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Electric flying

I tried to fly an electric model a few years back. It was an RCME Hushabye design (RM165). It didn't fly but it wasn't the fault of the design. The motor, RC and cells that I was using were just too heavy and the throttle was a simple on-off microswitch triggered by a servo. At the time I gave up.

When I visited a club field a little while ago I was surprised to see an electric model flying at speed and doing aerobatics. I decided to look into it. I was astonished at the improvements in motors, batteries and controllers.

Brushless motors

The compactness, rotational speed and power of brushless motors is impressive. It took me a while to realise that they were small three-phase motors. I was puzzled where the driving waves came from so looked into electronic speed controllers. Not only do these produce the three phases at very large currents but they can be programmed for braking the motor, throttle response and other things. You can even change the sounds they make. My favourite ESCs are Turnigy Plush. They are quite cheap, compact and very robust and they can be programmed using a cheap card rather than struggling with beeps from a transmitter. To read more about how brushless motors and ESCs work click here.

For help with choosing the correct size of motor click here.

Lithium-polymer (lipo) batteries

Lithium-polymer batteries are also impressive. Unless you are planning to boil a kettle, shorting them is a bad idea as I discovered. Luckily a window was nearby. That, and avoiding a full discharge, are the only vices. Otherwise they pack a huge amount of energy into a compact and light package.

Graphene is now being used in Lipo batteries so I bought some. They seem to run cooler, probably due to lower internal resistance. It is said that they can be recharged many more times than conventional ones. I don't yet know for sure but, after nearly two years of use, several standard lipos have started to swell and lose peak power but, in identical models, none of the graphenes have. Worth the extra I think. Even better I have measured the internal resistance of the new Turnigy Panther graphene batteries and found that it is about half that of the black graphenes.

I am careful not to discharge lipos fully. However I left a battery in a glider with the receiver switched on. When I realised it, the battery was down to 0%. I was tempted just to throw it away but it was a graphene and I decided to try a recharge. To my surprise it charged without complaint and appeared to be back to normal performance. Time will tell, but it looks as though graphenes are more resistant to full discharge.

The energy cost is low - about 5p to charge a 3S 2.2 Ah - but there is one major drawback with electric flying. With IC flying you use the same fuel in all of your models. Apart from the 2.2Ah 3S size which is used for many small and medium sized models, you have to buy a whole range of different sizes of battery. It gets expensive.

Connectors

For a picture guide to power connectors click here

Electrical theory for modellers

If you are uncertain about electrical words like voltage, current and resistance click here

My favourite charger

I now use an iSDT SC-620 500W battery charger. This has many functions including displaying the voltages and internal resistances of each cell. It can supply 20A from a suitable 12V supply like a leisure battery. For a video review try: https://www.youtube.com/watch?v=lJX8s8pxgqI

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(C) Peter Scott 2015

Last edit 10 October 2018