This is regarding a Chrysalis II. I have installed two new high-tech HS-50 servos. The cases are both parallel to the bottom of the wing, however, when I install the servo arms, they do not line up with each other.

I have adjusted them on the shafts, but am still unable to get them to line up. The tip of the arms are separated approximately 1/8 of an inch. Any suggestions?

From : Don Stackhouse

First of all, make sure they are centered. Plug them both into the radio, turn it on and then check for proper operation of the servos. Make sure both servos are in the "spoilers closed" position, then unplug the battery and turn off the transmitter.

If you still can't get the servos to match each other, you're probably looking at a difference in the centering of the two, or else you are using the wrong servo arms.

The spline that holds the servo arm to the output shaft has an odd number of teeth, 29 or so for the HS-50 if I remember correctly. What this means is that if you took a four-arm output arm assembly, and stuck it on the servo four different times with a different arm pointed as close to straight "up" as possible, the locations you would end up with for each different arm would be slightly different from that of each of the other three. Assuming that all four arms are the same length, you should pick the one that's closest to pointing the direction you want when the servo is centered.

Some four-arm assemblies have two opposite arms of one size and the other two opposing arms of a slightly different size. However, the same principle applies, just use the arm that is the correct length and that gives you the closest to the desired angle.

Once you've determined which arm to use, check if the other arms get in the way of anything over the full range of servo travel. If they don't, just leave them there, in case you need them on some other airplane in the future. However, odds are they will hit something, so just clip off the unused, interfering arms right next to the central hub (diagonal cutters work well for this). Just make sure that before you cut them off, you have identified the arms you plan to use. Now you know why servos usually come with extra arms!

Don Stackhouse
DJ Aerotech