Aug 30, 2012, 10:53 PM
Registered User
Birmingham (UK)
Joined Sep 2010
345 Posts
Quote:
 Originally Posted by kevinrc It seems to me that power would increase as voltage: 18.5V/14.8V = new power/666W, or 832.5W.
Power does indeed increase when you increase the voltage. However, it increases by more than you expect simply because the current is also increasing.

The actual current values come from measurements with a watt meter, however, what you can be 100% sure of is that if you increase the voltage for any setup, you will also increase the current at the same time. This increase in current is due to the increased load at higher RPM.

That's why you must always make sure you are not exceeding the ESC max current threshold when going from say 4S to 5S.
 Aug 30, 2012, 11:45 PM Registered User Canada, BC, Surrey Joined Jul 2011 948 Posts I can see why all the confusion because mathematically it makes no sense. The missing variable is the load. How does the load increase if the rpm remains the constant value in the equation? The higher voltage will increase with current if the fan rpm also increases. Otherwise if two motors running at the same speed only difference is voltage... The 6s setup will be able to produce the same power or rpm at a lower current than a 4s setup. I really hope this makes sense.
 Aug 31, 2012, 12:09 AM Registered User Joined Aug 2011 828 Posts At the same rpm you are correct the current would be lower. However applying more voltage makes the motor increase rpm hence more load.
 Aug 31, 2012, 12:14 AM Registered User Canada, BC, Surrey Joined Jul 2011 948 Posts agreed, but now we arrive at the point of interest I tried to mention earlier. It seems to me that I could program my throttle curve to limit the load on the motor by noticing at what point in the thottle band I have reached a desirable maximum rpm and make that point the WOT. Last edited by WhalleyB0Y; Aug 31, 2012 at 12:25 AM.
 Aug 31, 2012, 01:23 AM Registered User Joined Aug 2011 828 Posts I do not understand why you would want to do that. The increased weight of the largar battery would counteract the slightly less amp draw. Most people install more cells to increase performance not to try and gain some more runtime.
 Aug 31, 2012, 01:54 AM Registered User Joined Sep 2011 682 Posts @jim350 I agree with you. The only reason I can imagine for running more cells is to get higher performance (rpm). Limiting the throttle curve seems counter productive to me.
 Aug 31, 2012, 09:00 AM Registered User Canada, BC, Surrey Joined Jul 2011 948 Posts Well to be honest, I built a monster. In another thread I am putting together a twin edf that has a lot of power and it got this way because I had oversized everything to be on the safe side. It puts out a combined 3000 Watts at half throttle at a cost of a mere 65 Amps and rather than flying it like a funjet I wanted to know if it was possible to make a more enjoyable flier out of it with a custom throttle curve. A 7lb plane doesn't need 14lbs of thrust but now I have gotten far away from the topic of this thread.
Aug 31, 2012, 11:33 AM
Parkzone junkie
United States, MI, Grand Traverse
Joined Oct 2008
3,769 Posts
Quote:
 Originally Posted by WhalleyB0Y agreed, but now we arrive at the point of interest I tried to mention earlier. It seems to me that I could program my throttle curve to limit the load on the motor by noticing at what point in the thottle band I have reached a desirable maximum rpm and make that point the WOT.
Quote:
 Originally Posted by WhalleyB0Y Well to be honest, I built a monster. In another thread I am putting together a twin edf that has a lot of power and it got this way because I had oversized everything to be on the safe side. It puts out a combined 3000 Watts at half throttle at a cost of a mere 65 Amps and rather than flying it like a funjet I wanted to know if it was possible to make a more enjoyable flier out of it with a custom throttle curve. A 7lb plane doesn't need 14lbs of thrust but now I have gotten far away from the topic of this thread.
Short answer: no this probably will not work.
someone posted a link a page or so back, to Castle ESC FAQ. An ESC sees the max voltage all the time. The ESC is just a switch. so for half throttle you get on-off just a little slower, but during that on phase the ESC better be able to handle the max amps the setup is capable of producing.
Here is the exception: If your 100% throttle WOT amps are within the ESC's ability than it will work.

On the stock Habu the 60A eflite ESC is NOT able to handle 5S WoT which measures 65A-70A. If you switched to a CC75 or 100 than you could, but if you've gone so far to swap ESCs and buy 5S batteries why would you not take advantage of the extra power? It would be cheaper to just buy some 4000mAh 4Cells and get longer flight times that way.

-Brian
Aug 31, 2012, 12:37 PM
United States, CA, Santa Clarita
Joined Aug 2009
9,319 Posts
Quote:
 Originally Posted by WhalleyB0Y I can see why all the confusion because mathematically it makes no sense. The missing variable is the load. How does the load increase if the rpm remains the constant value in the equation? The higher voltage will increase with current if the fan rpm also increases. Otherwise if two motors running at the same speed only difference is voltage... The 6s setup will be able to produce the same power or rpm at a lower current than a 4s setup. I really hope this makes sense.
Here's a factor that hasen't yet mentioned. It's the key to what you are attemping to acomplish...if I read correctly.

To lower your amp draw (and maintain the same power..watts, rpms,by going to a higher cell count (6s in this case)...........You will need to use a motor with a lower kv

Here's how to calculate that.
The stock E-Flite motor is 3600kv.
The motor is being run on 4s
Multiply....motor kv times the cell count.
3600 x 4 = 14400
You want to calculate the kv needed to spin the motor at the same "no load" rpm" for 6s. So divide the sum (14400) by the new cell count. (6)
14400 / 6 = 2400.

The kv required for 6s is 2400. This will lower your amps considerably, and provide the same power you had before.

IF, you reduce the mAh capacity of the lipo to 2400-2500 mAh (for 6s) you will, still have the same flight time, but at lower amps.

IF, you maintain the 3200 mAh capacity. (for 6s) Your flight will be ~25-30% more.

So, now you need a 2400 kv motor.
The closest thing I have is the MEGA 16/25/2, (or the longer 16/40/1.5R) at 2470kv. (you would need a special, with a 4mm shaft, or you migh locate one elswhere) This means the setup will be slightly hotter. (additional speed, at the cost of a few amps more)
Very minimal throttle throttle management will be required to acheive your goal.

Hope that helps, Gary
Last edited by efflux RC; Aug 31, 2012 at 12:43 PM.
 Aug 31, 2012, 01:16 PM Registered User Joined Sep 2011 682 Posts @effluxrc Actually, I THINK the stock motor on the Habu is 3200kv and not 3600kv. I don't know how much of a difference that would make in the equation, but I thought I'd just throw that out there.
Aug 31, 2012, 01:27 PM
Registered User
Canton, Michigan USA
Joined Jul 2007
16,712 Posts
Quote:
 Originally Posted by Mugen4Lfe @effluxrc Actually, I THINK the stock motor on the Habu is 3200kv and not 3600kv. I don't know how much of a difference that would make in the equation, but I thought I'd just throw that out there.

Yes, the Habu motor is 3200 kv. Eflite sells a 3600 KV motor. During development of the first Habu Horizon experiment with the 3600 kv but found it got too hot.
Aug 31, 2012, 02:36 PM
United States, CA, Santa Clarita
Joined Aug 2009
9,319 Posts
Quote:
 Originally Posted by Mugen4Lfe @effluxrc Actually, I THINK the stock motor on the Habu is 3200kv and not 3600kv. I don't know how much of a difference that would make in the equation, but I thought I'd just throw that out there.
Quote:
 Originally Posted by Prof100 Yes, the Habu motor is 3200 kv. Eflite sells a 3600 KV motor. During development of the first Habu Horizon experiment with the 3600 kv but found it got too hot.
I thought it was 3200 in the first place, but when I looked it up. the spec to be sure, the motor here is 3600. I guess they have have 2 different motors that they call the "BL15"
http://www.e-fliterc.com/Products/De...dID=EFLM3015DF

This is the Habu 2 motor.
http://www.horizonhobby.com/products...0kv-EFLM3215DF

You are correct the Habu 2 comes with the 3200kv.

Just change the spec for the 6s motor as discussed above to:

2133 KV
Latest blog entry: Updated blog Oct 2014
Aug 31, 2012, 03:54 PM
Registered User
Canton, Michigan USA
Joined Jul 2007
16,712 Posts
Quote:
 Originally Posted by efflux RC I thought it was 3200 in the first place, but when I looked it up. the spec to be sure, the motor here is 3600. I guess they have have 2 different motors that they call the "BL15" http://www.e-fliterc.com/Products/De...dID=EFLM3015DF This is the Habu 2 motor. http://www.horizonhobby.com/products...0kv-EFLM3215DF You are correct the Habu 2 comes with the 3200kv. Just change the spec for the 6s motor as discussed above to: 2133 KV
Gary,

Yes, Eflite does throw a bit of a curve ball with two motors with the same name have a differnt KV but they do that for some of their outrunners too.

So you are suggesting a 2133 kv motor for a 6S Habu power plant. Do you know anybody who sells them?
Aug 31, 2012, 04:35 PM
United States, CA, Santa Clarita
Joined Aug 2009
9,319 Posts
Quote:
 Originally Posted by Prof100 Gary, Yes, Eflite does throw a bit of a curve ball with two motors with the same name have a differnt KV but they do that for some of their outrunners too. So you are suggesting a 2133 kv motor for a 6S Habu power plant. Do you know anybody who sells them?
Hey Prof,

I knew that answering Walleyboy's question might cause some confusion, so I didn't, (a day ago) but no one esle answered the question he was asking.
His desire is to reduce the amp draw and maintain the same power level, by going to 6s.

Which is motor kv x original cell count dived by the new cell count = the new kv.
....................................

This formula will give you the SAME power. The number is the mathmatical requirement, but you probably find the exact kv motor you need. Look for some thing close, and keep in mind that a bit lower kv will privide lees power, and a higher kv will provide more power (and use more amps)

The MEGA 16/40/1.5S is 2200 kv (getting pretty close)
http://www.effluxrc.com/MEGA-16-35-15-S-MM16-35-15S.htm

.................................................. .........................

Now, as mentioned by some one earlier, most set ups using increased cell counts, do so to provide increased power.
You can use the 2133kv as a baseline for equal power, but you need to go way up from there. There are some motors that are as high as 3200 (or even higher!!) that will take 6s,

Here are some examples of well known 6s, 70mm motors in most 70mm EDF's (forget the CS fan, it will grenade at these levels)

Keep in mind that you can't only go by the KV. Short motors (less mass) will over heat. Longer motors are better.

For 6s. ( lower to higher power)
..............................
HET 2W-25, 2720kv
Velocity V2860-2900...... (1900W)
Mega 16/40/1 (4mm shaft ver) 3150kv
HET 1W-40. 3300kv......(2400W)

The hotter setups reuire a heat sink and possibley some throttle management.

This is only a guide.
The E-flite fan requires a motor with a 4mm shaft.
Latest blog entry: Updated blog Oct 2014
 Aug 31, 2012, 04:43 PM Registered User Joined Sep 2011 682 Posts @effluxrc If the desire is to reduce the amp draw and maintain the same power level, by going to 6s, what would be the reason? To avoid over amping the ESC? IF that's the reason, wouldn't it be cheaper and easier to just upgrade the ESC to a higher amp rating? Sorry, the whole point of all this kind of got lost in my brain!