Hello

First of all, I know nothing about RC systems so if you are able to help me please assume zero knowledge.

I've just purchased a Futaba 6EX 2.4GHz system, in the box are four servos fitted with discs.  Also in the box is a packet containing all the fixings together with servo arms; 4 of them have 6 arms and one has 4 arms.

Which do I use in my plane?  The diagram in the Futab instruction book shows servos with 4 arms but only one is supplied!

 The instructions for my Great Planes Piper J-3 Cub says I should cut all the arms off except one!

 What is the correct way to set-up the servos?  Do I use the discs with no arms?  Servos with 6 arms?  Servos with 4 arms or as the Plane instructions say, a servo with only 1 arm?

Please help de-mistfy this for me. 

Hiya Alan

the servo arms can be easily removed and swapped around with a few twiddles of a screwdriver.

It's common practice to chop an arm or arms off servo discs so that the servos will fit in the model without the output arms fouling the sides of the fuselage or the arms of other servos.

The different holes in the servo arms give different amounts of lateral (push pull) movement through the pushrods for the same rotational movement of the servo. This can also be achieved through the rates switches, and end-point settings on your TX (if available), although once these are at maximum/mimimum, the only way to further increase/reduce movement is to adjust the linkages

The circular disks are handy if you want to drill a hole in between two existing holes (for a very precise degree of movement), or if you want to create a cam, e.g. to push against a button on a camera for in-flight photography, in which case you carve the disk to the requisite shape, and mount the servo so that the disk is straight above the shutter release (Shutter release! I'm really showing my age).

NBs

 - Servos buzzing when the control stick is stationery (in whatever position it's in) means a binding control, higher current draw, and potentially failure - sort it!

 - Clevises will foul the other arms of the servo disk, and the mounting spigot unless these are cut away or the clevis is positioned far enough out from the central spigot.

 - A Z-bend in the end of a control rod, if accurately made, is effective and lightweight. An alternative in installations where access is limited is a single 90 degree bend and swing-keeper

 - Loose mechanical connections between snake/pushrod and servo will result in imprecise flight characteristics.

 -  Your transmitter functions can probably be made to counter the effects of sloppy servo installation, but should really be used to fine tune a good servo installation.

 - Not all servo disks are the same - use the same brand of servo arms as that of the servo, or things can go pear-shaped.

 - Servo disks can make useful throttle arm replacements

Many thanks Alistair, the fog is lifting

He he!! Use whichever arms/disks suit your installation! Most peope use the arms, The disks work better with the type of pushrod connector that bolts through the disk, and then the rod goes through a little hole and is then clamped by a screw, similarly to the wires in mains plug! Regarding cutting the arms off, you only need to do this if space prevents the mounting of servos side by side without the arms on adjacent servos clashing, or if the control rod run is such that at full deflection, an arm clashes with the control rod. (ie in fully pulled position, the next arm in the circumference catches on the rod. If you need more arm outputs than you have, they are available as spares, or you can cut a 'V' notch close to one of the lines of holes in one of the disks to give clearance.

With the servos installed, everything plugged in, and the trim buttons adjusted so that they are in the centre, put the arms onto the servos so that they are at 90' to the length of the fuselage (in case you have put the servos in across the fuz, as some installations call for), so that they have equal movement fore and aft when you move the tranny sticks.

The important thing to remember is - when plugging the power and servos into the receiver, with the socket end to the right, the black wire in the plugs (-) goes to the right, (outside) end, and the signal wire, (yellow, pink, whatever) goes to the inside. The middle pin is the red (+) wire. So when plugging in the power wire, with only two wires, the unused one is to the inside.

When you connect the switch, if you use it, there are three connectors, one socket for the charger and two plugs, one red, one black. If you look on the plastic trim for the switch, it is marked on/off. In the off position, the battery can be charged without unplugging anything else, via the black plug. The red one goes to the receiver. If you have things set up like this, and nothing at all happens when you have the switch in the on position, but the servos work when supposedly off, swap the two plugs around!

Edited - Alistair beat me to it while I was typing a response 

Eric, another very helpful response.  Thanks

Hi Eric, its a Beagle but a bit squahed in the photo