Motor Selection

[davidfoley]

Hi Guys,

I have the 36.6in Hobbyking Yak54 (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10350), and I am looking to replace the geared inrunner with an outrunner. I am interested in learning what motor, ESC & prop combination I should use to retain similar performance to the stock setup.

However what I am more interested in is learning some general rules about how this decision should be approached.

1. How can I look at a plane and decide what drive setup I need?
2. What are the key specifications of a motor other than the Kv?
3. How can I match a motor, ESC and prop?

I am not looking for a super accurate answer, some rough guidelines would be great

Many Thanks, Dave

 

[pgerts]

1 - most important is the total weight of the plane.
1b - what type of plane - slowflyer, sport scale, racer, hotliner/pylon
2 - the power of the motor (Watt) comes from the battery (volt) and the motor current (ampere).
2b - the KV comes from the choice of torque (low KV) och speed (high KV).
3 The motor amps determines the selection of ESC (get some margin like 20% higher than max amps for the motor).
3b - The prop is from the combination of motor current and KV (revs). The best is to find tests and read the recommendation of prop size for each battery (number of cells = volt). Next is to measure yourself after reading info on similar motors recommendations.

A Yak is an aerobatic and i would select torque instead of speed.
A motor with 900-1100 KV and a weight of 40-50 grams with a max amp of 20A.
An 25A ESC
A 8*4 up to 9*6 propeller depending on the KV and recommendations from the selected motor.

 

[earthsciteach]

This is the most comprehensive discourse on your question that I've found. I'll call it, "Everything you wanted to know about electric power systems for airplanes plus more information that you want to deal with."
http://www.wattflyer.com/forums/showthread.php?t=18521

 

[davidfoley]

These were very helpful replies, thank you very much

@pgerts: Based on your suggestion do you think either of these motors would be suitable? I saw the second recommended for this place on another forum, would the extra 30g be a big problem?

1) http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11879

2) http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=24537

Many Thanks, Dave

 

[pgerts]

Any of the motors will be fine depending on the type of flying you want.
You can use #1 with a lighter battery like 800-1100 mAh to get a slower flying plane and #2 with a battery slightly bigger round 1500 mAh. Dont get the cheapest battery with low C like 20 but a slightly better battery with a C of 35 or better.

You will get other answers depending on the type of pilot you are asking but some old pilots have told me that every gram you can save will make a plane fly better - and i can only agree.