|Jun 18, 2012, 03:31 AM|
Joined Feb 2007
Das Plas-Stick (DPS) - E version full size
I just maidened my first e-spad . I am new to all this lipo brushless motors business so i decided to use what i had from my old gliders from years back. I did buy some lipos as the nicad pack I had went missing along with the charger.... anyway, IT FLIES!!!!! but only just.
Had real trouble balancing it with all the weight of the tail.... so with the wing as far back as possible (the access hatch is showing by 5mm. and all the battery and motor and esc jammed right up the front with no room to spare and a couple of lead fishing sinkers, I couldn't wait any longer for a nicer day (damn winds).
Took off nice and smooth but very slowly and missing the curb by and inch with no elevator after about 13m. Had it on full throttle the whole time to keep up the speed though which was disappointing.
After it sounded like the power was dropping off and going flat (it only flew for 3 mins each battery). Landed it a bit rough and bent a wheel a bit but all good.
SO my question is.... I need a bigger motor - and battery - and esc....
The specs currently are:
Fuse (5mm coro)
Wing (3mm top/5mm bottom) its all i can find where i live.
Tail dragger with now bent front legs.
Motor: a pretty big cylinder brushed motor (which got red hot and started melting my plane after the second flight. Think its a speed 600 or bigger if there is bigger than that. Theres no writing on it. Stinks alot now I thought it would be able to handle a 2 cell battery without cookin. very wrong.
Esc: U-whizz 40A brushed esc
Batt: 2200mah 7.4v 25-35c turnigy
Elevator and aileron only (standard old servos)
I will get some kitchen scales to weigh the plane but its around the two kilo mark AUW off the bathroom scales.
I'm getting all my stuff from hobby king so if someone who has built this Spad before in electric in full scale can they give me the best options for motor, batt, and esc to suit. I cant seem to get my head around this in-out runner business so if someone people can make my decision for me, from experience, I would be very grateful.
The aim of this is to get a couple of combat models for me and my brother to have a bash around chasing streamers. Just want to get a prototype working well first.
Thanks alot for taking the time to read all this.
ill get some photos up in a sec
|Jun 18, 2012, 11:39 PM|
Every electric plane I've built so far I've only used what equipment someone else used with success. There are a lot of threads that'll help you match a motor, esc & prop to a plane. My take so far has been that you need X watts per pound for the type of plane you're flying and for a DPS I'm guessing you'd want 100 - 125 watts per pound of plane. Of you could go nuts and strap something on there that'll tear the control surfaces off. Then you'd want to match the Kv and prop to how you want to fly. If you want to fly slow and floaty, you'd want a lower Kv and a bigger prop. If you want the boogedy, boogedy, boogedy, you'd want a higher Kv and a smaller prop, all in the same range of wattage and ESC capability. I know there have been E-DPS's built and highlighted on Spadworld.net, so you might want to log on there and search for that. I also have a subscription to a "how to" for motor and prop selection that I'll link here in just a sec. Pretty sure Chris or Clean or one of the guys who actually know what they're talking about will be along shortly.
|Jun 26, 2012, 05:16 AM|
Joined Feb 2007
Thanks so much for your help Johns Pop. That webocalc thingo is brilliant (NFZ being suspended is a pain in the bum having to unhide every single one of his great posts, one post at a time!).
I think I have it nutted out. Being on a budget for the next few weeks I made some home job scales with a plank as a seesaw. With the plane on one end and at the other, at the same distance from the center of the plank on a texta, a can of condensed milk, a box of rice flour and some vanilla cake mix balanced quite nicely.... weighs in perfectly at 1069grams dry weight with receiver, servos and esc (no motor, prop or battery).
The motor I am looking at is Turnigy D3548/4 1100KV Brushless Outrunner Motor
I'm after vertical climbs in-case I crash this bad and build a bigger future plane.
Not really sure what ESC to go for so I was thinking a Turnigy dlux 70A SBEC
Only based on I read somewhere its better to have a higer rated Amps ESC than the what the motor (50A) wants. Correct??? Would you suggest something else?
Then this finally brings me to the battery. Just taking stabs in the dark at what i think is ok, but i am going to go with is ZIPPY Flightmax 2650mAh 5S1P 45C
I still have my 10x5 prop which I hope is ok. I cant go any bigger or it will scrape the ground. I can always goto the local shop and get a smaller one if you recommend it.
This brings my AUW to around 1670grams. Am i overpowering it way too much? I don't mind it fast. I want to do FPVs later.
I'll attach the webocalc screen too.
Chris or Clean any recommendations?
|Jun 27, 2012, 04:03 PM|
I've just finished up a new version of WebOCalc (version 1.7.6) and uploaded it to my website. You'll find it in the same place as before, i.e.
http://flbeagle.rchomepage.com[/url] -> software -> WebOCalc
Here's a direct link: http://flbeagle.rchomepage.com/softw.../webocalc.html
WebOCalc 1.7. has a few improvements, including floating tooltips (help) when you hover the mouse over any of the inputs. For example if you hover over "Flight Mission" you'll see a help message explaining the term.
You can also now put in your preference for flight duration (how long you can fly on a charge), and WebOCalc will then try to figure out what size (mAh) battery will give you the flight time you want.
There are also some clean-ups to the GUI and some little bug-fixes.
I created the first version of WebOCalc back in 2004 or so, and posted a few threads on it over the years (usually along with a newly released version update). But as often happens I was too familiar with my own creation to see which bits were tripping up other people trying to use it.
Chuck (NoFlyZone) was the one who could see the trouble spots, and he would give me feedback that helped me improve the program over the years. And then Chuck created that wonderful how-to thread that helped so many people figure out how to use WebOCalc to get their models in the air. He was a very good teacher, and he will be sorely missed here on RCG.
|Jun 28, 2012, 02:46 PM|
Yeah, sorry about that Rezzey. I just posted that link, I didn't realize he had been suspended and that his posts were hidden. Bummer.....
|Jun 28, 2012, 02:52 PM|
BTW, NoFlyZone's blog is still available with a TON of great info in it: http://www.rcgroups.com/forums/member.php?u=106813 Here's an article that discusses watts per pound for an airplane: http://www.rc-airplane-world.com/watts-per-pound.html If your AUW is 1670 grams (3.7 lbs) I'm thinking at 910 watts, you're either going to tear your wings off or you're going to have so much flutter in the control surfaces that the control rods are going to be quickly ripped out of the control horns at WOT.
|Jun 28, 2012, 08:19 PM|
It's not usual to need a huge 5S lipo pack and 500 watts in such a small model - the reason is that it is extremely heavy. 2 kg for a small 1.2 m wingspan is bordering on a flying brick. Is there any way to take some weight out of the model?
Edit: I just realised it's made of Coroplast. Ahh. Now I understand why it's so very heavy for such a small airframe!
Generally speaking, extremely heavy airframes aren't the best choice for electric conversions. Especially with cheap (but heavy) motors, an electric conversion will add even more weight to an already heavy airframe. But prices have fallen to the point where you can get away with it nowadays, so if you prefer to go ahead with an electric powertrain, it's certainly possible.
If you're set on an electric powertrain and nothing can be done to reduce the weight of the airframe, then you would get the biggest improvement by using a larger propeller and correspondingly lower Kv motor than your initial choices.
A bigger propeller makes an enormous difference - you can get much better performance without flogging the batteries and motor any harder. The motor you chose will only drive a tiny little 9" propeller (APC 9x4.5 prop at nearly 1.00 ratio). That's way too small for a very heavy 46" electric model. Ideally something around 12 inches would be a good match to your model, if you can find a motor with a low enough Kv. But if that is not possible, even a 10" or 11" prop would be a big, big improvement over that 9x4.5 prop.
You're also going to need a bigger capacity battery unless you're happy with pretty short flight times. I think 3500 mAh is closer to the mark than 2500 mAh for this model.
Given all that, here are my suggestions:
I like the Turnigy Plush ESC's, and higher capacity ones come with a switching BEC (UBEC). This is good, you NEED a UBEC if you're running on a 5S lipo pack as you propose to do. I agree with you about oversizing, your model might require 45A current, so I'd suggest using an ESC rated at 60A or more. The Turnigy Plush 80A seems like a safe choice:
1) ESC Link (Europe): http://www.hobbyking.com/hobbyking/s...obbyking/store
2) ESC Link 2 (China?): http://www.hobbyking.com/hobbyking/s...ontroller.html
(The ESC you chose may work fine, too. Just make sure it has a switching BEC, or use a separate external UBEC with it.)
You need a motor with a low Kv, and 700 rpm/V is the best I could find at Hobby King. I found two possible candidates, one marginal, one very good.
First the marginal one - this motor is really a little too small to handle the power your model needs, but Hobby King carries very few low Kv motors, so I'll list it here just in case:
3) Motor #1, marginally sized (Turnigy Aerodrive SK3 3548-700kV): http://www.hobbyking.com/hobbyking/s...dProduct=18166
If you use the above motor, be kind with the throttle, and you should be fine. Fly it like a glow plane with the throttle all the way up for extended periods, and the motor may cook itself. (It's gonna be hard to manage throttle during combat flying, no?)
Second, the good motor. This motor is much higher quality and certainly up to the job, but costs a lot more (Scorpion SII-3026-710 ):
4) Motor #2: http://www.hobbyking.com/hobbyking/s...Outrunner.html
With either motor, use an APC 12x8 Thin Electric, and 5S lipo pack. 3000 mAh should get you 6 - 10 minutes, and is probably the smallest capacity worth using. 3300 mAh or 3500 mAh would be better. (20C or higher in every case - these days it's hard to find lipo packs rated below 20 C, so no worries on that score.)
5) Here's one suitable battery: 5S 3700 mAh 25C Zippy.
6) Propeller: APC 12x8 Thin Electric.
I've attached a WebOCalc screenshot of the predicted performance below.
Hope that helps,
|Jun 28, 2012, 08:27 PM|
Coroplast is a very heavy corrugated plastic sheet, but it's cheap and durable, so some creative soul started building (glow) RC planes out of the stuff many years ago.
Jake's plane is built out of this same material, but he wants to go electric.
Incidentally, Jake's model is just one more example showing that "watts per pound" rules of thumb frequently just don't work. Jake's model is unusually heavy for its size, and the "watts per pound" rules fail miserably, suggesting far too little power for this particular plane.
In fact, the watts/lb rules of thumb don't work with small models, they don't work with very light models, they don't work with very slow models, they don't work with very fast models, and they don't work with very heavy models!
Back in 2004, someone showed me those "watts/lb" rules of thumb, and I very quickly found out they were pretty much useless. That's actually what drove me to find a better way - and that better way eventually turned into WebOCalc.
|Jun 28, 2012, 10:40 PM|
|Jun 29, 2012, 04:35 PM|
My apologies if I caused you any offence by telling you something you already know. Coroplast is a pretty niche material for RC modelling and not many electric fliers use it or know about it.
For that matter, the fact that so many people were willing to help out a newbie was the reason I joined this forum back in 2004, when I was a total newbie to RC flight and could use all the help I could get. I'd never even heard of motor kv before then.
I too am trying to help - that's the reason I posted to this thread as well, just trying to help Jake out. Jake's model is an oddball in the world of electric RC planes because of its extremely high weight for its size, and it will take a correspondingly oddball power system to get it in the air properly!
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