What is the best method of installing servos to ensure correct servo sense is in operation to avoid the bad practice of reversal by using the Transmitter?

From : Don Stackhouse

Excellent question. Fortunately there is an excellent answer:
Don't wait till the airframe is all finished and closed up to start working out the radio installation.

While there is still one face of the tail cone open (so you can still get at the pushrods), do a "trial fit". In the case of the 2-meter Crysalis, step 6 (just before adding the top of the tail cone) is a good time.

On the Roadkill Series models, it's less of an issue since servo mountings and pushrod routings are specified in detail in the plans. I did take pains on all of the models in that series to arrange the pushrods so that whatever reversing switches you needed on one of them would be the same for all of the other.

Set the servos in the locations and positions they will be in the finished model, and hook them up to the receiver and radio battery. If you have an electric that powers the radio from a BEC (Battery Eliminator Circuit) in the speed controller, then make sure the motor is disconnected, or at least remove the prop.

Check each control linkage and note which way the pushrod moved for a control motion. It's not a bad idea to actually write down a little chart:

Rudder:  pull for right  (meaning that if you pull forward on the pushrod, the rudder swings to the right)

Elevator: pull for down

Spoilers: pull for closed

etc....

Now, turn on the radio (make sure you are sufficiently far from any flying sites that doing so will not "shoot down" anyone flying nearby, including park fliers), and move each stick command in turn. Note which way the servo moves, and from that, which side of the servo the output arm needs to be on to agree with the chart you made for the pushrod motions.

The last step is to figure out how to arrange the servo mountings for the neatest and tidiest installation, with the best support for the pushrods and the least amount of clutter, best crash worthiness (for example, avoid putting the expensive, fragile receiver in front of the big, heavy battery unless there is sufficient structure protecting it), and best weight distribution to avoid having to add lead to the nose for C/G requirements. Since it's usually easier to move the C/G back than to move it forward, I usually start with everything as far forward as possible, unless another arrangement is specified in the instructions.

Other things may also need to be considered.

For example, on the 2-m Chrysalis sailplane, it's nice to have the radio battery removable for charging, or to install a new one at the field during a flying session. This means being able to get the battery out easily. However, the Chrysalis uses a closed top to the nose above the battery compartment to prevent the battery from coming out accidentally in flight (batteries have been known to depart the airplane due to centrifugal forces during launch). The only way to get the battery out is to slide it aft, out from under the nose cover.

Now, from a C/G standpoint, two servos are generally heavier than one modern receiver, which would argue in favor of mounting the servos behind the battery, with the receiver behind the servos and in front of the leading edge bulkhead, F2. However, that means running the pushrods past the receiver, and (more importantly), to remove the battery you would need to first remove both servos. This is obviously a bad arrangement in a whole shopping list of ways. Instead, it works much better to stuff the receiver (wrapped in sponge rubber) in behind the battery, then mount the servos behind it and ahead of F2. To remove the battery, lift out the receiver (leave all the cables connected), then slip the battery out. The receiver is light enough that the cables and the friction from the padding should be able to keep it attached to the airplane if the hatch pops off on launch.

Once you've thought through all of these sorts of things, and mapped out where everything needs to go, you may find that you need to rearrange some pushrods to get the cleanest run to each servo and the best support points for the pushrods. This is precisely why you go through all of this BEFORE you close up the fuselage. Once all the internal arrangements are taken care of, remove the radio until it's time to permanently install it later in the construction sequence.

Just like good flying, good building relies on planning ahead!

Don Stackhouse
DJ Aerotech