How can I firmly attach a Technic triangle to a turntable? I found a couple good technic triangle designs over on brickengineer.com. For example:  


  

How can I firmly attach a triangle to a large turntable?  

  

Details:


Really I only need to attach parts at the points of an equilateral triangle. These triangles are for example only; Solutions don't necessarily need to use these specific triangle designs.  
The setup should be able to rotate while bearing a small amount of weight (hence the turntable).
Have to say I'm not a big fan of the triangles you've already posted. In my opinion the half beams on the corners are too close together, causing stress on the elements.
Triangular technic designs are certainly possible, the following elements are useful: 

https://www.bricklink.com/v2/catalog/catalogitem.page?P=10288



https://www.bricklink.com/v2/catalog/catalogitem.page?P=57585