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AEAJR 04-15-2007 09:37 PM

Selecting Electric Power Systems -
 
SELECTING ELECTRIC POWER SYSTEMS
Reference Resources

Electric airplanes can be lots of fun and very little work. There are lots of
RTF planes
that already have their power systems selected and installed. They require no
work at all on your part. That is about as easy as it gets.

If you like ARFs or kits, many come with motors and props standard. Some will
include a gearbox as well, if the designer considers that the best approach.
While these may not be the most powerful motors you might put on the plane, you
can be reasonably confident that they will fly the plane. The instructions will
normally recommend an appropriate sized electronic speed control, ESC, and
battery pack to use with that motor and propeller combination on that plane.
Just read the friendly manual, RTFM, and you can usually get the plane in the
air with little trouble. That is still pretty easy.

But what if you want to design a power system yourself. Perhaps you are
converting a glow or gas plane over to electric power. How would you go about
doing something like this. This is not a trivial task. There are many factors
to take into consideration and there are hundreds of motor, ESC and battery
pack options out there. How do you choose?

Or say you want something better or stronger than the motor that came with your
plane? And, of course, some ARFs and kits don't include motors. And finally
there is the fun of designing your own planes. Now you need to plan the power
systems.

If you are going to design your own systems you will need some help and some
knowledge. What I have compiled is a list of links that take you to resources
to help you. First I recommend you read this article for background
information. It will help you understand and use the rest of the resources
listed below.

Sizing Electric Power Systems -
http://www.ampaviators.com/index.php?option=com_content&task=view&id=41&Itemi d=27

Remember that the system operates as a whole. If you have the right motor
with the right battery and put on the wrong prop, things can get pretty ugly
pretty fast.

I highly recommend you pick up a wattmeter. If you are going to be a designer
there are only two ways to know if you got it right. The first is to measure
the
amps, volts, watts being drawn by your new power system and making sure all
components are up to the effort. The other way is to see the plane fly badly,
watch your new motor burn up, your new battery pack fail or see the magic smoke
come out of your ESC. Personally I would rather you get a wattmeter. This
thread discusses their value and uses. Several are discussed.

WATTMETERS - Vital to the power system designer
http://www.wattflyer.com/forums/showthread.php?t=11863


Brushed vs. Brushless motors

Many RTF, ARF and Kits come with brushed motors. These are often identified by
a "speed:" designation such as speed 280, speed 370, speed 400, speed 600 and so
on. They work fine but are less powerful and less efficient than brushless
motors. If you are going to design your own power systems I suggest you go
directly to the brushless motors. Prices have come down a lot and quality, even
at the low end, is good. So leave the world of brushed motors behind and go
brushless. From this point forward I will only be looking at brushless systems.

Resources

Some manufacturers have done a good job of providing tables and charts that can
help you use their components to come up with the right system. Armed with the
knowledge from the first article you are now better equipped to use them. The
ones I have found most useful are next.

MAXX PRODUCTS

Maxx Products - How to Choose a Brushless Motor for an Airplane
pretty good tip sheet on coming up with a glow to electric power comparison.
http://www.maxxprod.com/mpi/tips3.html
HiMaxPower System Packaged sets and info chart
Motor, speed control and prop all matched up for you
http://www.maxxprod.com/mpi/mpi-264.html


ELECTRIFLY

Guide to Glow to Electric Conversions
http://www.electrifly.com/manuals/gpmz0010-glow-to-elec-conv.pdf
Electrifly Electric Motor Configuration Tool
It assumes you know where you are going. Read the article above and you will be
better prepared to use this too.
http://www.electrifly.com/config/
Brushed motor to Brushless Motor Conversion Chart
The recommendations will yield a significant power boost.
http://www.electrifly.com/powersystem/brushed-to-brushless.html
Chart of Sample Planes and Recommended Power Packages
http://www.electrifly.com/powersystem/specific-plane-conversions.html
Electrifly Brushless Brochure. Lots of useful info that you can print out.
It is only for Electrifly components, but it is well done.
http://www.electrifly.com/sellsheets/power-system-brochure.pdf

GWS

GWS provides excellent information about their brushless motors and how they
perform with different batteries, and props. Useful, once you understand the
watts/pound rules.
http://www.gwsus.com/english/product/auxcircuit/brushless.htm

Other Resources

A series of posts on electric power system basics
http://www.wattflyer.com/forums/showthread.php?t=1933
http://www.rcgroups.com/forums/showthread.php?t=417868

MotoCalc will tell you everything you need to know: Amps, Volts, Watts, RPM,
Thrust, Rate of Climb, and much more! It is a popular tool for predicting the
proper motor, prop, battery pack for electric planes. Read the first article
first and this will make a lot more sense.
http://www.motocalc.com/

Amps vs. Volts vs. C
http://www.ampaviators.com/index.php?option=com_content&task=view&id=37&Itemi d=27

Low Voltage Cutoff
http://www.wattflyer.com/forums/showthread.php?t=3445

Milton 04-19-2007 06:52 PM

It is all about watts, Watts are power.

I use this to decide what type set up to use

100 watts to pound for good heavy sports flying
125-135 good aerobatic
150 and up for aerobatic and 3D type plane

Now what makes watts, amps X volts = watts

I like large planes so lets look at a 20 pound all up weight sports plane

Looking for 2000 watts, Knowing that I want 2000 watts and saying I will run a 10S lipo ( higher voltage is better than higher amps)

With a good battery I should hold around 35 volts under a load so now I will put 35 volts into 2000 watts = 57.14 amps. That tells me I need a motor that will handle 35 volts and about 60 amps.

There is another thing to look at, You have watts in and watts out, Or the amount of fuel you put into the system to what kind of power you get out of it.

You will see different efficiency ratings, I have seen them that was rated as high as 92-95%. That is hog wash, There are not many out there that go above 85% most are around 80%

So lets go with 85%
If 746 watts = 1 HP

So I will be putting in 2000 watts divided by 746 = 2.68 HP
That is power in now for power out I will take that times 85% ( efficiency)
2.68 times 85% = 2.27 HP.

Milton

Razmo 04-19-2007 08:43 PM

This thread looks promising. I actually came here to post a question about "Understanding and choosing a power plant". Looks as if this may be the place to start...

Thanks,
Raz

AEAJR 04-19-2007 09:33 PM

Milton, great post!

Razmo 05-02-2007 01:26 AM

Quick question...

To confirm, when sizing up an appropriate powerplant using the 50,75,100, etc Watt guidline. I'm including motor, battery, esc and etc, YES? ("ALL UP WEIGHT")

Raz

Milton 05-02-2007 01:58 AM

Yes, All up wieght.
You will just have to guess at it with what you think you will use to set it up.
I am alway's a little over when I finish a set up.

Milton




Originally Posted by Razmo (Post 190064)
Quick question...

To confirm, when sizing up an appropriate powerplant using the 50,75,100, etc Watt guidline. I'm including motor, battery, esc and etc, YES? ("ALL UP WEIGHT")

Raz


AEAJR 05-02-2007 02:32 AM

This is not an extremely exact science. +/- 10% in weight is not going to matter. Even 20% if you are not tyring to size it too close. When in doubt go for a little higer power to weight ratio unless you are trying to go very light, like an indoor flyer.

Razmo 05-02-2007 04:01 AM

I'm questioning because I recently had a Husky model built for me that came out at 13oz *all up weight*. According to the formula, I need a 40watt motor.

The vendor suggested a Himax 30watt motor (designed for 11.1v) which is rated for models between 6 to 8 ounces. This what the model is currently equipped with. (I haven't flown her yet) She is a float plane.

I'm thinking I may be better off with the Himax 50watt motor (designed for 7.4v).

Raz

TRASHBUG 05-02-2007 11:49 AM


Originally Posted by Razmo (Post 190140)
I'm questioning because I recently had a Husky model built for me that came out at 13oz *all up weight*. According to the formula, I need a 40watt motor.

The vendor suggested a Himax 30watt motor (designed for 11.1v) which is rated for models between 6 to 8 ounces. This what the model is currently equipped with. (I haven't flown her yet) She is a float plane.

I'm thinking I may be better off with the Himax 50watt motor (designed for 7.4v).

Raz

Personally, I'd figure a minimum 100 watts per pound for a float plane. It's tougher to get off the water than a blacktop parking lot. 13 oz plane = 80 watts.

LOL

skiman762 05-02-2007 12:22 PM

Doe that mean a 25oz 600watt wing is way over powered or just way too much fun:Q :) :< :ws:

AEAJR 05-02-2007 01:45 PM


Originally Posted by Razmo (Post 190140)
I'm questioning because I recently had a Husky model built for me that came out at 13oz *all up weight*. According to the formula, I need a 40watt motor.

The vendor suggested a Himax 30watt motor (designed for 11.1v) which is rated for models between 6 to 8 ounces. This what the model is currently equipped with. (I haven't flown her yet) She is a float plane.

I'm thinking I may be better off with the Himax 50watt motor (designed for 7.4v).

Raz

You have two choices.

Try what you have and see how it does or take it apart before you try it and never know.

I would try it and see, unless you plan to send it back to the builder for a redo.

These guidelines are very broad. After all, what is "scale flight" and what is "sport" and what is "agressive aerobatics"? It is all very subjective.

These are starting points. My Aerobird Challenger flies quite nicely at 48 watts per pound but it will never be a pattern plane. My Easy Glider Electric climbs very agressively at 90 watts per pound, but I usually climb at 3/4 throttle because it uses less power and is more efficient.

Your float plane may do fine at the 38 watts/pound of the current set-up. Try it!

A large influence will be the propeller. If you are propped for thrust vs speed, you may be perfectly balanced in your current configuration for scale flight with an occasional loop. After all, float planes are not generally flown through agressive patterns. ;)

Fly it, you may like it! ;-)

AEAJR 09-09-2007 02:52 AM

I revised the example part of the original post, so I thought I would provide the updated part here.

AN EXAMPLE!

This should be fun. Let's see where these formulas take us! We will use a
24 ounce, 1.5 pound plane as our example. If we want basic flight you will
need 50 watts per pound or about 75 watts input to your motor for this 1.5
pound plane. That is, 50 watts per pound X 1.5 pounds = 75 watts needed
for basic flying performance. If you want a little more spirited plane, we
could use 75 watts X 1.5 pounds which is about 112.5 watts.

Lets use 100 watts as the total target, just to be simple, shall we? I am
going to use a lot of round numbers here. I hope you can follow.


The Battery
If we use an 8 cell NiMh battery pack at 9.6 V it will have to deliver 10.4
amps to hit our 100 watts input target ( 100/9.6 = 10.41amps) If my
battery pack cells are NiMh cells that are rated at 10C then I need an 8
cell pack rated at 1100 mah to be able to deliver 11 amps. Sounds about
right.

Now I select a motor that can handle 100 watts or about 10.4 amps at 9.6
Volts. From experience we know this could be a speed 400, a speed 480 or
some kind of a brushless motor.

We now need a propeller that will cause the motor to draw about 100 watts. I
don't know off the top of my head what that would be. I would go to some mfg
chart as a starting point. GWS has good charts!
http://www.gwsus.com/english/product/powersystem/edp400.htm

I see that if I use a direct drive speed 400 with a 5X4.3 prop at 9.6V then
the motor will draw about 12.4 amps or about 119 watts. This would be a
good candidate motor/prop for the plane using a 9.6V pack that can put out
12.4 or more amps. This would be a set-up for a fast plane as that motor
will spin that small prop very fast.

However maybe I don't want such a fast plane but one with a really good
climb and lots of low end pull to help out a new pilot who is in training or
to do more low speed aerobatics

I can also use a speed 400 with a 2.38 gearbox and run it at 9.6V spinning a
9X7 prop and run at about 12.8 amps for 120 watts.
http://www.gwsus.com/english/product/powersystem/eps400c.htm
The larger prop will give this plane a strong climb, but since the prop
speed has been reduced by 2.38 times, it won't be as fast. Spinning a
bigger prop gives me more thrust but a lower top speed typically. This is a
common strategy for 3D planes.

Back to battery packs and motors

So if I shop for a 9.6V pack to be able to handle about 15-20 amps, I should
do just fine and not over stress the batteries. In NiMh that would probably

be a 2/3 or 4/5 A pack of about 1000 -1300 mah capacity. Some examples here: http://www.cheapbatterypacks.com/mai...ells&chem=NIMH

We view the battery and motor as a linked unit with a target power profile,
in this case about 100 watts. We use the prop and gearbox, if any, to
produce the manner in which we want to deliver that power to the air to
pull/push the plane.

If this is a pusher, I may not have clearance to spin that big prop so I
may have to go for the smaller but faster prop combo.

If this is a puller, then I can choose my prop by ground clearance or some
other criteria and match a gear box to it.


See, that was easy, right? ( well sorta but ....)


But we are not done! Oh no!

I could try to do it with a 2 cell lithium pack rated 7.4V. To get 100 watts
I now need a pack that can deliver 13.5 amps and a motor/prop combination
that will draw that much. So if I have 10 C rated lithiums, then the pack
better be at least 1350 mah. Probably use a 1500 mah pack to be safe.

Well, when I look at the chart for the geared speed 400 I see that,
regardless of prop, at 7.4V I am not going to have enough voltage (
pressure) to push 13 amps into this motor. So the 2 cell lithium won't meet
my performance goal of 100 watts+ per pound using this gear box.

If I go back to the charts and look at a different gear boxes. I can't hit my
power goals using 7.4V. Maybe we go back to direct drive.
http://www.gwsus.com/english/product...tem/edp400.htm

We see that the best I can get this speed 400 to do is a total of 70 watts
at 7.2V ( close enough ) so I can't hit my power goals using a speed 400 at
this voltage. but 70 watts would be about 48 watts per pound so I could have
a flyable plane, but not an aerobatic plane using this two cell pack.


REALITY CHECK!

Now, in fact that is NOT how I would do this. I would decide on the watt
target, go to the chart, find a combo that meets my goals, then select a
battery that will meet the demand and see if my weight comes up at the
target I set. A little tuning and I come up with a workable combo.

I often use the MaxxProd combos for reference. If you read the details on each
package they have wonderful information. And, the fact is that I generally go
with brushelss motors these days. Costs are reasonable and their higher efficency
gives me more performance and longer flight times.
http://www.maxxprod.com/mpi/mpi-264.html

Following the example above, the combo 10 on that page would be an excellent
fit for my 1.5 pound plane for sport flying.

The Combo 049 might be a good fit for a slow flyer. Either way the package
has all I need.

If I wanted the plane to have all out performance, the 15A or 19A package would
be my pick. Note that these would need either higher voltage or higher amperage
battery packs. The flyers/PDF for the packages make recommendations.

For those who like to be even more analytical about it, there are packages
like MotoCalc that will allow me to play with all sorts of combinations and
make suggestions on what I should use. There is a link for MotoCalc below.


SUMMARY

So, in these few paragraphs you have taken in a basic knowledge of how electric
power systems are sized, the factors that are considered an how to predict
the outcome. Simple, right?

Of course there is a lot more to know and time and experience will teach
you plenty, but with this basic understanding you are better prepared to
begin playing with the power systems you put in your planes.

Grumman 10-08-2007 08:12 PM

New White Eagle Multiplex Twin Jet (Battery Suggestion)
 
Hello!!! Can any suggest to me a battery for my new Multiplex Twin Jet, it will arrive with 2 X Permax 480 Brushed Motors. I have heard everything from the rated voltage of 7.2 volts all the way up to 12 volts for these motors and now I am a bit confused, how is it possible to run a 7.2 volt motor on 12 volts and not destroy it???
I will buy Li-Po or nimh I have several chargers on hand... The manufacturer suggest a 7.2 nimh 1700 battery I believe... I understand it will come with Gunther Props and I have also heard that they spin off at times so I ordered some APC 5 X 5.5's and colet type mounting units. I would like to get a little more duration and power from the battery choice so I am prepared to spend whatever it takes to power this new Jet properly.... If any of you guys have any good information and your suggestions would be of great assistance to me I will look forward to your advice...
Thank You in advance for your time...
Happy Flying!!!
Maurice????

AEAJR 10-08-2007 10:18 PM

I am a very big beliver in reading the instructions first.
http://www.multiplexusa.com/product_fs.htm

According to the Multiplex those are 400s, not 480s. If you are upgrading them, you should say so.
http://www.multiplexusa.com/product_fs.htm

On page 8 the battery recommendation is for 7 cell Sub C cells. That means 8.4V and able to feed a lot of amps.

Assuming you plan to upgrade to 480s, they recommend you go to an 8 cell 9.6V pack

The first question is what kind of amperage are those motors going to pull? I am going to guess about 40 amps between the two motors.

So a 3 cell 2500 mah rated at 20C or higher should work fine. You could go to 3000 mah if you like. That will give you higher voltage and more capacity at lower weight. But the 3 cell Lipo might burn out the brushes on the motors.

If that happens, you go to twin brushless for REAL power and speed!

Grumman 10-08-2007 10:37 PM


Originally Posted by AEAJR (Post 286298)
I am a very big beliver in reading the instructions first.
http://www.multiplexusa.com/product_fs.htm

According to the Multiplex those are 400s, not 480s. If you are upgrading them, you should say so.
http://www.multiplexusa.com/product_fs.htm

On page 8 the battery recommendation is for 7 cell Sub C cells. That means 8.4V and able to feed a lot of amps.

Assuming you plan to upgrade to 480s, they recommend you go to an 8 cell 9.6V pack

The first question is what kind of amperage are those motors going to pull? I am going to guess about 40 amps between the two motors.

So a 3 cell 2500 mah rated at 20C or higher should work fine. You could go to 3000 mah if you like. That will give you higher voltage and more capacity at lower weight. But the 3 cell Lipo might burn out the brushes on the motors.

If that happens, you go to twin brushless for REAL power and speed!

Thank you for your reply ED. Here is the spec list from where I purchased the TwinJet...
<TABLE width="100%" border=0><TBODY><TR><TD class=contentsTopics>BBK Twin-Jet 480 Racers Edition White Eagle</TD><TD align=right></TD></TR></TBODY></TABLE>Multiplex
Product No.: 002344
Print product data sheethttp://www.natterer-modellbau.de/pro...lish/print.gif
Frage zum Produkt http://www.natterer-modellbau.de/pro...a_question.gif <!-- <table width="200" border="0" cellpadding="0" cellspacing="0"> <tr valign="middle"> <td class="main">Shipping time:</td> <td class="main">1-3 Days</td> </tr> </table> --><TABLE width="100%" border=0><TBODY><TR><TD style="BORDER-RIGHT: #cccccc 1px solid; BORDER-LEFT-COLOR: #cccccc; BORDER-BOTTOM-COLOR: #cccccc; BORDER-TOP-COLOR: #cccccc" vAlign=top align=middle><TABLE cellSpacing=0 cellPadding=0 width=1 border=0><TBODY><TR><TD align=middle><TABLE cellSpacing=0 cellPadding=5 width=1 border=0><TBODY><TR><TD>http://www.natterer-modellbau.de/pro...ges/2128_0.jpg</TD></TR><!-- more images --><!-- more images eof --></TBODY></TABLE>
</TD></TR></TBODY></TABLE></TD><TD class=main vAlign=top>If you can handle a TwinStar with confi dence, this model is your ideal fi rst step into the “world of jets”. Hand-launching is straightforward,
and the model is easy to land.
The Twin-Jet is also extremely robust due to the use of ELAPOR® foam, making it a good choice for the relatively inexperienced flyer.
Its strengths lie in elegant low passes, rolls and loops, while the sound of the twin electric motors is very impressive.

• Endless upgrade potential
• Low-cost NiMH sub-C fl ight batteries
• Final assembly in around two hours
• Straightforward hand-launching - no assistant or catapult required
• Reduced crash risk through the use of resilient ELAPOR®
• Two Permax 480 motors, propellers and cable set included

Contents:
• Moulded ELAPOR® foam components
• All small items required
• Two Permax 480 motors and cable set
• Two propellers
• Decal sheet
• Instructions

Specifi cation:
Wingspan: 910 mm
Fuselage length: 802 mm
Weight, standard: min. approx. 1000 g
Weight, upgraded version: min. approx. 1100 g
Wing area approx.: 25.5 dm²
Wing loading: min. 36 g / dm²
Functions: A, E, T (delta mixer required)</TD></TR></TBODY></TABLE>
Thanks again Ed,
Maurice

AEAJR 10-22-2007 06:13 PM

Sorry I have not responded. Must have overlooked the notification.

So, what battery does the mfg suggest? Since the specs I found say it has 400s I am hesitant to respond. But again, based on my earlier post, if you assume 40 amps you will probably be fine.

What ESC do they recommend?

You ordered it, I presume you have it by now. What have you done with it? If you share the outcome here, others will benefit.

Grumman 10-22-2007 08:07 PM

Hello Ed!!! The Jet did arrive and it did come with Twin Permax 480 motors. I was reading some of the guys post in Pusher Delta's and decided to go with a Li-Po Pack...3200 3s2p Li-Po The Mfgr. suggest a NiMh 1700 pack... I have seen some clips with the plane flying with this pack and yes it flies fine but it's a bit slow... I have read a post where someone has the 480's with the 3s2p pack and all is fine.... I work on a ship and we just left the Porto Sole in Italy so I haven't had a moment to try anything, as soon as I can I will post all findings and readings...
Thank You Ed
Happy Flying
Mojo

AEAJR 10-22-2007 08:52 PM

Good thing it is foam, should it happen to land in the water. ;D

Grumman 10-22-2007 09:30 PM


Originally Posted by AEAJR (Post 293501)
Good thing it is foam, should it happen to land in the water. ;D

That's Right Ed!!! I will check in as soon as I have some #'s to report...
Great Thread, lot's of good info...Thanks
Happy Flying
Mojo

arniep 11-09-2007 08:42 PM

For being a relative newbie, can anyone tell me what brushless motor would I use in place of a brushed Speed 400?

For example, the Overlord http://www.edgerc.com/overlord.htm says to use a speed 400 but I want to substitute a BL motor. Can anyone explain how I would find a suitable BL motor?

Thanks....arniep

AEAJR 11-10-2007 04:14 AM

First thing you do it read the article. Then you come to understand that watts per pound is a leading indicatior of how ot match your motor to your plane.

So, what watts per pound target are you looking for?

arniep 11-12-2007 12:37 AM

I think 75 watts per pound should do it. I am not a speed demon and actually enjoy slow flight with the ability to do some maneuvers.
Thanks...arniep


Originally Posted by AEAJR (Post 301619)
First thing you do it read the article. Then you come to understand that watts per pound is a leading indicatior of how ot match your motor to your plane.

So, what watts per pound target are you looking for?


III Bones Air Force 12-16-2007 03:07 PM

Should I change battery, propeller, OR both
 
Hello all: Great thread, my knowledge about power systems grew exponentially reading this thread. I have subscribed to this thread to see if I can find anwers to the following scenario:

I have scratch built a NASTY foamy with 34" wing span and total weight of 13.4 Oz. Electronics, battery and set up as follows:

Motor: BP 8Y brushless Rated at 10.9 Amp- see specs. at this link http://www.bphobbies.com/view.asp?id...97&pid=V615640

ECS: Castle Creation 18 AMP 2s, and 3S auto detect.

Battery: DN Power 900 MAH 2s Lipo (7.4 V) - Rated at 10C. I also have acquired but not yet used a 16 C 7.4 Thunder Power with 1320 mah.

My NASTY flies great with Rudder, Elevator, and aileron.

Propeller: 1041.

Great take offs and great handling, must always have throttle input to keep in air, otherwise it drops quicker than I would like. Maybe because it is flat.

Anyhow, the main problem I have with my set up is the flight duration. It is short, I have not exactly measured it since I just started flying it, but it is much less than the 8 - 12 minutes I was hoping for. I am guessing the battery's mah rating is low OR the voltage could be higher, or the Battery's C rating could use a boost. I do have MR Power Analyzer II that I just got. any help would be great on how I might be able to "fix" the flight duration on this set up and increase it. I know I must think in terms of the whole system, however, at this stage the only variables I am looking at "playing" with are: Battery, and/or the propeller.

Any help would be great. Thanks,

AEAJR 12-16-2007 05:21 PM

You must measure the voltage under load and the amperage being drawn by your set-up. A wattmeter is the most convenient way to do that. I don't know the MR Power Analyzer, but I presume that is what it is for.

Assming you are pulling 9 amps, the maximum your lipo pack is rated for, it should give you about 6 minutes at full throttle and the lipo will be working at its limit, which will not give you maximum lifespan for the pack.

Assuming 9 amps at 7.5V, that would be 67 watts or about 82 watts per pound. That should give you great performance.

If you are pulling 10 amps, you are overstressing the pack and will get less than 6 minutes. duration and very few flights before the battery degrades.

If you are going to design your own power systems you MUST measure it. You have the tool. Let us know what you get when you measure.

III Bones Air Force 12-17-2007 07:42 PM

Thanks Ed. I am planning on doing some measurments as soon as the temp climbs above 20. It's been brutal around here. I want to try and check the bench top measurmnents shortly before I take it out for a spin with the Thunder Power and again with the DN Power batteries.

The Medusa Research is a basic wattmeter that seems to work very well. Again thanks.

AEAJR 12-17-2007 08:17 PM


Originally Posted by arniep (Post 302538)
I think 75 watts per pound should do it. I am not a speed demon and actually enjoy slow flight with the ability to do some maneuvers.
Thanks...arniep

arniep,

What motor did you finally choose, or are you still thinking about this? If you are still looking for advice, let us know.

You never said how much the plane weighed or what battery you were planning to use, so I will take some guesses. I will assume a 1 pound plane and 3 cell lipo is your target pack. So a 75 watt set-up should work.

Take a look at the combo 061 on this page.

This is a 90 watt package
http://www.maxxprod.com/mpi/mpi-264.html

I have one of these in my Mountain Models SmoothE and am very happy with it. You will need a 3 cell Lipo or 8 cell NiMh pack that can handle about 10 amps. I use a 3 cell 1250 15C pack from FMADirect.

mred 01-02-2008 12:16 AM

Need some help with motor replacement
 
I need a little help with a motor. I have this plane, Ultrafly Outrage-3D that I am in need of a motor. It calls for an Ultrafly B/06/10. I had it in my shopping cart at Tower, but got side tracked for a few days and when I came back, it was gone. I mean gone forever. It's not even listed on the Ultrafly site as a motor they make anymore. I guess it was on sale to git rid of the few they had left and now I am out of a motor. I don't know what to replace it with because I don't know anything about the motor to begin with. While I have been flying for awhile, I am kind of new to elect. planes and only have a couple now. Love my Super Sportster with a brushless motor in it. Way over powered, but love it to death. 450 Watt motor with a 4000mah 3 cell LiPo battery with a 9x6 prop and boy does it fly great. I'm not insane for power on all my planes though, just some of them. Anyway, any help sure would make my life easier. Thanks.
Ed

AEAJR 01-02-2008 02:47 AM

I presume you read the first post and the one just before yours. So what help do yo uneed?

You know about watts and watts per pound. How can I help you. I don't track every plane and motor made.

adwb 01-08-2008 08:49 PM

missing link help please
 
Please can any one tell me how to use this link in the 1st post in this thread
thank you
Alistair

"First I recommend you read this article for background
information. It will help you understand and use the rest of the resources
listed below.

Sizing Electric Power Systems -
http://www.rccyberflyer.com/forum/showthread.php?t=272"

AEAJR 01-08-2008 10:06 PM

Thanks for letting me know about this. I think that site just closed down. Try this:

http://www.ampaviators.com/index.php?option=com_content&task=view&id=41&Itemi d=27

I updated the link in the first post.

Bob Vollaro 01-11-2008 04:50 PM

Thanks to AEAJR ON SELECTING ELECTRIC POWER SYSTEMS
 
I attended my first club meeting last night. The topic was"how do I know what system to use" I'm new to RC so I'm trying to soak-up as much knowledge as possible on power systems. AEAJR's intoduction and related web sites was excellant! I'll pass it along to members (Flying Tigers AMA club #3937):) The sport needs more of this type Info. for folks just getting into Electrics. THANK YOU AEAJR

AEAJR 01-11-2008 05:56 PM

Glad to help. I have been approached by a number of people who want to repost that. Feel free to distribute. Tell them to post questions and comments here so those questions and answers can add to the knowledge captured in this thread.

Mike Anderson 01-18-2008 02:23 AM

Watts / Lb at the Extreme
 
I'm coming late to this party but thougt that an article I wrote for our Model Aeronautics Association of Canada (MAAC) magazine last April, would fit rather nicely here:

Extreme Electric Flight
Mike Anderson©

In July 1987, Keith Shaw proposed a few new rules of thumb for electric flight in his Electric Sport Scale article published in Model Builder magazine. For sport aerobatics you needed 40 to 60 watts per pound from the battery and you’d need 70 to 100 W/lb for "good" aerobatics. In the electric flight world of 1987, the best motors were DC (brushed) with cobalt magnets and could deliver 75% of the battery’s power to the prop. Big, high current batteries were 1750 mAh NiCd cells that get you a 3 and a half-minute flight at 30 amps. Now fast-forward twenty years.

The latest generation of LiPoly batteries are rated to deliver 50C currents for short bursts of 3 to 5 seconds and with capacities around 5000 mAh, that means 250 amps to the motor. The latest AC (brushless) motors can deliver 90% to 95% of that power to the prop. Nowhere do these two facts work best together than at the extreme performance end of electric flight; F5B, AKA racing gliders.

Visit the FAI website (www.fai.org/aeromodelling) and you’ll soon discover that F5B competition rewards planes, pilots and equipment that climb the fastest and fly the fastest. Pilots fly laps between pylons with the motor off, but need extreme power to climb to height again to re-enter the course. They can make no more than 10 climbs in 200 seconds to about 400 to 600 feet altitude and they want to be going FAST when they enter the course, snap off their motors and fold their props in tight for a gliding speed run. When that’s all over they climb one last time to glide before making a spot landing exactly ten minutes later.

Wings and tails are hollow-moulded in composite structures of carbon fibre, kevlar & fibreglass, producing a thin, tough wing that can slice through the air like a Samurai sword. Fuselages are moulded in different combinations of the same materials. An empty airframe weight of 650 grams would be considered heavy.

At the last F5B world championships held summer 2006 in Pitesti, Czech Republic, world class F5Bers were pulling over 250 to 300 amps for 3 second bursts out of 16 NiMH cells that were delivering power in the 500 W/lb range. Climb rates were close to 10,000 feet per minute and velocity entering the course would be in the 130 to 150 MPH range. Many teams showed up with dozens of 16 cell packs, many with the intention of flying the pack once then trashing it, knowing that the abuse of a single flight would render them useless for further competition. Several competitors simply pushed too hard and had packs either venting or popping cells in flight. Speed controllers were overheating and planes were seen trailing smoke.

At this level of competition, F5B has become the Grand Prix of aeromodelling sport. The FAI will be considering rule changes to reduce the competitive pursuit of power-at-any-cost, by installing a watt-minute limiter on every plane. In its simplest terms they are fixing the size of the gas tank. You can burn all your watts at once, or pace yourself over the eleven climbs. The result is expected to be power levels that don’t cause catastrophic equipment failures that can lead to personal injuries or property damage.

The FAI is also considering allowing LiPoly batteries. In the Fall of 2006, LiPoly battery cells started hitting the market with incredibly low internal resistance – the 5000 mAh, 50C, 250 amp types. Low internal resistance means voltage stays high under 50C loads and less internal heat is generated. These batteries will deliver high amps without overheating, weigh half as much as the 16 cell NiMH packs and deliver better climb rates because of the weight reductions.

At about the same time, motors have been coming out, specifically design for this event, that don’t even reach their peak efficiency of 94% until they are pulling 190 amps! Their efficiency doesn’t drop off much even at 250 amps. The challenge is to prop the motor to keep below the 60,000 rpm limit and keep the current in the 200 to 250 amp range, otherwise you’re not making the best use of the motor.
Speed controller development hasn’t been standing still either. Castle Creations offered an ‘experimental’ 300A ESC in January 07 and were sold out in days.

Combine these developments and we will be looking at planes flying at 700 watts per pound this summer. They will climb at 11,000 feet per minute, have almost 5:1 thrust-to-weight ratios and reach 150-mph motor-on velocities then gently land at slow speeds. Motors & batteries won’t be dangerously hot and participants & spectators alike will be safer. Welcome to the new world of extreme electric flight.

Mike Anderson 01-18-2008 02:46 AM

Watts/Lb in real life
 
Just for fun . . .

A Spitfire with a 1096 kW Merlin weighing about 6750 lb flew on . . . . 162 W/Lb.

An Me109 was pretty much the same.

A Zero was closer to 145 W/Lb.

peterboshoff 01-22-2008 05:29 PM

I am starting the other way round.
I have an EMAX 4030-10 brushless motor (5000gm thrust) with an ELF HOBBY 100A Brushless controller and a 5000 mAh 5 cell Lipo battery - but it don't want to work - Can't get the motor powered up - or the ESC programmed - Get "music" but nothing else - other servos connected with the receiver does not work either - Same receiver on another ESC and another motor does work - Does some ESC's only work with certain brushless motors?? IF I can get this monster working I will decide what plane to design. (Close to quarter scale, I presume - once I have learned to fly, though.)

Mike Anderson 01-23-2008 11:30 AM

Debugging
 

Originally Posted by peterboshoff (Post 342513)
I have an EMAX 4030-10 brushless motor . . . Can't get the motor powered up

Assuming this ESC has a BEC, can you operate the Rx on battery power & disable the BEC to see is the BEC is the problem?

On a typical large-scale plane like you're describing, you would not be using the ESC's BEC anyway - that would be too unreliable, unwise & unsafe. . . . once you learn to fly that is . . . probably not in the first year as a new pilot.

gfdengine204 03-28-2008 08:13 PM

I'm getting it, but.....still not quite there yet.
 
I've read this thread a few times, and I think I am starting to understand better. However, I'm curious about one thing: kV. I get the watts per pound, and volts X amps to get the watts, but how do I know what kV motor to use for a particular plane? Or, does the kV follow along with the watts (meaning, the more watts the motor puts out, the lower the kV)?

For example, say I am building a simple foamie, and I have all the TowerPro motors to choose from at www.headsuprc.com. I can always send Jeff at HeadsUp an email, and say "I have this particular plane, what motor combo do I need?", but I would like to learn to figure it out myself. Hopefully I am making sense here.

It's much simpler when I need a motor conversion (say, to replace a .40 glow engine) and go to a website like HobbyCity that has motors listed as direct replacements, but still, I would like to be able to figure this out on my own.

mred 03-28-2008 10:45 PM

The KV is the RPM the motor wants to turn for each volt applied. So for a 1000KV motor it will turn 1000rpm with 1 volt or 10,000rpm with 10 volts applied. The higher the KV rating, the faster it will turn and the smaller prop it wants for it to stay in the Max amp range of the motor. The lower the KV rating, the slower it will turn and the bigger prop it can turn. So if you want a fast plane go for a high KV motor and if you want a big prop with a lot of pull, go for a lower KV rating. For something like a powered glider or 3D type plane you want a big prop for thrust to help it climb or hover, but if you want a fast plane then you will get fast flat line speed, but nowhere near the clime thrust of the bigger props. Hope this helps a little.
Ed

gfdengine204 03-28-2008 10:56 PM


Originally Posted by mred (Post 384097)
The KV is the RPM the motor wants to turn for each volt applied. So for a 1000KV motor it will turn 1000rpm with 1 volt or 10,000rpm with 10 volts applied. The higher the KV rating, the faster it will turn and the smaller prop it wants for it to stay in the Max amp range of the motor. The lower the KV rating, the slower it will turn and the bigger prop it can turn. So if you want a fast plane go for a high KV motor and if you want a big prop with a lot of pull, go for a lower KV rating. For something like a powered glider or 3D type plane you want a big prop for thrust to help it climb or hover, but if you want a fast plane then you will get fast flat line speed, but nowhere near the clime thrust of the bigger props. Hope this helps a little.
Ed

Thanks mred,

I get that the kV equals the RPM per volt; that's the easy part. I guess what I don't get is how to select the right kV value for the plane I want. So if I have, for example, 4 motors that fall in the Watt value I have determined for that particular weight plane, I select the higher value kV if I want more speed, and the lower if I want more thrust?

Also, does the amount of thrust ever come into play here? When I look at the HeadsUpRC pages, it groups the motors by thrust levels, not by Watts.
I really hope I am not making this more difficult than it need be; I'm just having a tough time wrapping my head around it.

mred 03-28-2008 11:17 PM

OK, take two motors that are the same exact spec, except for the KV rating. The low KV motor will turn a bigger prop for things like 3D where you have slow speed , but require a lot of thrust. The lower KV motor would be the choice for this type of flying because it can turn a big prop slow and gives lots a hovering ability. The higher KV motor would still fly a 3D plane, but you would need to use more throttle to hover and would not pull out as fast or not at all.

Now go to a sport plane that is used mostly for sport flying and some stunt playing around and you want a faster, higher pitch prop for speed. This is the high KV motor. You can fly something like a Super Stick on this type of motor because you are not really going to be flying 3D type stuff and you are not worried about hovering with it.

So, if you want high thrust 3D type flying, go low KV. If you want sport fast flying, go high KV motor.

Also, the bigger the motor the slower the KV will be. When I say big, I mean size of motor, not watts. A big motor has more mass to turn, so it has to turn slower where a small motor has less mass, so it can turn faster.

Does this make any sence to you ????
Ed


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