The following is an [edited] email exchange sent between members of the SUS group on May 2nd 2012. I wanted to reproduce it here because (a) I don't want to lose it, (b) it'll be good to have a hyperlinkable reference, and (c) it might be of use to the more general audience.


Jeff Bartlett wrote:
------------------
Can you lend some guidance on the proper d1 values for the HxTS suspensions, by answering what is the tolerance range for the d1s?

Jeff Kissel wrote:
------------------
We demand the machining tolerances on all parts involved, such that the final physical d's have a tolerance of +/- 1mm, and that's what we've therefore pushed to have the assembly tolerances be. 

However, to see what we've done thus far, and compare that against how d1 affects the modeled transfer functions, I attach a comparison between the 4 Phase 1 HSTSs they've put together at LLO and three models: 
d1 = (nominal+3mm) 
      2mm (Nominal) 
     (nominal-3mm)] 
   = [5mm below M1 CoM]
      2mm below M1 CoM, Nominal
     [1mm above M1 CoM]

The plots show that 
- In the measurements, the 4 SUS were built (at whatever d's they were shooting for) *remarkably* consistent. 
- All degrees of freedom except for Pitch are pretty darn insensitive to d1.
- In pitch,
	- With the tolerance set to 2mm +/- 3mm, seems to encompass measurements well,
	- The measurements match models with a more negative d1 (with "higher" respect to vertical, i.e. blade tips up, or CoM down ) better that the nominal 2 mm
	- A model with d1 ~ 0mm (or [nominal - 2mm] ) is about where all the measurements lie. This is not explicitly shown in the plots, but I started making them using a d1 of nominal +/- 1mm, and worked my way up to three, and as I passed +/- 2mm, I saw that -2 mm matched the data well.
	- NOTE: that d1 ~ 5mm (or [nominal + 3mm]) seems to nail the highest frequency Roll mode, but goes in the wrong direction for Pitch... emphasizing that the models aren't perfect. 
	 
So, in summary -- do whatever Livingston does 'cause what ever d1 value and tolerance they use results in delightfully consistent transfer function results.

Robert Giglio wrote: [On "what Livingston does"]
--------------------
I've been shooting for a d1-value of between 2 and 3mm below the center of mass and I TRY to get them within .5mm of each other.  In practice, due to the discrete nature of the clamp swaps, I sometimes end up with more than that in roll (pitch is usually spot on because I can change weight on the intermediate mass).