hilleyja

My Feedback: (3)

Mike,

I'm setting up a Cap with dual elevator servos. I connected one to channel 2 and the other to channel 7. I am using a Futaba 9C. an 8-channel Hitec RX and dual HS-425s.

The 2 servos are mounted in the fuselage on either side of the rudder servo and the control arms point to the fuselage sides. Clearance between them and the rudder servo would make changing their directions very difficult and because of this I'm virtually forced to mix the channels instead of y-connecting them. This of course means that when I set the MIX up between elevator and channel 7 I have to reverse the direction of channel 7 in relationship to the elevator channel.

I've done this and my problem is I'm getting a significant difference between the 2 elevator deflections (difference will definetely effect the trim of the airplane). The push rods cross each other in the fuselage, they are of a nyrod design with a carbon arrow shaft as the sleeve -- virtually no side flexing, and they are virtually identical in size. Right now I'm attributing the deflection difference to the servo deflections.

Here's the rub: Neutral for both servos are not currently 90 degrees to the servo case. They actually point slightly aft of 90 degrees to the case. If I was to modify the clevis' so that they both are exactly 90 degrees to the case will I elliminate the deflection difference or is the difference due to one servo going in one direction and the other going in the reverse?

I'm asking this question but will not stand still -- I will be modifying the clevises to make them both 90 degrees to the servo case. I will also refine the hardware adjustment to get as close as I can to neutral on both servos without using the subtrims. Since I also own the Hitec servo programmer I will verify that the pulse widths between channel 2 and 7 are the same. Unfortunately, since these are analog servos I won't be able to adjust their deadpan.

I am asking A.M. at Futaba a similar version of this question because the TX we are talking about is the Futaba 9C. I will be asking her if there is anything in the 9C programming that I can use to bring the 2 servos deflections closer together.

MikeMayberry

My Feedback: (1)

I would use the sub trim to center each servo and adjust the linkage so the surfaces are neutral when the servos are at 90 degrees.

Mike.

hilleyja

My Feedback: (3)

Are you actually saying to adjust the servos to as close to 90 as I can get and then use sub trims to refine the adjustment? How consistent are the HS-425s when it comes to centering?

MikeMayberry

My Feedback: (1)

Yes, use the sub trim to get them to exactly 90 degrees then install the linkage and adjust it so the surfaces are at neutral.

The 425's have good/average centering, not as good as the 5-pole, coreless or digitals though.

Mike.

TOYMAKER

My Feedback: (6)

Dont you want the servo arm to be 90 degrees to the angle of the pushrod? If its 90 degrees to the servo case then there will be differential. At least thats what happened in mine when I set it up with duals. You will get more movement in the up elevator then down because of this differentail. All linkages should be 90 degrees to the control surface and push rod. Then use subtrims to get that 90 degree angle if your servo arm wont allow it on the splines. I also crossed my pushrods so I could get a straight shot to the elevator horn. I used 3/16 carbon fiber rods with 4-40 titanium ends. Very solid and it elimated a mushy pushrod problem I had that was causing a violent snap to the right because of one elevator not moving equally to the other half. But in order to do that the pushrod will come off the servo at about 15 degree angle.

hilleyja

My Feedback: (3)

This is the same recommendation I got from A.M. at Futaba. I also have my push rods crossing in an 'X'. I did try it with 90 degrees to case and flew it this evening. I was not dissatisfied with the flight but more refinement is needed in the elevator control (also need to reduce the sensitivity because even on low rate the elevator was very touch with this airplane.)