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Old Oct 29, 2012, 08:59 AM
Mark
mlp666's Avatar
United Kingdom, England, Moreton-in-Marsh
Joined Oct 2012
435 Posts
Good to hear your mods have improved the atoms disinterest in climbing.

Electrics are new to me as well, but as I understand it yes increasing the wattage/ampage to near the motor max improves it's efficiency. The bit that confuses me is why they use Amps as a limit! As this will change with voltage i.e. there are 7w to the amp at 7v and 12w to the amp at 12v. There seems to be no voltage attached to a motors ampage.

As for the motor mount I think I'll go for Harry's bulkhead mount approach http://www.rcgroups.com/forums/showp...&postcount=119 as it genially put's the prop near stock. I'll make the bulkhead a little taller so I can adjust the motor height. I haven't done any research yet on the effects of angle and distance on thrust from behind and above the cg.
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Old Oct 29, 2012, 10:27 AM
Mark
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United Kingdom, England, Moreton-in-Marsh
Joined Oct 2012
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After a little thought one option to create a bigger prop clearance would be to raise the wings off the fuselage. maybe a shaped piece of 10mm foam! Wish I hadn't attached the aileron servers to the pylon now!!!
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Old Oct 29, 2012, 11:02 AM
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taz101's Avatar
Australia, QLD, Oxenford
Joined Oct 2010
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The problem with adjusting the height of the motor pod or even the hole wing is you are adjusting the thrust line relevance to your CoG. That is why joker had the instability he talked about in his flite report. There was a big discussion in the Skysurfer/Bixler thread awhile back (just had a search but couldnt find it,over 1000 pages is a lot to go through) but I remember someone say that the thrust line of that plane actually goes through the CoG. Now I know this isn't the same plane but the principle is!!
Below I have found a picture that you can see the relevance to the thrust line and the CoG and how it changes. You can see buy the way Joker has raised the thrust line (but not the angle) how it would affect the flite. One way to fix this I believe would be to adjust the angle of thrust and also angle of the wing (cord).
But buy doing it the bulkhead way you do not adjust anything but slightly moving the CoG back (easier to fix that I think).


LURCH
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Old Oct 29, 2012, 12:40 PM
Mark
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United Kingdom, England, Moreton-in-Marsh
Joined Oct 2012
435 Posts
Hi Taz, Yea I have a Bixler 2 and the thrust line seems to run though the cg. The Atom's thrust line seems to point to somewhere 2 or 3 foot in front of the nose.

My thinking on elevating the wings would be that as the wings contain the CG (he thinks!) raising them would also raise the CG the same level so preserving the existing thrust angle. Though I'm sure someone will tell me why I'm wrong.

M
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Old Oct 29, 2012, 05:46 PM
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Joker 53150's Avatar
United States, WI, Muskego
Joined Sep 2012
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My issue could have been the wind, too. I'm hoping for a calm day soon so I can try it again to be certain. To be honest, I'm not 100% sure I was launching into the wind as the wind direction kept changing. Either way, the launch wasn't horrible - it just wasn't as smooth as the previous day's flights with a stock motor/pod.

Looking at the picture you provided makes me wonder how much of the pod height change will be negated by the larger/heavier 500mAh battery which drags the CoG back down a bit.

As mentioned, after the launch I found the plane very easy to control. It wasn't quite as easy as the stock motor, but that's because I was flying much faster and using high-rates.

Regardless, even if the launch is a little sketchy from this time forward the modifications were well worth the time and effort.
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Old Oct 30, 2012, 04:55 AM
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Australia, QLD, Oxenford
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Quote:
Originally Posted by mlp666 View Post
Hi Taz, Yea I have a Bixler 2 and the thrust line seems to run though the cg. The Atom's thrust line seems to point to somewhere 2 or 3 foot in front of the nose.

My thinking on elevating the wings would be that as the wings contain the CG (he thinks!) raising them would also raise the CG the same level so preserving the existing thrust angle. Though I'm sure someone will tell me why I'm wrong.

M
No the CoG is NOT in the wing!!
The true CoG is in the fuselage somewhere!!
When you balance a high wing plane you do it right side up, but you are only balancing the forward to backward balance point. On low wing planes you balance them upside down, again on balancing the forward to backwards balance point!!
Buy raising the wing you will need to adjust the thrust angle and the angle of the wing cord to have it fly as good as standard.
Hope this helps.

LURCH
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Old Oct 30, 2012, 04:43 PM
Mark
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United Kingdom, England, Moreton-in-Marsh
Joined Oct 2012
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Thanks for putting me straight on that, though it seems that a motors vertical height isn't all that much of an issue given this solution for the bixler http://smallpartscnc.com/index.php?r...product_id=108

M
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Old Oct 30, 2012, 08:22 PM
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United States, WI, Muskego
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Game on! My dad's Christmas Atom just showed up, and as long as my son can keep a secret when he sees Grandpa again it'll be a nice surprise for him.

Some quick quality testing to compare two different Atom's using the same test methods:

Stock Atom #1, 3.6A, 26 watts, 106 grams thrust.
Stock Atom #2, 3.2A, 24 watts, 106 grams thrust.

I find that strange...

Stock weight on the new Atom is 164 grams with all hardware, Orange RX, and stock 250mAh battery. I dont know where HK comes up with 145 grams, unless that doesn't include the battery?

I removed the motor, ESC, and 250mAh battery and replaced them with the Turnigy 1811, HobbyKing 6A ESC, and 500mAh battery. By doing this, the flying weight went DOWN to 158 grams (which includes a few grams to account for tape, Velcro, glue, etc). Once all is said and done I'm guessing the upgraded Atom will come in +/- a few grams from stock.

Not too bad considering it will be heavily upgraded across the board.

With this build I think I'm going to try and keep the stock motor pod setup. It looks like it will be able to swing a 4-1/2" prop without hitting the boom, and I should be able to get enough juice out of the 1811 and a good prop to keep my dad happy until he's ready to graduate to a different plane.

Of the 4-1/2" props I've tried so far the best result was with a 4.5x4 which gave me 2.4A, 19 watts, and 115 grams of thrust. Since the motor is supposedly able to handle 4.1A I've got a little room to play. My next order from HK will include a 4.5x4.5 prop as well as 4.75x4.75. I don't know if the 4-3/4" would fit without more modification, but I'll give it a shot anyway.
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Old Oct 30, 2012, 11:46 PM
looking up down under
scruffy1's Avatar
Australia, NSW, Fairlight
Joined Feb 2008
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my figures for the 1811-2000 (silver version)


4x2.5 drawing 1.92amps producing 13.6watts @12900rpm
4.1x4.1 2.5 16.9 11280
4.5x4.5 2.75 19 9900

hope that helps
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Old Oct 31, 2012, 03:56 AM
Reap the wild wind
headlessagain's Avatar
Bristol,UK
Joined Feb 2007
4,283 Posts
Well, I gave the stock motor with bigger prop a go but only a small improvement on the stock prop. I've now cut away the brushed unit and will fit the 9g pole and stator motor I have. These are the specs
3800kv, 7.4volts, 9 amps,Load speed 14850, on GW/EP 5x3, thrust 225. Of course, these are the dealers specs and we all know how accurate they can be!
I won't have clearance for a 5" prop but reckon a 4.5 x 4.5 should give me similar numbers. Good job I also have a 10 amp esc in stock
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Old Nov 02, 2012, 09:21 PM
looking up down under
scruffy1's Avatar
Australia, NSW, Fairlight
Joined Feb 2008
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a word of caution to the users of c10micro-2900 motors

they are great on 2s, and capable of handling 11v according to their specs, but read the small print where it notes 5amp max

flying the gws5043 on 2s draws probably around 5.5amps, but seems to be perfectly okay from my couple of dozen flights on it

however, when you up the supply to 3s on that prop, you get to see the magic smoke

predictable in hindsight, but i was too keen for my own good to see how the mini-stick flew with that much power and found out the hard way

and for the record : vertically but not for very long
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Old Nov 02, 2012, 11:12 PM
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United States, WI, Muskego
Joined Sep 2012
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That's a big part of the reason I'm testing a few motors with multiple prop sizes/pitches - I want to get close to the max without accidently going over and burning up. I made a spreadsheet showing the motor, max specs, and what I get for Amps and Watts with each prop. Also I've listed the grams of thrust I achieve with each combination so I can better tell what motor to use in a given plane. It's been an interesting way to learn what prop length and pitch really do.
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Old Nov 03, 2012, 01:04 AM
looking up down under
scruffy1's Avatar
Australia, NSW, Fairlight
Joined Feb 2008
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i too have a wealth of info in spreadsheets

my motor sheet includes variations in battery rating / propeller / esc for the various motors, and measures rpm / watts / amps and i have fiddled with an anemometer to record thrust as metres/second as a rough guide, as i lack the scales for better options

the lipos are all dutifully recorded including % use per outing, cross referenced against flight times, exc and prop and airframe


if i could get the enthusiasm to manage a true relational database i suspect it would be even better, but that's another project on the back burner for now

it would be useful if amongst the toolbar options on the message stuff there was a "tables" option, so we could share info without the formatting making it a dog's breakfast
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Old Nov 03, 2012, 09:43 AM
Mark
mlp666's Avatar
United Kingdom, England, Moreton-in-Marsh
Joined Oct 2012
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Quote:
Originally Posted by scruffy1 View Post
it would be useful if amongst the toolbar options on the message stuff there was a "tables" option, so we could share info without the formatting making it a dog's breakfast
I suppose a link to a drive spreadsheet would work, it takes an xls or csv input.

http://www.google.com/drive/start/ap...product=sheets

M
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Old Nov 03, 2012, 02:58 PM
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United States, WI, Muskego
Joined Sep 2012
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Winds were reasonably calm today so the boy and I hit the field to fly the Atom, Super Cub, and a scratch-built foamie. Up first was his Atom. My last report said it was a little shaky on take-off, but evidently that was from the wind. Today it took off very much like it did before the modifications (although with a lot more power). We took turns flying it and warming our hands (low 30's today) and ran a pair of 500mAh batteries through it

Observations with minimal wind: even with the extra weight up high it's still very stable. It'll run straight up for short distances before it runs out of momentum. Turns are still very smooth thanks to the rudder modification. Balance feels right on with the heavier battery in the nose and the ESC and RX mounted under the wing. Landings continue to be super easy and controlled.

The boy did more flying today with it than me, and he did pretty well. I had to take over twice as he was getting too close to the ground once and the other time he was about to fly over a building and I wanted to keep the plane where we could recover it easily. He hasn't tried landing it yet, but that's the next step. Unless you count crashing as a landing, in which case he's a pro.
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