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Old Feb 01, 2013, 03:28 PM
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Originally Posted by cmdl View Post
thanks dogfly. thats in line with what 19000 and a guy on my field told me so thats what i am looking for while 4s batt shopping.

once my custom mount comes in i'm thinking that maybe the aluminum frame should dissipate some motor heat. and i'll pull the esc out probably all into the cowl. hoping that helps at least on the motor and esc side. of course, bench testing comes first. busy busy busy.
Which motor will you run a 4s on? I am using the stock motor, 9x7.5E prop, 45 amp esc. Motor pulls 37 amps/580 watts and really livened the plane up. This motor may not survive in the summer temps.

I see it's a power 25 1250kv. I have this motor in my multiplex Dogfighter...4s2650 nanotech turnigy, 8x8E prop it does 105 mph. 56 amps/870 watts.
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Old Feb 01, 2013, 03:43 PM
sKrude up, Rejected!
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United States, CA, Santa Barbara
Joined Jun 2008
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Quote:
Originally Posted by cmdl View Post
thanks dogfly. thats in line with what 19000 and a guy on my field told me so thats what i am looking for while 4s batt shopping.

once my custom mount comes in i'm thinking that maybe the aluminum frame should dissipate some motor heat. and i'll pull the esc out probably all into the cowl. hoping that helps at least on the motor and esc side. of course, bench testing comes first. busy busy busy.
cmdl,
Once you get your prop and amps sorted out, you shouldn't have the extreme heat situation.
I don't recomend the aluminum mount, if you crash it transfers the damage to your firewall, I don't think they offer replacement firewalls w/o buying the fuse.
The plastic mts. at least offer a chance for the firewall to survive a crash.
But if your a crash free pilot, or have an unlimited bank account go ahead.
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Old Feb 01, 2013, 03:51 PM
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United States, CA, Rosemead
Joined Jan 2012
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Quote:
Originally Posted by Buster1000 View Post
Which motor will you run a 4s on? I am using the stock motor, 9x7.5E prop, 45 amp esc. Motor pulls 37 amps/580 watts and really livened the plane up. This motor may not survive in the summer temps.

I see it's a power 25 1250kv. I have this motor in my multiplex Dogfighter...4s2650 nanotech turnigy, 8x8E prop it does 105 mph. 56 amps/870 watts.
yep, i'm using the P25 1250kv. still getting around to ordering the 4s batts - likely tonight.

Quote:
Originally Posted by DogFly. View Post
cmdl,
Once you get your prop and amps sorted out, you shouldn't have the extreme heat situation.
I don't recomend the aluminum mount, if you crash it transfers the damage to your firewall, I don't think they offer replacement firewalls w/o buying the fuse.
The plastic mts. at least offer a chance for the firewall to survive a crash.
But if your a crash free pilot, or have an unlimited bank account go ahead.
already ordered the firewall and its shipped so i'll mount it and try it on for a bit. i won't say i'm crash free but more like very low probability. i did have a low intensity crash when i stupidly put a 9x9 on a P15 with 3s powering the setup. she didn't fly very high or far, barely any thrust. cracked motor mount and damaged prop shaft only. of course, that could have been the firewall in different circumstances.
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Old Feb 01, 2013, 05:11 PM
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Cmdl...
This 1250kv motor can be used on 4S, however, 3S would allow larger diameter props which may fly more like you're wanting your spit to fly. As far as picking lipos, the basic rule is not to use more (draw more current), than half of what they're rated for. This protects the ESC and helps make your lipos last longer. My setups never ask more than 35% of my lipos rating, but I fly a lot of WOT!
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Old Feb 01, 2013, 05:15 PM
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LOL. some guys treat their throttle like an on/off switch. hahahahahaha.
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Old Feb 01, 2013, 05:21 PM
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Sure, it takes more skill to use the throttle properly. I just happen to enjoy fast, scale type maneuvers where slow and gradual inputs are required to keep G forces from stressing airframe. I fly slow at first to warm up lipo, then WOT until timer goes off. Love it!
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Old Feb 01, 2013, 05:25 PM
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hey, I'm not knocking you at all. depending on the plane I'm flying, I treat my throttle the same way. LOL.
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Old Feb 01, 2013, 05:37 PM
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Originally Posted by LuvEvolution7 View Post
LOL. some guys treat their throttle like an on/off switch. hahahahahaha.
hey, hey. i'm still going through rehab for not being able to use it as an on/off switch. please don't remind me of that temptation

Quote:
Originally Posted by chudson View Post
Cmdl...
This 1250kv motor can be used on 4S, however, 3S would allow larger diameter props which may fly more like you're wanting your spit to fly. As far as picking lipos, the basic rule is not to use more (draw more current), than half of what they're rated for. This protects the ESC and helps make your lipos last longer. My setups never ask more than 35% of my lipos rating, but I fly a lot of WOT!
all this does seem to tie in to the C rating issue. only thing is, how do i know what batts are rated to pull based on that C rating? and how will i match that up to what the esc demands short of a bench test? for instance, how do you know you're pulling no more than 35%? could you please explain? the only thing i have understood so far is that higher C rating is good for my setups since thebatts are rated for higher discharge and so my low C batts will have to go.

*********************************************

ps - on other news, since my lhs doesn't have the eflite powermeter anyway, i have decided to go with http://www.valuehobby.com/gt-power-130a-wattmeter.html. i'm already planning to order these http://www.valuehobby.com/power-syst...200mah-4s.html from them so a one stop shop is worthwhile at this point.
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Old Feb 01, 2013, 06:05 PM
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well, if you are using 2200 packs for example and you want to pull half of your total Amps that are able to be delivered, you need to do some simple math. 2200 packs are 2.2 amp hours. so, if your Power 25 is able to draw 50 Amps, for example, you need to select a pack capable of delivering double that kind of power. let's take a 45C pack. multiply 45 by 2.2 and you get 99 Amps. that's pretty close to what you want. if you wanna go one step further, try a 60C pack and you get 143 Amps. I think you'll be more than fine with 45C packs, but I use Gens Ace 65C packs. personally, I don't think you are getting too much better when you go from the 45C to the 65C packs, but that's my own experience of course. you'll be happy with the performance on 45C packs and you won't break the bank too badly.
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Old Feb 01, 2013, 06:15 PM
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thanks Luv, that makes sense to me now. very useful example.

ps - one more thing, so i can step down the C rating going 3s to 4s? and how does that factor in?

pps - sheer exhaustion from all the upgrading and ordering led me to take the easy way out and order 3s lipos. 60C gforce elites (i was gonna go with 40C but LuvEvolution's mention of 65C pushed me toward the 60C). i want to try the higher C rating and see how that works out. i can always get the 4s down the line. pulled the trigger on their wattmeter as well. well, at least i don't have to beat my head over props for now. thanks a bunch guys. learned a lot in these past few days thanks to your patience with me. now its time for a breather
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Last edited by cmdl; Feb 01, 2013 at 07:58 PM.
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Old Feb 02, 2013, 01:10 AM
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I wouldn't step down the C rating. I never do anyway. if I use a 45C pack on 3S, I'll generally stick with the same C rating when bumping up a cell. C rating has nothing to do with cell count. it's how much power can be delivered based on the C rating and mAh of the pack.

we can go a step further if you like. this plane could probably handle a larger pack. perhaps 2650 mAh. that being said, if we take the same 45C pack at 2.65 Amp hours, we get 119.25 Amps. this larger pack will be capable of delivering more power, over a longer period of time at the same throttle settings of a typical flight for you. so, rather than upping the C rating, you can simply increase the gas in the tank, so to speak.

so we can take that a step further. if you were using a 25C, 2200 pack, your Power 25 is still drawing 50 Amps, as in our previous example, but your pack is only capable of 55 Amps. your pack is on the ragged edge and therefore will either get hot and/or get puffy very quickly. to make life simpler and easier for your packs, you would need to bump up to at least 4000 mAh packs. at 4 Amp hours, you would get 4 x 25 = 100 Amps. that would be much better, but a 4000 mAh pack might be too heavy for the plane.

at least now you understand how to do the math and then figure out what packs to buy, also based on how much they weigh. the nice thing about Hobby King and many other places, is that they put the weights of their packs on their sites.

Rich
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Old Feb 02, 2013, 03:02 AM
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Cmdl...sorry about the formatting

Sent you two PM covering what Rich just covered only trying to explain the why as well...

some calculator values...
for a 75% efficient, 1250kv, 800 watt motor...

Following values are WOT in the air, not static.

stock 950kv motor on 3S with stock 9.5x7.5x2 prop:
9.5x7.5x2 19 amps 56 pitch speed 32 oz thrust
(guessed at this, calculator database doesn't have this prop)

75% efficient, 1250kv, 800 watt motor will:
(depending on lipo volt, capacity, C rating, model drag, motor eff, other factors; don't know how to convert pitch speed into actual mph; mph is xx% less ??, but it's bound to be a non linear variable and certainly model dependent; (radar gun, GPS could help!!))

on 3S...
APC 9x6x2 27 amps 58 pitch speed 43 oz thrust
APC 9x7.5x2 35 amps 72 pitch speed 45 oz thrust
APC 10x7x2 41 amps 67 pitch speed 56 oz thrust
APC 10x10x2 58 amps 96 pitch speed 56 oz thrust
APC 11x5.5x2 47 amps 53 pitch speed 61 oz thrust
APC 11x7x2 57 amps 67 pitch speed 74 oz thrust

on 4S...
APC 8x6x2 33 amps 77 pitch speed 53 oz thrust
APC 8x8x2 45 amps 102 pitch speed 54 oz thrust
APC 9x4.5x2 35 amps 58 pitch speed 56 oz thrust
APC 9x6x2 47 amps 77 pitch speed 75 oz thrust
APC 9x7.5x2 62 amps 96 pitch speed 79 oz thrust

Notice how the 9x7.5 on 3S has similar specs to the 8x6 on 4S. There is no way I know of to figure out how a prop will fly my plane except to try it.

I'm always surprised at the differences when trying various props. Have almost no experience with 3 and 4 blade props, but I'll eventually get around to trying them.

Lipos can be the weak link when comparing props if the voltage goes down too much as the current goes up. I try to minimize these factors by not asking much from my lipos.

Going to buy my first 45C lipos next week and can't wait to see how much difference they'll make. At least they'll be new and not have over 200 cycles on them.
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Old Feb 02, 2013, 09:46 AM
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the only difference I've noticed, is that they give higher power for roughly about the same amount of time. in other words, there's less drop off than in lower C rated packs. I have not noticed any difference between 45C and the 5C packs. my EDF's give the same performance with either pack. there's a huge difference between a 30C and a 45C pack though, but for whatever reason, the 65c behaves the same way a 45C does. weird eh!?

Rich
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Old Feb 02, 2013, 10:27 AM
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Suppose as long as the battery can give the motor/esc the required ampage then any extra power that you gain having a bigger C rating, therefore better voltage under load, is offset by the extra weight?


Tony
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Old Feb 02, 2013, 11:02 AM
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Originally Posted by SilentPilot View Post
Suppose as long as the battery can give the motor/esc the required ampage then any extra power that you gain having a bigger C rating, therefore better voltage under load, is offset by the extra weight?


Tony
The higher the 'C-rating', the higher peak current a pack can tolerate delivering and sustaining, without damaging itself.

In general, the higher the 'C-rating' of a pack (all else being equal) ... the lower its internal resistance, thus the lower the proportion of available voltage is lost internally across pack terminals (under a particular external load)
... consequently a slighly higher voltage is delivered to the motor; this obviosly results in a slighly higher current too.

This is why a motor seems to have slighly more power on the higher C-rated of two packs, even though they might be advertised as the same (say) 3s, 11.1 Voltage.

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