Announcement

Collapse

Coupon

Posted 3/2/2019: 1st time shopper coupon $3 OFF any order. Coupon Code: NORD3
Shop Now (https://www.sadoun.com)
See more
See less

SD180PM Tensor matrix?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • SD180PM Tensor matrix?

    Hello, I am looking for the tensor matrix values for the six foot prime focus dish for motor sizing use. I used the equation y=x^2/(4*fl), where fl is the focal length, to generate the parabolic curve. I used the curve, in a Ruby plugin, for Google Sketchup to plot a 3d image of the 6 foot prime focus dish. The result is very realistic.
    I was able to find a program to convert skp files to a mesh STL (stereo lithography format) file.
    Using meshlab.exe (a product from brilliant source forge developers) there is a filter to calculate tensor matrix values. There is no mass for an STL file. However; knowing the area, an estimation for the mass can be made. However, I have no clue how meshlab.exe derives its inertia tensor. So far, my values for volume are about right. However my area is off by a factor greater than 2:
    Sorry, I cannot figure out how to show the formulas for area and volume. They are a png image, and cannot see the final result.



    My values:
    Mesh Area = = 1819.66 inches^2
    Mesh Volume = 24565.49 inches ^3



    Values from meshlab.exe:

    Mesh Bounding Box Size 71.819603 12.006600 71.819603
    Mesh Bounding Box Diag 102.275459
    Mesh Volume is 23991.791016
    Mesh Surface is 4429.372070
    Thin shell barycenter -0.000000 6.200392 0.000000
    Center of Mass is 0.000000 -4.022667 0.000000
    Inertia Tensor is :
    | 4125501.250000 0.000000 -0.012266 |
    | 0.000000 10187072.000000 0.000000 |
    | -0.012266 0.000000 4125501.250000 |
    Principal axes are :
    | 0.707107 0.000000 0.707107 |
    | -0.000000 1.000000 -0.000000 |
    | -0.707107 0.000000 0.707107 |
    axis momenta are :
    | 4125501.250000 10187072.000000 4125501.250000 |

    Any help is greatly appreciated.
    Last edited by Rob Ram; 05-04-2013, 09:01 PM. Reason: Correction
Working...
X