View Full Version : Multiple pivot axis?

04-16-2012, 10:54 AM
I am working on my first attempt of a drop door and the setup will require that I have a servo arm rotating on the the X axis, and a linkage to a drop door that moves on the Y axis. The motion will require the linkage to pivot at the servo arm on the X axis but also slightly in the Y axis at the door as it opens.

I have the doors and servo arm moving fine but technically, the linkage is connected to both the servo arm and the drop door and pivots from both. Can you actually connect in 3dsmax hierarchy an object to more than one parent as it doesn't look like you can.

Is my only option to connect the linkage to the servo arm and try to have it move on the axis(s) it needs to appear to be connected to the drop door?

What would the suggested method be for completing this motion?

04-16-2012, 11:35 AM
Use a helper object in Max to get two pivots. The first pivot moves the helper and the helper moves the actual object.

04-16-2012, 11:54 AM
That seems to me to be essentially how I animate my servos. I parent the control horn to the aileron. It moves with the aileron. I parent the pushrod to the servo arm. I parent the servo arm to the wing. If I have a 20 degree throw on the aileron, I'll have the servo arm rotate 20 degrees. Then I set the aileron to full deflection, and rotate the push rod by whatever amount is required for it to be attached to the control horn at full deflection. In your case, you would animate your drop door seperately, just as my aileron is animated seperately.

04-16-2012, 11:56 AM
Maybe I'm not understanding your question, but couldn't you set it up the same way as an aileron connection?

04-16-2012, 11:59 AM
Maybe I'm not understanding your question, but couldn't you set it up the same way as an aileron connection?

Nah, that'd never work! :p

04-16-2012, 02:28 PM
Sorry for the confusion. I am a noob in the modeling arena and with working the physics in RF. I haven't done' an aileron connection either, which is what I will be working on after this one.

Am I following correctly that most of you are setting up an aileron connection as follows:
- Parent the servo arm to the servo
- Parent the pushrod to the servo arm
- Parent the feed horn to the control surface (drop door, elevator, aileron, etc)
- Set the pivots in 3dsmax
- In RF, setup both objects to move at the same time so that they appear to be connected

In the case of my drop door, the pushrod will both rotate as the servo arm moves but also it would move slightly on the Y axis because of how the door opens. Can I have an object move along more than one axis? Do I just have more than one NUP value with each axis listed in 3dsmax for the pushrod object?

dhk79: If there is a way to setup a hierarchy so that the pushrod is the only object that is set to move and that moves the rod which opens the door, I would suspect that to be the easiest. How do you setup helper objects in 3dsmax to do this?

04-16-2012, 02:35 PM
You can have the pushrod move on all 3 axis if need be. That is all set in the aircraft editor. You can look at any model with servos to see how that is done.

04-16-2012, 02:45 PM
You don't need NUP values to do what you wish to do. Just set the part to rotate on any or all 3 axes in the RF editor, like Andy said.

04-16-2012, 03:33 PM
You'll notice that a movable pod allows you to assign a servo to each axis of rotation. If you use your drop door servo in the X axis as well as the Y you can then set a maximum and minimum rotation for both axis and both axis will move from the same assigned switch.
The picture below illustrates what I mean. Notice the rudder servo is assigned for each axis of rotation. Above those you can see that rotation values are plugged in for X, Y, and Z.
In your case you would just need to assign a Y rotation servo (same as door drop servo) and then with the doors in the open position find the appropriate amount of Y rotation needed for proper alignment of the push rod and the control horn.

04-17-2012, 03:54 PM
Thanks for the help! I have it working perfect now. This was for my second model that I am working on, the FlyZone Sensei. I did just post to the swap pages my first ever full model, the FlyZone/Hobbico FW190A, for anyone out there that would like to get it and the RF 6 AV. Posts and ratings are welcome. :)

Aircraft: http://www.knifeedge.com/forums/downloads.php?do=file&id=16607
RF6 AV: http://www.knifeedge.com/forums/downloads.php?do=file&id=16608