How do I calculate size of motor+esc+battery - RC Groups
Sep 28, 2010, 04:29 PM
busy bee
Question

# How do I calculate size of motor+esc+battery

I am new to RC flying, and have had a few lessons with IC engines, but really want to fly electric.
I have a few models ready to fly, but have recently bought a couple of half built models, both are Black Horse models, one a Piper Cub 72" wingspan, and the other is a Chipmunk with a 64" wingspan.
Both of these are supposed to have IC engines, and I want to finish both & fit electric motors. Can anybody explain how to work out the size motor I am going to need, how to work out the best size of ESC and battery? Is there a formula to work it out
 Sep 28, 2010, 04:44 PM Time for me to Fly... The quick way is to look at a similar size and type of electric plane and copy that power system.
Sep 28, 2010, 07:10 PM
Registered User

# check here

 Sep 28, 2010, 07:22 PM Just having fun +1 on what D B said above. The tutorial he points to is outstanding. Another option in going from gas to electric is the Grayson Hobby EZ-Glow to Electric line of combos. Freddy
 Sep 29, 2010, 04:56 AM Registered User There's a whole forum dedicated to Glow to Electric conversions https://www.rcgroups.com/glow-to-ele...nversions-247/ Plenty of good ideas in there. And depending on which bit of Staffs you're in your local shop might be useful. The Hills at http://www.allelectricrc.co.uk/ have plenty of experience with largish electric models and are very helpful. Steve
 Sep 29, 2010, 06:09 AM busy bee Thanks for all the replies, I did find noflyzone's blog last night, and spent the rest of the evening reading and working out the stall speed of my chipmunk, and looking at the webocalc site. Still not sure what I'm doing though. Will talk with my local shop, and the people at the flying club are very helpful too, I think the more people I talk to, the more I will understand.
 Sep 30, 2010, 12:30 PM Registered User Busy Bee, Find the total weight of the Chipmunk, which may be mentioned at web sites that sell them. You'll need over this much thrust, to fly it straight up. Go to a motor calculator (such as at DiversityModels on the web), and try out different motor/battery/prop combinations, to get an idea of what size motor and prop and battery voltage you will need to get that amount of thrust. Try a range of motor/prop/battery combinations that put out the needed thrust, and look at the ones that give you the longest flight times. Save the continous amps that each combination draws. You will need a speed controller that is rated at maybe 30% more than this continual amp draw. Price speed controllers. Price the motors, and eliminate anything beyond your budget. Look at prop length of each combination: eliminate the ones that will not fit on the Chipmunk. (Look at ground clearance on the Chipmunk.) Find the weight of the best combinations, by searching web sites that sell those batteries and motors. Make sure that the weight is acceptable. Example: if the plane is 7 lbs, you need maybe 120 oz of thrust, or about 80watts x 7lb = 560 watts to the prop. Some options to try on the calculator are: Scorpion 3020/14 600 watts to prop, 46A, 3-5 cell LiPo \$70.00 Monster Power 32 615 watts 58A 4 cell LiPo 12x8 prop 115 oz thrust \$35.00 46 692 watts 41A 6 cell LiPo 10x8 prop 122 oz thrust \$40.00 60 646 watts 38A 6 cell LiPo 14x10 prop 141 oz thrust \$45.00 You'll probably need 4000-5000 mAh of battery power for decent flight times. Try pricing the batteries at hobbypartz.com, and the speed controllers (60-80A). Turnigy plush 80A at HobbyKing are about \$40.00, but may take a month to be delivered. Good luck.
 Oct 04, 2010, 05:00 PM busy bee You have been very helpful, the model is moving on nicely now. Time will tell whether it flies well - or not!
 Oct 04, 2010, 09:42 PM Balsa to the Wall Here's a quick guide from Horizon Hobby: Determine a Model’s Power Requirements: 1. Power can be measured in watts. For example: 1 horsepower = 746 watts 2. You determine watts by multiplying ‘volts’ times ‘amps’. Example: 10 volts x 10 amps = 100 watts Volts x Amps = Watts 3. You can determine the power requirements of a model based on the ‘Input Watts Per Pound’ guidelines found below, using the flying weight of the model (with battery): • 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 NOTE: These guidelines were developed based upon the typical parameters of our E-flite motors. These guidelines may vary depending on other motors and factors such as efficiency and prop size.