eCalc Motor and Prop Efficiency Guide

Disclaimer: I have been at the drone business about two months (since Christmas). I have noticed that there is a lack of How-To's, unlike other RC forums. How-To guides are nice when you want to do a simple search and get results with having to weed through pages and pages of discussions. I hope to keep blogging my progress to help other noobs.

Setting up my first drone, I did a search for "motor and prop efficiency" and came up with a couple references to eCalc. It is an online calculator that calculates flight times for all sorts of flying drones. I will use the example of my latest build, a Bixler 1.1. eCalc can be pretty overwhelming at first, but it becomes a breeze with some practice.  Note: eCalc is now commercialized, but there is a free version with limited options, and a one year subscription costs just $5, well worth it.

First, you need to plug in your motor cooling, field elevation, and ambient temperature. Notice that when you put int the ESC, you need to put in the surge or burst rating:

Now, put in your battery information. If you cannot find your particular battery, find a close match in C-rating and capacity and allow the program to populate the rest of the fields for you. Then, go back to the drop down and select CUSTOM. In my example, I chose a 2100 mAh battery, but went back and changed it to 2200 for more precise flight times:

Next, choose your motor, or one from the drop-down that matches pole count and can size (diameter and can length.) Allow the program to populate the rest of the fields for you and then go back and change the fields with information from the manufacturer's website. In my example, I had to change power (watts) and weight:

Next, select a prop and press CALCULATE. You want to experiment with motor and prop combinations that do not give you the red warning letters:

After first writing this post, I encountered a problem. I couldn't find a prop in the size I was looking for! Make sure you can easily acquire the prop you generate results for.

After making some changes, the most efficient prop for this motor is a 6 x 3E from APC. Notice the flight times offer you a range, depending on your flying style:

I just flew this particular combination yesterday, and the "most efficient" isn't always the best. In my case, the plane flew on the cusp of stalling with very little reserve thrust. It would literally stand still in ~20 MPH winds! I changed out for a 6 x 4E prop which gives much more power while sacrificing very little in flight times:

I can attest that the accuracy is dead-on with eCalc. At 10-11 minutes of flight time, my battery is at 50%. I hope this helps someone out on their journey!

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Tags: and, combinations, efficiency, motor, prop

Comment by Gary McCray on March 1, 2014 at 7:46pm

Hi Dave,

This is a very nice write up of using Ecalc to optimize motor / prop / battery selection.

This fixed wing oriented Ecalc example is also very similar to this one for multicopters:

http://www.ecalc.ch/xcoptercalc.htm?ecalc

I think it would probably be useful to convert your page into a wiki page and I am happy to do so if you don't mind.

Best Regards,

Gary

Comment by Gary McCray on March 1, 2014 at 9:53pm

Small glitch with eCalc Link auto page switch, but now fixed.

Your new eCalc wiki page is here,

http://plane.ardupilot.com/wiki/ecalc-motor-and-prop-efficiency-guide/

Please let me know if you would like it edited or anything added to it.

Best Regards,

Gary

Comment by mdisher on March 1, 2014 at 9:56pm

Bummer, I just played with this the other day.

Comment by Gary McCray on March 1, 2014 at 10:11pm

I got it fixed now, you just cant link straight to eCalc destination page.

eCalc does an auto jump through its sign up page and you cant skip it.

Follow the link in the wiki page, it goes there fine now.

There are limitations to the Demo (non-paid) version (less motors and batteries).

Comment by Pedals2Paddles on March 2, 2014 at 12:33pm

I spent many hours on eCalc choosing the components for my UAV that i'm building right now. Whoever is responsible for it is a hero.  I never noticed the demo/paid thing though.  I had always wished I could save my results.  I'll definitely be buying a subscription soon!

Comment by Pedals2Paddles on March 2, 2014 at 12:35pm

I think it is really important to point out though about the power required at hover.  It lights up red at 80%.  This according to my reading is way to high.  It should be more like less than 60% I think

Comment by Peter Seddon on March 3, 2014 at 6:30am

I am concerned about the motor selection for this application - a 1400kv and 6 x 3 prop. Small high revving props are not very efficient and for a 'copter that spends a lot of time in the hover a better solution would be a larger prop (say 10 x 4.5) and lower Kv motor. 

Peter

Comment by Pedals2Paddles on March 3, 2014 at 6:51am

Peter, I think you're confused. The eCalc doesn't choose a motor and prop for you.  Whatever motor and prop is showing up is the motor an prop you choose yourself.  You choose each component yourself.  eCalc then fills in the statistics at the bottom about run time, power, efficiency, etc.

Comment by Dave Smith on March 3, 2014 at 7:52am

Peter, the example that I used is a Bixler 1.1 fixed-wing UAV. There is a different link for multirotors here. You are dead-on about high revs and poor performance. After experimenting more hours than I would like to admit, my next purchase for my Bixler is a 35-25-640kV motor and 8 x 5 prop. With the exact same battery, it changes my flight time from 18 minutes to 38 minutes! Pedals is exactly correct, you need to have a "starting point" and then start throwing in different motors and props and start playing with the results.

Comment by Dave Smith on March 3, 2014 at 7:53am

^^^^^^And, I forgot to add that it increases thrust by 150....

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