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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Push-Pull Elevator Help!
07-19-2006 01:00 AM  14 years ago
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Chickenx10

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Ft Drum NY

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Push-Pull Elevator Help!
im just finishing up my raptor titan and i noticed that the push pull elevater is putting a very heavy load on the DS811 servo. Is this normal for the servo to sound like its being loaded? or should it sound just like the throttle servo?
Raptor 50 Titan / OS 50 Hyper / GY401 w/ 9254
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07-19-2006 01:08 AM  14 years ago
JAGNZ

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Auckland, New Zealand

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Make sure the links are silky smooth and that there is no binding at the max throw points. No, it should not load the servos excessively. On my R50, with this same setup, there is very little resistance. You may have to re-size the TT Ball Links, they are often too tight out of the bag. Get a link sizer or give them a little squeeze with some pliers to loosen them up....
Jason Greenwood

www.3dheli.co.nz
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07-19-2006 02:39 AM  14 years ago
xcellrc

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Mooresville, NC

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The geometry on the elevator push pull assembly on the titan seems to be wrong. I'm sure most will disagree with me on that. However, here goes my theory anyway. The angle formed by the center of the bellcrank, pivot at the ball link, then the servo pushrod should be 90 degrees at neutral. Also, the angle formed by the center of the servo arm, pivot at the servo ball link, then to the bellcrank pushrod should also be 90 degrees. That should be true for both linkages going from the servo to the bellcrank. If it isn't then you will have some binding. The only way to achieve that with the titan push pull assembly is to have the push pull rods parallel to each other. If you do that, then you have to greatly decrease the travel volume of the elevator servo (approximately 60%) The alternatives are to live with slight binding, and leave the linkages alone, or just disconnect one of the linkages to the servo. To prove to yourself that the geometry is wrong, disconnect one of the push pull linkages and listen to the servo...should be less load on it. Also move the servo to the extremes up and down. (again with one linkage disconnected) At center the ball link should line up over the ball on the servo arm. At the extremes of movement you will likely find that they do not line up by about 3/32". Well thats my theory anyway, I've been known to be wrong, but I've seen the exact same thing on a titan.
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07-19-2006 08:13 AM  14 years ago
Yug

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UK. Herts

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xcellrc - yes the geometry is not quite right.
The problem with reducing ATVs to 60% is that you loose torque as well as amplify any servo play.
In order to resolve this you need to bring the balls in closer on the disc to a radius of about 10.5mm and offset them forward by about 1mm each. This geometry will maintain equal throws on the pushrod at full elevator inputs so to binding force occurs. It also reduces the drive ratio and corrects for the amplifying effect of the push pull lever itself.

Vegetable rights and Peace
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07-19-2006 09:26 AM  14 years ago
andyp

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New Zealand

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Yug - thats perfect for the cnc push-pull, where a line joining the balls on the arm does not go thru the pivot, as per the usual TT item.

However - the pics I have seen of the Titan it looks like the push pull arm is changed with the balls and pivot making a straight line. Therefore no sweep necessary at the servo.

It is no problem coming in at the servo arm to allow 100% ATV. The two push pull pushrods do not need to be parallel.

Andrew
QuickUK Flight Team
Fromeco Regulators and Batteries
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07-19-2006 09:32 AM  14 years ago
Yug

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UK. Herts

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That makes a difference then. Probably best to fit a disc and balls at 180 degrees then with one link off the bull and held over it, rotate the horn and see how well the other one is tracking the ball. A bit a experimentation is well worth it here because in the long term, the servo/disc will be subject to far less lateral stress.Vegetable rights and Peace
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07-19-2006 03:56 PM  14 years ago
xcellrc

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Mooresville, NC

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Yug, You have it correct for the CNC push pull assembly. It can be made to work well because of the ball link offset in the bellcrank. The new titan linkage can not be made to work that way by offsetting the ball links on the servo arm. It isn't possible. In order for there to be no binding at the servo with the stock titan linkage, the pushrods will have to be parallel, no way around that. Decreasing the travel volume has obvious problems. Thats why I suggested disconnecting one of the pushrods. It works fine with just one rod on the push pull assembly. No binding, and when using a high quality servo, the push pull set up really doesn't do that much for you anyway.
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07-19-2006 04:28 PM  14 years ago
ADRYAN

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Stouffville, Ontario, Canada

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No More ChickenX Bashing... AMEN.

GJ Chick... keep it up.


A

.
DYNAX/OS91 : 9303/S649pcm : GY601/9251 : CSMRL10/9253 : 7.4vLipo/Regulator : KO2123s(ai/el/pi)
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