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Please advise on 8 motor power system...

Old 10-24-2013, 02:48 PM
  #26  
cyclops2
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My China Clipper had a HUGE COG problem.

All the weight is in that long tail section . None in the short nose. I had to go to massive NIMH battery to get it to glide.
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Old 10-24-2013, 04:08 PM
  #27  
HugoW
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Originally Posted by CHELLIE View Post
Hi, I read some of the comments on that motor, and some were saying the bearing get rough after a few flights, i would steer clear of that motor IMHO.
True, I might look for a similar motor, of just throw in some new (non-China) bearings.

Originally Posted by CHELLIE View Post
Before I forget figure out what the wing loading will be at 3000 grams, 6.6 lbs, you may need to make the wing longer or wider if the wing loading is to heavy....
One of your links lets me calculate 26 oz/sq.ft. That indeed is a bit much, I might set my weight target to 2500 grams. With the drawings getting more finalised and the motors turning out lighter than expected, that should be possible. Down to 21 oz/sq.ft.

Thanks, I love the gasser goose. That would be a nightmare… I have dreamt of building one with eight Brown Bear radials:



Span would be 9 yards, budget 100k. Dreaming… Although it could turn into a nightmare, easily.

@fhhuber; thanks for the advice, most I have already taken into account. I will have experience with other multiengine planes and seaplanes before this project will ever be ready to fly. My Catalina, Ivan P. design, is under construction…

@cyclops2; yeah, CG is another issue, packs in the nose would be the best. I will do the math on wire gauge, length and weight. It might be worth running long wires between ESC and motor, to get the packs in the nose and CG correct.

Cheers,

Hugo
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Old 10-24-2013, 11:43 PM
  #28  
cyclops2
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That saves you from the DREADED LONG BATTERY LEADS PROBLEMS with some touchy ESCs. I have bench tested 30 amp BP Hobbies ESCs with 4' long battery leads & never blown up a capaciator on a ESC.. Luck ? Could be.

Long motor leads.

I used a flat bottomed airfoil for the wing & tail. Lets me hand toss & glide easily
Almost forgot. I changed the rudder & elevator push rods & sleeves to 10# braided fishline as a PULL - PULL setup. FAR FAR lighter weight in the tail section. No slopiness at all.
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Old 10-24-2013, 11:59 PM
  #29  
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Lots of tricks for saving weight in the back end, and with planes such as the China Clipper or Spruce Goose you need to use them all.
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Old 10-25-2013, 12:03 AM
  #30  
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Right.
I just recently hollowed out the body from the COG point to the vertical stabilizer. Had to move the battery around. It has 4 brushed 400 motors.


Edit I use 1 large ESC & only 2 feed wires. Cheap & very simple I may use some of my old B & D A123 2300 cells. Better than Lead.
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Old 10-25-2013, 12:44 AM
  #31  
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Multis do make you tempted to go back to brushed... One big ESC can run all 8 motors with brushed. 99% reduction in chance of imbalanced thrust.
This might save quite a bit of money also since the brushed ESCs can be found used cheap.

There is not as huge a difference between brushed vs brushless as the difference between NiXX vs Lipo.
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Old 10-25-2013, 01:24 AM
  #32  
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Hobby King is still selling all the Brushed Motor stuff cheap.

RC car stuff is brushed also.

Thought by now there would be no brush stuff around anymore

I forget. All fishing boat trolling motors are still brushed motors. 40 # thrust is in the 8' WW II PTB I built.
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Old 10-25-2013, 04:18 AM
  #33  
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could easily source 8 old gws motors and split the esc's by length/amp rating.
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Old 11-05-2013, 11:30 PM
  #34  
dangaras
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Originally Posted by HugoW View Post
Well, yes, I just cannot help myself...

I have started engineering on a 6 foot semi scale Hughes H-4. And I want to run all 8 motors, no fakies. I have decided to go brushless, and equip each motor nacelle (right word?) with an ESC and a LiPo. Just run signal wires through the wings. Or I will mount a big battery in the nose, and all ESCs there too, running 24 wires through the wings to the motors. I still have to calculate with balance and weight. Using the Ivan P building method, I'm aiming at 3000 grams AUW.

OK, so power-wise, I would like to be at 700 Watt, since it's a float plane. Hey, let's go nuts, take 800, divided over 8 motors, makes 100W each. I'm good at math, aren't I? Now I want to run a 4" 4 blade prop, because that would be most scale, but this is not a must. 3S has my preference, although 2S would be an option. At 3S, 100W is 9A, at 2S 13,5A. No big numbers there.

Here are my first guesses at what to buy:
http://www.hobbyking.com/hobbyking/s...dProduct=31690
http://www.hobbyking.com/hobbyking/s...dProduct=32551
http://www.hobbyking.com/hobbyking/s...cro_Motor.html

Please feel free to com

Hugo
Hugo,

I built a T&J B-29 that weighs about 7 lbs. I used 4 * 2830-1000kv motors, 1 * 3cell, 3600, 40C and she flies like a dream. Takes of from grass fields easily. I am using MA 8*6 3 blade props and some FMS B-25 props.

I also have an X-1 (scale) that weighs over 1 lb that is dropped from the B-29. The 29 lifts & flies with the X-1 attached like it isn't there..

If you were to use some MA 5 inch 3 blade props with 1400kv 2830 motors you would be in fine shape.

All the crap people post about battery leads being too long is a CROCK! Cooked up by ESC manufacturers to sell cap packs & crybabies who buy ESCs that are too close to the current they have to handle. None of that nonsense with my twins and multis over all these years and no failure yet.
.....
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Old 11-06-2013, 01:18 AM
  #35  
dangaras
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Default B-29 & X-1 build

Link to build thread, http://www.rcgroups.com/forums/showthread.php?t=1721130
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Old 02-03-2014, 11:27 AM
  #36  
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Well, it has been a while, but the plans have changed seriously. I have scaled up to 110" span, and I have some test motors running (brushless) with Ramoser Varioprop 4-blades on, 6" diameter. Scale, and good performance. It might just all work, somewhere in the coming decade... I have reversed math on this; the Varioprop can handle 17k rpm max. Divide by 3S = 1532kv. So, still looking for 100+W performance I bought this one:
http://www.hobbyking.com/hobbyking/s...arehouse_.html

Now I need to clean up the workshop and get the things tested. I think this would work!

Hugo
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Old 02-03-2014, 12:08 PM
  #37  
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AWSome!
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Old 02-03-2014, 12:29 PM
  #38  
CHELLIE
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Originally Posted by HugoW View Post
Well, it has been a while, but the plans have changed seriously. I have scaled up to 110" span, and I have some test motors running (brushless) with Ramoser Varioprop 4-blades on, 6" diameter. Scale, and good performance. It might just all work, somewhere in the coming decade... I have reversed math on this; the Varioprop can handle 17k rpm max. Divide by 3S = 1532kv. So, still looking for 100+W performance I bought this one:
http://www.hobbyking.com/hobbyking/s...arehouse_.html

Now I need to clean up the workshop and get the things tested. I think this would work!

Hugo
Happy New Year Hugo Where have you been Hiding at I Think you Got it Now at 110" vers 72" with 6" props, Just build your plane a lite as possible, I would Balsa stick build the tail section and fuselage and not sheet it, just cover it with Monokote or equivalent covering, the bottom 1/4 of the fuselage i would build from foam to make it water proof, Soak the ESC in corrosion X in a jar for about 3 days to water proof them,
Just my 2 cents worth Take care and have fun, Chellie

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Last edited by CHELLIE; 02-03-2014 at 12:44 PM.
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Old 02-03-2014, 02:09 PM
  #39  
HugoW
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Hi Chellie,

happy 2013 to you, too! (or did I miss something?!?)

I've been working and catering after the kids (2 and 4,5 now), and rebuilding the house. And developing a new pylon racer for this season, as I cannot show up with last year's plane, of course...

Your idea about the foam belly sounds good, the plan is a full stick built fuse à la Ivan Pettigrew's Martin Mars, I look at this for inspiration:


That plane is only four engined, but it is the same span and they make it fly at 120" span, at around 4,5kg. I could make the foam (I have a CNC hot wire cutter for the pylon racer wings), but I think the fuse as shown is even lighter.

Cheers,

Hugo
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Old 02-03-2014, 07:19 PM
  #40  
CHELLIE
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Originally Posted by HugoW View Post
Hi Chellie,

happy 2013 to you, too! (or did I miss something?!?)

I've been working and catering after the kids (2 and 4,5 now), and rebuilding the house. And developing a new pylon racer for this season, as I cannot show up with last year's plane, of course...

Your idea about the foam belly sounds good, the plan is a full stick built fuse à la Ivan Pettigrew's Martin Mars, I look at this for inspiration:


That plane is only four engined, but it is the same span and they make it fly at 120" span, at around 4,5kg. I could make the foam (I have a CNC hot wire cutter for the pylon racer wings), but I think the fuse as shown is even lighter.

Cheers,

Hugo
Hi yes the fuse may be lighter in the pic. but it could take on water, where as the foam will displace any water in the hull, and drain out with small drain holes above the foam and water line,
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Old 09-09-2014, 02:06 AM
  #41  
MononkBen
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Default Holy grail of motor/PROP/ESC/AMP/WATT/TRUST/

I am new to RC, and have been researching information for the motors of my own Spruce Goose foamie project...

The challenge is indeed the selection of the right motor and propeller, and the goal is to choose the best compromise of weight, prop, consumption, and trust, in order to get a reasonable weight/trust ratio, as close as possible to 1:1.

I have read carefully this tread and have found a lot of highly valuable information, but I kept searching for something that would help me choose the right motor before I order them. And I think I have found it. It is an excel sheet, with more than 13000 characterization of motor make and models, props, consumption, and trust. I added 2 columns to it: Watts / Weight, and Trust / Watts. I am looking for the smallest prop (my spruce goose is smaller than any spruce goose - 60 inches wing span), and by using filters in the excel sheet, I was able to identify the right motor, prop, and have an estimate of the trust, and compare efficiency (trust/weight and trust/watt).

This information is gold!!! Because the weight increases the trust requirement, and the power consumption increases the battery requirement, which add weight... So for a small 8 motors RC, you need to carefully select the most performant motor in regards to weight, power consumption, and resulting trust.

I think this document contains most of DR Kiwi's tables of all makes and models that you can find at links like this one: [removed link]
(I checked only a few motors and the data is the same).
Working with all the data in a single xls document allows you to compare and select in a glance (using filters).

The excel document can be downloaded from: [removed link]
(google search for it and download directly)

For me, this is the holy grail I was looking for. Hope this can also be useful information for someone else.

MononkBen

I will add the links in another post since this is my first post.
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Old 09-09-2014, 02:09 AM
  #42  
MononkBen
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Default motor/prop/amp/trust/efficiency

Links from previous post:
http://www.flybrushless.com/motor/view/452
http://www.rctoys.com/pdf/prop_data.xls
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