In a RT motion and data system, what is the best variable handling structure(s)?

Question

I built a system that applies motion control to two axes and also takes data from a third axis encoder. 
The program structure is parallel timed loops (one motion control loop, one data collection loop, one host communication loop) with front panel.
This is targeted to a RT target; there is no host program.
Now I am using global variables to pass information between the loops and for exchanging information with the front panel indicators and controls.  I think this is a suboptimal solution.  I am considering the following changes:
1) For communicating variable values (such as commanded velocity and position) to the motion loop, I will replace the global variable structures with onboard variables in the motion card memory.
2) For saving the data collected from the third axis, I will use an RT-FIFO structure in the RT controller memory.
3) I will eliminate the front panel from the RT program and create a separate user interface program targeted to the host PC.  Communication between these programs will be accomplished using the Simple TCP/IP Messaging Protocol as described in this document:
http://zone.ni.com/devzone/conceptd.nsf/webmain/0986799C984500F886256F170079411E
Global variables will be replaced with Motion onboard variables.
Before I start this chore, am I following the best practice?  Any advice on improving any aspect of this plan?
My System:
Windows XP on P4 PC ethernet to
PXI-8187 RT Controller
PXI-7350 Motion Control board
(2) servo axes with quadrature feedback
(1) additional quadrature encoder used as measuring probe
I do not have a DAQ card in this system.
Thank you!
Laine

Answer 1

Thanks Kristi.  I understand your recommendation.
Some of my variable instances are 4 or 5 SubVIs deep.  For instance, the main high priority loop calls MOVE.vi which calls CALC_ANGLE.vi, which calls CALC_MOVETIME.vi which calls CALC_VELOCITY.vi which uses the variable Initial_velocity.  If Initial_velocity is received from the host in the main program, passed to the high-priority loop using an RTFIFO, then bundled and kept in a shift register, what is the best way to get that information down where I need it?
Not only will I have to redeclare the RT-FIFO in each subVI, but I will also need to pass the reference value cluster down the chain as well?  This sounds messy and computationally expensive to me.  So my choices might be
1) Eliminate subVIs and bring everything to the top.  This is a rather large program, so could make quite an extensive top vi if all code is in one place.
2) Use onboard variables to store and pass values.  Are these less deterministic than RTFIFOs?  What is their primary purpose if not to pass data, or are they just to be used with motion card onboard programming?
3) Use global variables, but I think these are not deterministic.
4) Bite the bullet and pass the variable cluster down through the SubVI chain.  Is there an easier way to do this than what I describe above?
Have I made any bad assumptions or overcomplications?
Thanks.
Laine