HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 19, 2012, 05:09 AM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
15,936 Posts
Quote:
Originally Posted by Wormboy View Post
I also use the 14g wire and while it is heavy I have not had any CG issues. In fact I have to push my 1800mah 40C battery as far back as possible to balance correctly.

I will post some info regarding the specs from this system (Amps and watts) as I do recall it pulling more than I expected. I have toasted a couple of 20C 1300mahs when I was first getting the feel of the plane.
Mat
People are often surprised at how far back the battery needs to be. That's why I suggest not gluing the top on the fuselage until the model is pretty much finished and you can do a balance test. Only then do you know where to make the battery hatch. Also, you can't really complete the ESC installation till you know about where the battery will be.

The 2826-6 may draw more current than the standard 2212-6 (by the way, one is named for the size of the casing, the other for the size of the stator, but they are essentially the same size). The 2212-6 takes 23A at WOT on an APC 6x4. That's the static reading, and it drops 2-3A in the air. I wouldn't be surprised to see the other taking 25A static.

My rule of thumb is not to run batteries at more than 50-60% of their rated current if I care about battery life and avoiding excessive heating. Keep in mind that many batteries are over-rated.

So I would consider a 20C 1300 to be good for a steady 13-15A and expect it to be marginal for flying at full throttle. By contrast, your 40C 1800 should easily put out 36-40A.

I'll be interested to see your numbers.
Daedalus66 is online now Find More Posts by Daedalus66
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 19, 2012, 05:16 AM
Registered User
Hong Kong
Joined Nov 2009
58 Posts
Battery and CG

Quote:
Originally Posted by Daedalus66 View Post
People are often surprised at how far back the battery needs to be. That's why I suggest not gluing the top on the fuselage until the model is pretty much finished and you can do a balance test. Only then do you know where to make the battery hatch. Also, you can't really complete the ESC installation till you know about where the battery will be.

The 2826-6 may draw more current than the standard 2212-6 (by the way, one is named for the size of the casing, the other for the size of the stator, but they are essentially the same size). The 2212-6 takes 23A at WOT on an APC 6x4. That's the static reading, and it drops 2-3A in the air. I wouldn't be surprised to see the other taking 25A static.

My rule of thumb is not to run batteries at more than 50-60% of their rated current if I care about battery life and avoiding excessive heating. Keep in mind that many batteries are over-rated.

So I would consider a 20C 1300 to be good for a steady 13-15A and expect it to be marginal for flying at full throttle. By contrast, your 40C 1800 should easily put out 36-40A.

I'll be interested to see your numbers.
You are telling me about battery position. It's barely in the battery tray it's so far back!
ZX10R is offline Find More Posts by ZX10R
Reply With Quote
Old Nov 19, 2012, 07:35 AM
Registered User
Wormboy's Avatar
Australia, WA, Madeley
Joined Jul 2011
623 Posts
Quote:
Originally Posted by Daedalus66 View Post

The 2826-6 may draw more current than the standard 2212-6 (by the way, one is named for the size of the casing, the other for the size of the stator, but they are essentially the same size). The 2212-6 takes 23A at WOT on an APC 6x4. That's the static reading, and it drops 2-3A in the air. I wouldn't be surprised to see the other taking 25A static.

My rule of thumb is not to run batteries at more than 50-60% of their rated current if I care about battery life and avoiding excessive heating. Keep in mind that many batteries are over-rated.

So I would consider a 20C 1300 to be good for a steady 13-15A and expect it to be marginal for flying at full throttle. By contrast, your 40C 1800 should easily put out 36-40A.

I'll be interested to see your numbers.
Static test pulled 22A, 250ish watts so pretty similar to the rctimer. You're spot on with the batteries. I'd never use a 1300 in the Polaris again.
Wormboy is offline Find More Posts by Wormboy
RCG Plus Member
Old Nov 19, 2012, 08:54 AM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
15,936 Posts
Quote:
Originally Posted by ZX10R View Post
You are telling me about battery position. It's barely in the battery tray it's so far back!
I find a typical 20C 2200 3s battery sits about 2/3 on the battery tray.

Maybe the "battery tray" should just be called "front floor" or something to avoid giving people the impression that the battery should fit entirely on it.
Daedalus66 is online now Find More Posts by Daedalus66
Reply With Quote
Old Nov 19, 2012, 02:12 PM
Aussie, Aussie, Aussie!
nrg2go's Avatar
Melbourne, Australia
Joined Apr 2009
1,181 Posts
Quote:
Originally Posted by Wormboy View Post
Static test pulled 22A, 250ish watts so pretty similar to the rctimer. You're spot on with the batteries. I'd never use a 1300 in the Polaris again.
Hey Wormboy,

I'll use nothing but 1300's in all my 100% builds!

Of course I use 1300 45C Nanotechs which gives plenty of headroom current wise and keeps the wt right down. I am getting 8:30 flight times out of my setup and putting anywhere between 70-80% back in to them. Speed bores me to tears so throttle position is rarely near full unless doing some high alpha.

Horses for courses I guess but there are valid reasons for everyone's setup. I would never consider using a 2200 but many do for there own reasons.
nrg2go is online now Find More Posts by nrg2go
Reply With Quote
Old Nov 19, 2012, 02:20 PM
Registered User
Aviefly's Avatar
United Kingdom, Aviemore
Joined Feb 2005
3,244 Posts
Wow 8.5 minutes on a 1300
Aviefly is offline Find More Posts by Aviefly
Reply With Quote
Old Nov 19, 2012, 02:22 PM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
15,936 Posts
Quote:
Originally Posted by Wormboy View Post
Static test pulled 22A, 250ish watts so pretty similar to the rctimer. You're spot on with the batteries. I'd never use a 1300 in the Polaris again.
Yes, that's just about exactly like Suppo/RCTimer. You can figure that will drop to 19-20A in the air at WOT. Polaris will cruise on as little as 9-10A but I generally figure an average of about 15A for normal flying. That gives about 7 minutes of flying on a 2200 or 6 minutes on 1800. But, as they say, YMMV.

EDIT
Looking at nrg2go's numbers:
80% of 1300 = 1040 mAh or 1.04 Ah
To stretch that to 8.5 minutes you need to fly at 8.5/60 x 1.04 = 7.5A average
That's certainly possible. For example, shooting touch and goes, you may use 15A for takeoff, 12A for climb, 9A for the circuit and then chop the throttle for the last part. You can easily get an average of well under 10A, and as little as 7.5A if you are gentle.

On the other hand, some of my friends fly at 20A for most of the flight and use up a 2200 in 5 minutes.

One of them tried it with a 15C 1300 and landed with smoke pouring out and a LiPo pushing the hatch open!
Daedalus66 is online now Find More Posts by Daedalus66
Last edited by Daedalus66; Nov 19, 2012 at 02:37 PM.
Reply With Quote
Old Nov 19, 2012, 02:28 PM
Aussie, Aussie, Aussie!
nrg2go's Avatar
Melbourne, Australia
Joined Apr 2009
1,181 Posts
Quote:
Originally Posted by Aviefly View Post
Wow 8.5 minutes on a 1300
Yep here's a screen shot of a flight on Pushlaris. You can see the batt data at the bottom. There may be a few extra non-working seconds in the total due to me sometimes starting the log before I put it in the water and also stopping the log after I have taken it out.

Name: ImageUploadedByTapatalk1353356756.905901.jpg
Views: 66
Size: 109.0 KB
Description:
nrg2go is online now Find More Posts by nrg2go
Reply With Quote
Old Nov 19, 2012, 03:38 PM
Registered User
Joined Oct 2010
196 Posts
I have a good start on my first polaris from dollar tree foam. I have the nacelle done (maybe built a little too heavy) with a lot of layers of foam. The nacelle has two thicknesses of foam on the sides and three on the bottom. The vertical lower fin has 4 layers of foam, two in the middle and two outside. Boy this foam is not near as ridgid as balsa that I am used to working with. It seems like the motor would pull this thing right apart. I decided to go with two layers of foam for the wing because it was pretty flimsy with one. I put a carbon fiber arrow shaft for the rear spar and will use 1/32" ply for the leading edges.

I am already planing a 75% polaris built as per instructions with dollar tree foam and was wondering if the rear spar needs to be a round tube or could you get away with a flat spar on edge? It seems like it may be just as ridgid or ridgid enough.
flybyjohn is offline Find More Posts by flybyjohn
Reply With Quote
Old Nov 19, 2012, 05:36 PM
Rick
United States, CA, Santa Clara
Joined Mar 2011
1,846 Posts
Quote:
Originally Posted by flybyjohn View Post
I have a good start on my first polaris from dollar tree foam. I have the nacelle done (maybe built a little too heavy) with a lot of layers of foam. The nacelle has two thicknesses of foam on the sides and three on the bottom. The vertical lower fin has 4 layers of foam, two in the middle and two outside. Boy this foam is not near as ridgid as balsa that I am used to working with. It seems like the motor would pull this thing right apart. I decided to go with two layers of foam for the wing because it was pretty flimsy with one. I put a carbon fiber arrow shaft for the rear spar and will use 1/32" ply for the leading edges.

I am already planing a 75% polaris built as per instructions with dollar tree foam and was wondering if the rear spar needs to be a round tube or could you get away with a flat spar on edge? It seems like it may be just as ridgid or ridgid enough.
To ease your concern; My 100% is DT foam. The wing is doubled, which it probably doesn't need except reinforcement at the base of the pylon. Four layers is right for the pylon, one layer for upper fin, one with a bamboo skewer for the stab. The nacelle is doubled all around but probably two sides or top/bottom would be enough. It has taken several hard smacks with no damage/fracture to the nacelle or motor mount. There were some fractures in the wing at the base of the pylon, with a bigger plate here one layer wing would probably be OK. You should double the forward fuse bottom and reinforce the battery tray either double it or put a longitudinal brace under or both. The lower rear fuse should be reinforced per D66's recommendations but doesn't need doubling, nor do the sides or top.

Now that I've gotten used to flying it, the abuse has declined. It flies fine and is plenty strong enough. You can't make it crash proof. PS: I would consider an extra bulkhead in the upper fuse directly over the step. To balance the plane you pinch it there and it's a little soft.
choochoo22 is offline Find More Posts by choochoo22
Reply With Quote
Old Nov 19, 2012, 06:04 PM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
15,936 Posts
Quote:
Originally Posted by choochoo22 View Post
Now that I've gotten used to flying it, the abuse has declined. It flies fine and is plenty strong enough. You can't make it crash proof. PS: I would consider an extra bulkhead in the upper fuse directly over the step. To balance the plane you pinch it there and it's a little soft.
Sounds like a good idea, as long as you don't rely on air flow through the fuselage to cool the ESC. An external heat sink obviates the need for an air scoop. If you do need air flow, you should look at other types of reinforcing, such a couple of pieces of bamboo skewer across the fuselage where you grip it before you put the top on. Lots of possibilities. Just keep it light.
Daedalus66 is online now Find More Posts by Daedalus66
Reply With Quote
Old Nov 19, 2012, 09:12 PM
Rick
United States, CA, Santa Clara
Joined Mar 2011
1,846 Posts
Quote:
Originally Posted by Daedalus66 View Post
Sounds like a good idea, as long as you don't rely on air flow through the fuselage to cool the ESC. An external heat sink obviates the need for an air scoop. If you do need air flow, you should look at other types of reinforcing, such a couple of pieces of bamboo skewer across the fuselage where you grip it before you put the top on. Lots of possibilities. Just keep it light.
Good point! There is always something isn't there? It looks like there is room for both vents in front of the proposed bulkhead though.
choochoo22 is offline Find More Posts by choochoo22
Reply With Quote
Old Nov 20, 2012, 06:04 AM
unconventional :-)
kadil's Avatar
Brisbane north, Australia
Joined Feb 2009
2,114 Posts
Quote:
Originally Posted by nrg2go View Post
Hey Wormboy,

I'll use nothing but 1300's in all my 100% builds!

Of course I use 1300 45C Nanotechs which gives plenty of headroom current wise and keeps the wt right down. I am getting 8:30 flight times out of my setup and putting anywhere between 70-80% back in to them. Speed bores me to tears so throttle position is rarely near full unless doing some high alpha.

Horses for courses I guess but there are valid reasons for everyone's setup. I would never consider using a 2200 but many do for there own reasons.
I agree completely with your approach NRG. Very light model, flying with precision and reasonable power, instead of extreme power is so much more enjoyable for me. I bet that an extremely smooth build has a measurable difference in battery life as well compared to some of my past models.

There are so many ways to fly and mod this design. Awesome.
kadil is online now Find More Posts by kadil
Last edited by kadil; Nov 20, 2012 at 06:09 AM.
Reply With Quote
Old Nov 20, 2012, 06:23 AM
Build, Fly, Rebuild!!
Ghost who walks's Avatar
Australia, NSW, Lake Macquarie
Joined Dec 2011
238 Posts
Battery tray strength

Quote:
Originally Posted by Ramblin View Post
Rather than double the battery tray, i inserted a longitudinal vertical rib between the battery tray and the bottom of the fuse. It requires less material, puts the support directly under the battery and also reinforces the bottom of the fuse.
I did the same with extra bulkhead and vertical longitudinals and can vouch for the effectiveness of the extra strength it adds to the airframe, as you can see from the before and after pictures, this was a nose first smack into terrafirma from a good height (loss of orientation) nose intact even though it took the brunt of the stack.
Now if I can just make the nose removable it might be easier to transport (foldlaris)

PS Hobbyking velcro. battery was still in place!!!

Ghost who walks
Ghost who walks is offline Find More Posts by Ghost who walks
RCG Plus Member
Old Nov 20, 2012, 06:24 AM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
15,936 Posts
Quote:
Originally Posted by kadil View Post
I agree completely with your approach NRG. Very light model, flying with precision and reasonable power, instead of extreme power is so much more enjoyable for me. I bet that an extremely smooth build has a measurable difference in battery life as well compared to some of my past models.

There are so many ways to fly and mod this design. Awesome.
For this sort of flying, it's worth considering the 2212-10 motor (1450KV). It uses a 7x5 prop (or even 8x4 with tips shaved slightly) to give excellent acceleration and climb. The benefit is lower current (about 17A max in the air), meaning you can use a relatively small battery (I use 1500 20C) and still get good flight time. Also, with lower rpm, it's quieter, which is nice for early morning flying at the lake. The down side is less top speed,which may or may not matter.

With such a setup, it's easy to keep the weight to 20oz (560g), which makes for a delightfully light-flying model.

(All of this is not to knock the usual setup with 2200KV motor, 2200 mAh battery and a total weight of 22-23 oz, which will have higher top speed and be slightly less affected by wind. Also, many people already have 2200 batteries.)
Daedalus66 is online now Find More Posts by Daedalus66
Reply With Quote