe we can phrase it a little better this time. What motor and folding prop are you folks using on your BoT or similiar span/weight glider. If you can please be specific with brands, sizes and part numbers if possible. If that info is available we can then see if the parts are still available to order.

I too am going to start my BoT as soon as i finish my SS60 build so this info would be very helpful. Maybe i'm jumping to conclusions DaRock, did you decide on a power package yet?

skeeter

da Rock

Decide on a power package? Nah..... really was looking for someone to say what they'd found works.

I'm somewhat disenchanted with electric right now. Truth is, if someone did list their favorite combinations I'd bet the farm at least one part would be out of stock but due to be restocked 6 months ago.

skeeter_ca

This electric stuff really burns my but. It take two many wrong pieces to finally get a good working combo. I would love to see a good motor/folding prop combo that is available from one source, preferably in the US, that is not so high priced i have to take out a loan.

skeeter