Helicopter build - Help with spacing a ball on a servo horn (trigonometry problem)


Can I please appeal to the community with greater trigonometry knoweledge than myself to help solve this little problem I have come across?

During my build of an Arducopter Traditional Heli on a Gas powered Raptor 90, I re-positioned the servos for a 90 degree ECCPM set-up to help counterweight a camera gimbal up front and there is a difference in throws between the two rear servos driving the swash through a 90 degree bellcrank, and the front servo driving the swash directly!

Could someone please help me work out how far out I should have the ball on the horn's of the two rear servos so that they give the same range in motion as the front direct drive servo?

The servo side of the bell crank is 24mm, the output side is 33mm and the ball on the front direct drive servo is 17mm out, so with that info how far out should I position the ball on the servos driving the bell crank?

Thanks for the time!!~


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hi ben have had a quick look at your pictures.
Firstly you need to get all the links at 90 degrees to each other.
After that as long as the bell cranks are of equal length there should be no changes to the throws of the input to output ratio.
It looks though, as if the bell cranks are too far forward, the rods are not parallel to the main shaft at mid way servo.
I have not worked with 90degree ccpm, but if i'm correct the back two servos stay still when you apply elevator and the front one stays still when you apply aileron. They all move when you apply collective pitch.
The only issue i can see after that is the servo links for the servo to bell cranks are a few degrees off centre, this will cause an error. I'll talk to you later on tonight.

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