RC Power FAQ

1) Beginner issues

A101	Why fly electric?
A102	How do I get started?
A103	What kind of planes can I fly with electric power?
A104	How do I sign up for the AMA/MAAC?
A105	What Kind of equipment do I need?
A106	What special tools would I need?
A107	Can you suggest a few beginner setups?
A108	Are soldered or crimp joints better?
A109	What goes on which stick?

2) Safety

A201	What safety procedures should I follow when flying?
A202	What is an arming switch?
A203	When should I use an arming switch?
A204	How much power will I lose? How much weight will I gain?
A205	What is a fuse? Why use one?
A206	What type of fuse should I use?
A207	How do I choose the fuse rating?
A208	How and where do I install the fuse?
A209	Are there any safety precautions for the motor battery?
A210	How do I fuse a brushless motor?

3) Batteries

A300	Battery Basics
A301	What's Volt, Amps, "C" rating, etc....?
A302	What are milli-amp hours?
A303	How fast can I charge my batteries?
A304	What is Nicad memory?
A305	What is Cell reversal?
A306	Should I cycle my packs?
A307	Can I deep discharge an individual cell safely?
A308	What is the discharge of a Nicad like?
A309	Black Wire Syndrome
A310	Low Tech Cell Matching
A311	What are the effects of series and parallel?
A312	What are NiMH batteries like?
A313	Can I use Lithium batteries for electric flight?
A314	What do the battery codes like SCR, AE mean?
A315	Is it safe to solder directly to batteries?

4) Electric motors

A401	What does "breaking-in" a motor actually do?
A402	How do I break-in a motor?
A403	What does gearing do?
A404	How do I compare an electric motor to an IC engine?
A405	What are motor constants?
A406	What's the difference between Delta and Wye Brushless Motors?
A407	What is "timing"?
A408	How much should I advance a speed 400?
A409	How do I use the "speed 400 timing tool?"
A410	How much heat can our motors dissipate?
A411	How can I keep my motors clean?
A412	What is a sensorless motor/controller?
A413	How does a sensorless motor work?
A414	What do the motor names (Speed 400,600, 05, 25) mean?
A415	How do I do a "Water break-in" ?
A416	How do I measure motor constants ?
A417	Will this cheap Mabuchi 540/380 etc. be good for E-Flight ?
A418	How many capacitors do I need on my motor and what values ?
A419	Should I wire two motors in series or parallel?
A420	Where can I find some information on common brushed motor constants?

5) Speed controllers (ESC's)

A501	How does a speed control work?
A502	What is the advantage of a High Rate Control?
A503	What is the best switching rate for a hi rate ESC?
A504	How does a motor brake work?
A505	What is a BEC and how does it relate to the speed control?
A506	What are the disadvantages of a BEC?
A507	What is a Cutoff?
A508	How long can I fly once the cutoff takes place?
A509	What is opto-isolation and what does it do?
A510	How do I disable the BEC on my speed control?
A511	Where does my BEC speed control plug in ?
A512	Can I control 2 brushless motors with one controller ?

6) Propellers

A601	Why doesn't my Graupner folding prop extend all the way out?

7) Chargers

A701	How does charging current relate to capacity?
A702	How can I make certain my packs are fully charged?
A703	How does a peak (or delta peak) charger work?
A704	Will my charger work with Ni-MH batteries?
A705	Will a NiCad peak charger work with Lithium batteries?

8) Model info

A801	What are the differences between Indoor, Slow and Park flyers?
A802	What are EDF models?
A803	What exactly are EPS/EPP/Depron and other construction foams ?
A804	What is the watts/pound rule?
A805	What does the Watt-hours/pound rule tell me?
A806	How do I match an electric power system to a given airframe?
A807	How do I convert a gas powered plane to electric?
A808	Are there any proven electric setups listed anywhere?

9) Electrical formulas

A901	How do I calculate duration?
A902	How do I calculate Watts?
A903	How do I convert units of measure?
A904	What is Orme's Law?

Reference resources
Mailing lists
FTP sites
Web pages
Newsgroups
Non-electronic Resources
Magazines
Books

Contributor Credits

I'm building an electric twin. Should I wire my motors in series or parallel?

Q. I'm building an electric twin. Should I wire my motors in series or parallel?
A. Doug Ingraham

There are several reasons why series connections are better than parallel but the biggest reason is efficiency. If you hook the motors in series the no-load current of both motors together is equal to the no-load current of the individual motors so you don't suffer in that area. The rm is twice as much but this doesn't matter since the voltage is doubled, and the current is the same as a single motor so the losses in series are the same as for single motor systems. If you parallel the motors the no-load current is doubled and in fact all currents are doubled. This is very bad because losses are based on the square of the current.

If your system resistance (batteries+esc+wiring) is 0.045 ohms and you draw 30 amps from a single motor with the losses in the system are going to be (i^2)*r=40.5 watts with a single motor or with motors in series. In parallel the current will be 60 amps so the losses will be 162 watts for all losses up to the motors. As for failure modes, in parallel if a motor shorts both motors stop. If a motor opens one motor stops and the other continues normally. In series if a motor opens up both motors stop. If one motor shorts the other motor will try to go twice as fast (throttle back quick).

In parallel you need a controller that can handle twice the current. The batteries will go dead twice as fast so your duration will be half. In series you need twice as many cells so the weight is going to go up. You need a speed control that will handle the extra voltage. You also will need a charger that can charge twice as many cells. Usually the extra cells won't matter in a twin setup because you are doubling the power. Cutting the duration in half usually makes people unhappy. So why does anyone use parallel? because with speed 400 size you can get away with it and it doesn't kill you. 20 amps is no big deal from 1700scrc cells and speed controllers are common that can handle this. Expect to have excessive losses with any motor setups larger than these.