new problem with servo setup

[drdarren]

i am new to the trex 450. i transferred my spektrum receiver from my blade 400 to the trex. i attached the servos as directed and they are not working correctly. i tried various configurations and now everything is working except the elevator. it is reversed so when i move my right stick forward the swash plate tilts backward. if i reverse my setting for that servo, everything else gets messed up.

any ideas?

[uneverno]

Hey Drd.

There may be some method to the madness, but I couldn't tell you what it is.

I too am new to the 450 (and more so CCPM), but I'm using JR radio gear. I had to play with both the servo reversing and with the swashplate mixing functions to get the swash to move appropriately for every input. Every time I changed one thing, the swash reacted completely unexpectedly, i.e. pitch was reversed, so I switched it, and then the aileron servo was moving with it... This is, I presume, because with CCPM the three servos act interdependently, so if you change one thing on one servo, it will affect the other two. How that works, however, is a mystery to me.

I'm not at the radio now, but as I recall, the settings I ended up with were:

Mix Rev
Ail -60% N

Ele 60% R

Pitch -60% N

I think...

(Sorry, I was trying to create a table, but it's not lining up so well.)

Logically, one would assume from that set up that if I changed the Ail and Pitch to +60% and set the Ele at Normal, the result would be the same as what I have, but it's not. I'm guessing here, but I would think that has to do with how the servos are oriented in the frame, the arms of the two front ones being pointed outside the frame, toward the swashplate, so one is upside down in relation to the other, and the rear servo being pointed inside the frame, also toward the swash, so it's all kinda screwed up in relation to the other two.

I did not adjust the mix percentage from 60%. That means full servo response for each servo on my radio, and I get no binding in any direction from any of them with a level swash top to bottom on the main shaft when applying pitch. If you care to sort through it, you could probably get an idea what the other servos do if you were to set mix on any given servo to 0 and then apply stick for that servo. Again I'm guessing, but I'd think the selected servo should be unresponsive, and the other two should still do what they've been told.

I'll leave it to someone else to explain the geometry...

The 450 manual shows how the swash should react for a given stick input. I played with it until they all did what they should. Change a couple things at a time and see how it reacts. That's completely counterintuitive to problem solving, but I couldn't come up with a better way to do it. Bit of a game of cat and mouse, but it did come together in the end.

[drdarren]

thankyou for your advice. you did help me get on the correct path. i found a similar answer on another site. i reversed my swash setting for the pitch, changing it from 80 to -80 and it seems to be working fine.

[uneverno]

Cool,

I'm just figuring this out myself, so it helps to try to answer someone else's questions. It forces me to look at it from a new approach.

Why various radio manufacturers choose different numbers (60, 80, 50) to equal 100% is beyond me, but...

Glad I could help. Your question helped me noodle it through too.