B

Bill Phillips

Well Known Member
I have an Odyssey EFIS with Trio servos in my RV-8a. How do I set the pitch to center? When I conduct the ground test for pitch the elevator is way down from the HS. When I turn the AP on while flying she noses over into a dive that never self corects. How do I set the pitch to center or netural on the ground? Best regards, Bill
 
Hi Bill,
When you installed your pitch servo you should have had the elevators clamped in the neutral position. Then, with the servo arm in the "center" position, you adjust the length of your pushrod so it connects the servo and the elevator bell-crank without deflecting.

This is assuming that you drilled the hole in the bell-crank after clamping the elevators and lining up the servo arm (to neutral).

Basically, if you set all parts to the middle, or neutral position before drilling your hole in the bell-crank, you should only need a minor adjustment on the rod-end bearings (of the pushrod).
 
AP Servos w MGL

Sonny, thanks for the input, but I don't recall doing any of that when I set the servo arm and push rod. I followed instructions. You sure the computer don't set the arm swing somehow? On a certified system I once adjusted and saw set up, a control knob on the control head was turned to set the pitch and a button pushed to remember the setting. The knob swung the servo arm and centered the elevator. Seems like the MGL efis should be set as easily? Best regards, Bill
 
I don't think its in the instructions. I did the same thing and had to backtrack and re-rig the servo. Also, the outer hole on the servo arm won't provide enough torque. Clutch will slip & kick out the servo. So make sure you rig neutral elevator with servo arm centered and that the servo arm will not over-center when using the middle hole.
 
Center or neutral positions are only used if you are using PWM servos (these do not provide any kind of position feedback and in fact, the AP does not even know if they are connected). PWM servos should not be used with pitch control (although provision is made to use them).

For all other servo types you can select, the servo simply engages in whatever position it happens to be when you activate the AP - the AP simply takes control from that point, regardless of your aircrafts attitude.

If you engage while stationary with the controls approximately neutral, you should see the controls moving slowly in whatever position would be required to "get on track" and "get on altitude". As there is no resulting reaction from the aircraft you will see the AP trying harder and harder.

With the Trio servo, you can adjust the slipper clutch (see servo manual). This can help to prevent slip with relatively light torque applied. You should adjust this so you can overpower the servo in flight but it must not be too light so the servo slips in normal flight or during normal manouvers.
For my own aircraft (before I used MGL servos), I needed to adjust the bank servo slipper clutch before it would hold nicely.

Rainier
CEO MGL Avionics
 
Thanks everyone for your fine input.

I redrilled the bell crank and moved the servo pushrod to neutral. I'll fly tomorrow and test. Thanks again, Bill
 
Oh yes, forgot to add:

With Trio servos, servo arm position is important - it has an active range of around +/-40 degrees but will travel more than that until it hits a mechanical stop. Your neutral position should be somewhere close to the center position of the servo arm travel.

With MGL servos there is no restriction - they will work to just under +/-180 degrees for bank and pitch (although +/-50 to 60 degrees is probably the practical limit for a bell crank arrangement) and 360 degrees for yaw. They can be engaged in any position, does not matter.

Rainier
CEO MGL Avionics
 
You must log in or register to reply here.