Jon,

Attached is the data that I collected today. Point 12 was used as stationary and speed used was 1794 cpm. In the sheet, point 20, axis Z, the red phase value is indicating that it was unstable. It was bouncing around alot so I picked what I thought was the more stable value.
Also, there is another support angle that I collected data on , and it is show on the picture in the excel sheet. I did place a 2x4 under point 26, but did not see a drop in amplitude. Also, I noticed along points 15-18, I get a high 3X lobe pass freq (~13,200 cpm) at ~ 1.5 in/sec.

I tried to post a reply to my original post, but I'm getting errors.

Blower_Frame.zip (118 KB, 35 downloads)

Here is the animation. Looks like an imbalance causing the weak frame to flex on the outboard end of the blower. This is also causing the motor support to flex 180° out of phase with the blower support.
I'm surprised the added foot under the blower didn't produce better readings.

This message has been edited. Last edited by: Jon McFadden,

xRacerBaseBase3D.zip (2,420 KB, 32 downloads) 3D View

I would check your blower pulley for eccentricity and runout. The frame is weak because there is no corner bracing. This may be the reason for the possible misalignment of the pulleys.
Check the frame for a resonance in the "Y" direction (note the possible mode shape through 1,2,3,4,5) and the blower support around 26 and 27 in the vertical "Z" direction with bump tests.

This message has been edited. Last edited by: Jon McFadden,

xRacerBaseBaseTop.zip (1,592 KB, 18 downloads) Top view

I agree that it may be a weak frame. Anytime a structure looks bent or twisted in ODS animation the problem is either weakness or resonance. One way to tell for sure is to test for resonance (measure phase and magnitude during run-up or coast-down, negative averaging, peak hold bump test single channel or dual channel impact testing).

Another way to tell if the ODS animation indicates resonance vs. weakness is to look at the animation of another frequency (if available in the test data). If the frame is weak, the structure will show the same shape regardless of the forcing frequency. Consider this...If you were to mount a variable speed motor on top of a thin piece of sheet metal supported only at the corners, the residual motor imbalance would cause the middle of the sheet metal to vibrate vertically at any motor speed (i.e. same shape at all motor speeds). On the other hand, if the structure is resonating, the ODS will show a unique mode shape at each natural frequency.

The frame does look like it needs to be strengthened. Were there are other structural members on the frame that were not included in the test? It seems that the long rails should be tied together with cross bracing.

Is this frame up on isolators?

If forced vibration could be significantly reduced through balancing, alignment or more dimensionally accurate pulleys, the structure may not need to be modified.

A modal analysis would show all of the natural frequencies on the frame -- not just the ones being excited by forced vibration. Modal analysis is the first step towards correcting resonance problems. If a modal survey was completed and you owned the structural modification version of ME'scope software, you would be able to determine how to modify the structure to move natural frequencies away from forced vibrations.

Please let me know if I can help.

Thanks, Tony. Here is a picture of the machine xRacer is concerned about.