Hello!

I recently built a Great Planes PT Electric trainer for my little brother as his first plane.It comes with a direct drive 550 brushed motor, and a switch harness in place of the ESC. What sized brushless, outrunner motor, ESC, and battery would fit this plane?

I have no clue as to how electric motor sizes, batteries, etc would fit a model, and want to keep it cheap.
Leadershobby has some nice looking equiptment for sale at really low prices, but I'm not sure what is good for this size model.

56 in WS
3 lb AUW

Thank you,

Graeme

It is always best to provide a link to the plane you are asking about.   Is this your plane?
http://www.electrifly.com/largeelectrics/gpma0110.html 


In any case, there is a good book at the top of this forum that is all about electric flight.  You may wish to take a look.

But, assuming your plane is 3 pounds with the stock motor and the recommended battery, then we will use that as our weight target.  A new outrunner brushelss motor and Lipo battery may be able to shave a few ounces off that number.

Your target power to weight ratio should probably be between 60 and 100 watts/pound.  I will use 75 as the target since this is a trainer.  So you are looking for something in the 220 to 250 watt range.  Assuming a 3 cell lipo, at 11 volts, that would suggest a motor/prop combination that will draw in the 20 to 23 amp range. 

A 1000 kV brushless outrunner with a 10X7 prop would be a good starting point.  Or a 1200 kV with a 9X6 would work too.

A 2400 to 3600 mah 15C or higher rated 3 cell lipo pack would probably be a good target.

Naturally you can go more powerful, but I would not recommend going less.

Thank you for the data!

Yes, the model stated is the one - I'll see what motor/ ESC combos are in my price range.
I was also interested in having a power combination that can be transfered to a future model.

Thanks again.

Graeme

Is this motor any good? I know it is slightly above you're specs, but it's cheap...

http://leadershobby.com/product.asp?ID=9394001110012

<div class="shape" style="PADDING-BOTTOM: 2.88pt; PADDING-LEFT: 2.88pt; PADDING-RIGHT: 2.88pt; PADDING-TOP: 2.88pt">Actually it is somewhat below my specs.  kV is right but the amp levels are a bit low.  <span lang="en-US">Continous current is 18A  I was targeting 20 - 23.   Max of 22A is usually a 15 second number so you better not leave that throttle open.

It says max power of 360W but I think that is a mistake.   11V X22 Amps ( max) = 242 Watts.  11X18 = 198 watts.   Assuming they are not out and out liers, that has to be a typo.    And a claim of 98% efficency seems VERY optimistic.  Something in the low 80s is more likely.

Note also that props are smaller than what I recommend.  ( 8" x 5"/ 8" x 7"/ 9" x 5")  although 9X5 is close to 9X6.  I modeled a 1200kV motor with a 9X6 at 22 amps, so this one with a 9X5 is probably right at 18 amps.

This one is OK, but the a little on the light side for my tastes.  I think performance would be a bit weak.  I would not choose this one.  
 
</span>
<p class="MsoNormal"><span lang="en-US">
Rotational Speed      1200 (kv) RPM/V</span></p><p class="MsoNormal"><span lang="en-US">Continuous Current  18A</span></p><p class="MsoNormal"><span lang="en-US">Max. Current    22A</span></p><p class="MsoNormal"><span lang="en-US">Input Voltage   6 - 11.1V</span></p><p class="MsoNormal"><span lang="en-US">Max. Efficiency       98%</span></p><p class="MsoNormal"><span lang="en-US">No Load Current      0.8A</span></p><p class="MsoNormal"><span lang="en-US">Internal Resistance         98mΩ</span></p><p class="MsoNormal"><span lang="en-US">Power       360W</span></p><p class="MsoNormal"><span lang="en-US">Motor Weight (Motor only)         60g</span></p><p class="MsoNormal"><span lang="en-US">Motor Dimensions (Diameter x Length)         28mm x 27.3mm</span></p><p class="MsoNormal"><span lang="en-US">Propeller Dimensions 8" x 5"/ 8" x 7"/ 9" x 5"</span></p><p class="MsoNormal"><span lang="en-US">Input Battery Types NiCd/ Nimh/ Li-po Battery</span></p><p class="MsoNormal"><span lang="en-US">Recommend Model Airplane</span></p></div>

Thanks again - this is why I like RCuniverse!

What sizr of battery would work with this model?

<div id="TixyyLink" style="BORDER-BOTTOM: medium none; TEXT-ALIGN: left; BORDER-LEFT: medium none; BACKGROUND-COLOR: transparent; COLOR: #000000; OVERFLOW: hidden; BORDER-TOP: medium none; BORDER-RIGHT: medium none; TEXT-DECORATION: none">A 2400 to 3600 mah 15C or higher rated 3 cell lipo pack would probably be a good target.


</div>

Thanks again!

Are there any basic charges available for LiPo's? All the one's I keep seeing have lots of features, screens, etc, and seeing that I will only be using it on this model, I don't want to invest in an expensive one.

  - Lots more to electric than I thought!

Thank you,

Graeme

I have the CellPro 4. Super easy and super reliable. It is the one I recommend. May be more than you want but I won't recommend less. Does all chemistries.

http://www.fmadirect.com/detail.htm?item=2306&sect;ion=45

High Quality 2 cell
http://www.fmadirect.com/Detail.htm?...amp;section=69

High Quality 3 cell
http://www.fmadirect.com/Detail.htm?...amp;section=69

Sounds good to me!

Thank you for all the help regarding my model - I wouldn't have had a clue otherwise!

Graeme

This balancing charger would be fine: http://www.okhobby.com/product.php?id_product=1075 (I reviewed the 50W version and found it to be good for basic needs)

Hi,
I am in the  process of scratch building a small Shoestring Racer. I want to power it electrically but, I have a very limited knowledge if electric power. My question is this; With a 30 inch wingspan amd not weighing over 20 ounces, How do I determine what motor size and battery size should be run in it?
Thanks
Wyattjr