Radio Installations - Part 2 (Receivers And Battery Packs)

Recievers for model aircraft have come on in leaps and bounds over the last few years in both size and reliability. The main reason for this is the advent of smaller battery packs becoming available at very reasonable prices. This in turn has lead to smaller models such as indoor and park fly models, where not only is there a requirement for reciever batteries but also motor power is taken from the onboard pack.

Here is a standard 7 channel reciever

And this tiny object wrapped in foam padding is a more modern reciever. (little more than a circuit board).

The best place to mount your reciever in your model is usually dependant on the type and size of your model. Its is best placed in an area large enough to house both the receiver and enough protective foam to save it from damage in the event of a crash or hard landing (or arrival as it is sometimes known).
Another point to take into account is will the servo leads reach whilst still slack and not interfering with servo arms.

An overstretched servo lead can fail and usually does when you're trying to perfect that impressive new manouver. A little forethought will save you a lot of heartache. Seen here on the right is a handy little gadget if used correctly, Its a failsafe device that will take over certain functions on your model in the unlikely event of radio failiure. At about £13.00 this device will close the throttle ensuring that your model does not come down like a cruise missile at 200mph when a radio suffers interference. On a modern computer radio set the failsafe is normally built in to the system. The difference between the two is that on the computer set all main functions are catered for. So that in times of trouble the model can be set on a safer course as well as shutting down the throttle.

Failsafe

And that is exactly what the failsafe is for, not as some think to automatically land your model for you but to ensure that your model comes down in a predictable way and anybody in the area can move safely away whilst the model suffers as little damage as possible.

Come in many different shapes and arrangements. So here we are going to look at three common types. The first and most common is the four cell receiver pack.
These days the capacity of a standard sized AA cell can be as much as 1800mah. This is three times the capacity of that when I first started in this hobby. Cells of this size can be very useful when your model has five or more servo's to operate. and will guarantee a full days flying without worry from a fully charged pack. Also If you fly helicopters the strain on your flight pack is greatly increased as servo's tend to be under far greater load and higher performance in terms of speed and power.

Older600mah receiver pack..

1500mah pack the same size..

The next type of pack were going to look at is the 6V pack (five cells). Again used for radio flight packs but usually in large scale models. This configuration started as models began to increase in size most notably with gliders as thier long wings mean that servo lead lenghts are much greater and more current is required to cope with this situation. Most modern recievers/servo's will cope with six volts although it simply is not nescessary with trainer type models and basic sports types.

2000mah 4.8v heli pack..

6v 1700mah home made pack prior to heat shrink application..

All of the above battery packs will usually be located at the front of the model just behind the firewall above or below the fuel tank. The important thing is that as this is the heaviest item it is used to balance the model as near to the correct Centre of gravity as possible.

Last but not by any means least is the ever popular electric flight pack. Consisting normally of seven or more cells these battery packs are used to power both the reciever and the motor of the model. Each supply being seperated by an electronic speed controller which proportionally increases power to the motor as you move the throttle stick on your transmitter whilst giving a constant supply to your reciever.
As there is a very large increase in size and weight of these packs they tend to sit around the center of gravity on most models. This of course changes when install in a pusher type model as with the increased weight of the motor at the back you must move the battery forwards to counteract this effect.

Here you can see a classic layout for an electric glider eg. motor speed control and flight pack.

This layout is for a pusher type model. The flight pack is well forwards and further back is the speed control and receiver (being lightest at the back.

Well thats about all for this section on radio installations. and I welcome your comments. I do hope that this answers most of your questions, however if you would like to know more please feel free to contact me at : webmaster@bumpygreen.co.uk

Article by Grot from Bumpy Green Model Aerodrome
30th September 2001