Getting Started In Electric Flying (ERCITS)
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NOVEMBER, 2002 Newsletter

Past Newsletters

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NOVEMBER Articles

Convair 580

Field Box

How To Be Successful Building & Flying Electric Powered RC Planes

OV-10 Bronco

Partenavia

Retracts

Twinstar


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Getting Started In Electric Flying

By Peter Dennis - Flying Sites Editor

Electric flying is something I've just got into myself! I have been flying over 21 years but wanted to try this side of the hobby. I do not profess to know the ins and out and all the technical details of watts, amps, milliamps, brushless motors or the number of turns required to make a hot motor. But outlined below are some of the basic things I have learnt while getting into the electric side of our hobby. I hope it will help you understand some of the basic concepts.

Indoors Or Out?

Deciding what to buy all depends on what you want to fly. Outdoors or indoors? Indoor models, although smaller and less expensive tend to be a little more difficult to fly if you are a novice. This is because of the confined spaces in which most indoor models are flown. The walls always seem to close in on you after you take off! Most people probably start with an outdoor model. One of the most popular models currently is the Multiplex Twinstar, or if you want something that's a bit more responsive the Multiplex Twin Jet is also very popular. Although I have started with the Kavan Partenavia (see review on this site).

All these models are made of expanded polystyrene foam. This gives them a very light structure and cuts down on building time. The standard electric motor is the Speed 400 or Speed 480. These are usually used without gearboxes (direct drive) in the above examples. They use plastic 'Gunther' props (usually supplied) which just push on to the motor shaft or a props around the 6x4 size, which will require a small prop adapter.

Speed Controllers

Models of this size can use standard radio gear but sometimes people will use smaller servos to save weight. A speed controller is in fact your throttle control. These are sometimes called ESC's - Electronic Speed Controllers, The ESC is small electrical devices that, at one side plug into your power pack battery and out of the other side to your motor(s). They also contain a servo lead that plugs into the socket on the receiver usually used for the throttle. This eliminates the need for a throttle servo, as the speed of the motors is controlled through the ESC. Some ESC's also have a seperate 'arming' switch.

Most ESC's have what is called a Battery Eliminating Circuit (BEC) this means that all your on board radio gear (rx, servos) are powered from just the one motor power pack, thus eliminating the need for a separate battery to power your radio gear. When the power pack discharges to a fixed voltage during flight, the BEC will automatically cut the power to the motor(s) at that point, but continue to supply the receiver. This allows you to land safely with out loss of radio communications.

ESC's are rated at different ampreages, from around 2 amps to 50 amps. You choose the one to suit your power pack and motors. In the above examples the Twin Star usually uses a 7 or 8 cell pack (8.4v - 9.6v), which will draw around 20 to 30 amps. In this case an ESC rated at 35 amps would suffice.

Battery Power Packs & Charging

Battery packs come in a variety of sizes and number of cells. Each cell has a voltage of 1.2v. But cells are also rated by the amount of charge they can hold. This again is rated in amps or milliamp hours. So if you see a pack marked 8 cell 2000mAh, then it will have a voltage of 9.6v (1.2 x 8) and will be able to hold a current of 2 amps (2000mAH). A constant current of 2000 milliamps would take 1 hour to discharge the pack. Of course our models draw a lot larger current than this during a flight and the pack discharges more quickly. In around 6 to 8 minutes usually.

Conversely, a 2000 mAh pack can be charged in 1 hour if supplied with 2 amps! There are many fast chargers on the market. All have their pros and cons. I use the Super Nova 250s. At around 70 it has features that more expensive charger don't have. It will charge and discharge your power packs automatically, both NiCad and Nickel Metal Hydride (NimH). But you can also set in your own rates manually as well if you wish. It can also charge your 12v field battery (Pb - plasma battery). One disadvantage of the Super Nova is that it runs from a 12v supply. Great at the flying field where you just plug onto your car battery, but not so good at home if you want plug into the mains! However, transformers are available. (You will need between 9 and 15 v constant supply at 5 amps for the Super Nova. Maplins produce such a transformer for around 45). In my experience the Super Nova will charge a 2000mAh pack in around half an hour.

One final point about batteries. A new pack must always be given a slow charge for the packs first charge. This conditions the pack for fast charging by giving the pack its full capacity. If you were to give it a fast charge to start, the pack may never again reach its full capacity, thus giving you less running time. A slow charge is usually at a 1/10th (or C/10) of the pack's capacity. 200mAh for 10 hours in our example. Although in reality this is usually about 12 -14 hours.

Reprinted courtesy of Flying Sites

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Updated November 14, 2002.

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