Hello everyone.
I build scratch planes. This winter I plan to build a foam Polikarpov Rata and a bunch of the swapables though probably without swapping pods. After flying for years and buying motors and esc on recipes online I am looking for some fairly easy way to choose the entire righ. I would really really really like some step by step advice.
Thanks in advance.
I have two examples of planes for which I need engines:
This is a foam version of the GP Slowpoke. It is now running on a RC A2212 2200KV Outrunner Brushlessmotoren w/30A Regler. The prop is a foldable 7.5/4 and it usually runs on a 1250 11.1v.
I am not very happy with the performance of this plane. I flies well but if has no pop and it sounds like a fly. I have at least 4 or five other planes that need to be rerigged.
This is a small foam j3 typeathing. It is basically finished. It has a 1m wingspan.
Log In to reply
Log In to reply
http://www.ecalc.ch/motorcalc.htm?ecalc&lang=en
If eCalc is all gibberish to you, then go to this article about picking props/motors.
http://oddcopter.com/2012/02/06/choosing-quadcopter-motors-and-props/
It's geared towards quads, but down lower on the page is a series of links for "understanding the science" and the articles it links to cover all the things you'll probably want to know about motor construction and ratings to set you on the right track and how to better use eCalc.
Log In to reply
Log In to reply
50-75 Watt/lb - glider or trainer
100 Watt/lb - aerobatic
150-200 Watt/lb - 3D
Calculate your total weight (battery and motor included), and figure what type of plane you want, then determine your watts. Remember, you can always throttle back, but you cannot make a weak motor give more power (when in doubt, use more power and deal with the weight).
Log In to reply
50-70 watts/pound: 11-15 watts/100g Minimum level of power for decent performance
70-90 watts/pound; 15-20 watts/100g Trainer and slow flying scale models
90-110 watts/pound: 20-24 watts/100g sport aerobatic and fast flying scale models
110-130 watts/pound: 24-29 watts/100g Advanced aerobatic and high-speed models
130-150 watts/pound: 29-33 watts/100g Lightly loaded 3D models and ducted fans
150-200+ watts/pound: 33-44 watts/100g Unlimited performance 3D models
Log In to reply
• 50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
• 70-90 watts per pound; Trainer and slow flying scale models
• 90-110 watts per pound; Sport aerobatic and fast flying scale models
• 110-130 watts per pound; Advanced aerobatic and high-speed models
• 130-150 watts per pound; Lightly loaded 3D models and ducted fans
• 150-200+ watts per pound; Unlimited performance 3D models
Step #2: Divide the total desired watts by battery voltage to determine necessary amps.
Watts / Voltage = Amps
Step 3: Determine the Voltage to /Currant ratio by dividing the given Amp by the Voltage.
Amps / Voltage = V/C Ratio
Voltage/Currant ratios should be fairly low; 2 or 3 to 1 being ideal.
Examples: 900w / 11.1v = 81a 7:1 ratio
900w / 14.8v = 60a 4:1 ratio
900w / 18.5v = 48a 3:1 ratio
900w / 22.2v = 40a 2:1 ratio
Step 4: Determine the battery discharge rate (C-rating) by divide the desired Amps by the battery pack capacity, expressed in Amps (A).
Required amps / Capacity (A) = C-discharge rate
Example: 40amps / 4 (4,000mAh) = 10C
Step 5: Determine the Max. full throttle flying time, full discharged battery time by dividing 60
minutes by the C-rating.
60min / C-discharge rate = Max. full power time
Example: 60min / 10C = 6 minutes
Step 6: Determine the 80% discharge flying time by multiplying the Max time by 0.8.
Example: 6 minutes x 0.8 = 4.8 minutes.
Clear as mud?
Log In to reply
Log In to reply
The math, and path through it is good. A lot of guys will argue that you NEED to start with the proper size prop, but that's easily taken into consideration once you runt the numbers and actually start looking for specific motors.
I have a worksheet in Excel that does all the calculations automatically, and allows you to try different options to compare and find an efficient system I make the worksheet available through email, just send a message (redbaronrc@gmail.com) asking for the e-power worksheet.
Log In to reply
Log In to reply
http://flbeagle.rchomepage.com/software/webocalc_1.7.6/webocalc.html
Log In to reply