					Using DigiTrak Engine (Motor) Files
					Generated from RASP.ENG v2.5b
					with Rogers Aeroscience Data
					using MARK.EXE

While doing some simulation comparisons between DigiTrak and wRASP runs,
I discovered a problem when running DigiTrak with a set of motor files
that were generated from the lastest RASP.ENG file.  Also, note that
running the MARK.EXE program on the v2.5b RASP.ENG generates different
file names than described in the DigiTrak documentation.

The DigiTrak program and data set is distributed with an older version of
Mark Johnson's RASP.ENG file.  The later ones (v2.5b and subsequent)
contain data for Aerotech RMS motors that was contributed by the kind
folks at Rogers Aeroscience (RAS).  There is a slight difference in format,
however, that causes DigiTrak to crash when using these motors.

The original motor curves assumed the (0,0) point (zero thrust at time
zero) and did not contain this data value.  The RAS data tables contain a
zero time point that may or may not be zero thrust.  When the MARK.EXE
program is used to generate the motor files, it adds in the (0,0) point.
(Note that the (0,0) point is *NOT* included in the interval point count)
What DigiTrak chokes on is the two sequential zero time points and attempts
to execute a divide-by-zero, which causes an exception.

A work-around for this is to use 0.000001 instead of zero for the time step.
An example for the AT H128 follows:

file h128w_ae.eng as originally generated by mark.exe:

; Input data courtesy Rogers Aeroscience. 
155.791412 92.200005 1.500000 12 
0.0  0.0
   0.000    0.623
   0.100    157.281
   0.200    129.748
   0.300    129.748
   0.400    125.256
   0.500    125.256
   0.900    125.256
   1.000    120.808
   1.200    102.927
   1.300    44.747
   1.400    8.940
   1.500    0.000

file h128w_ae.eng as modified:

; Input data courtesy Rogers Aeroscience. 
155.791412 92.200005 1.500000 12 
0.0  0.0
   0.000001 0.623
   0.100    157.281
   0.200    129.748
   0.300    129.748
   0.400    125.256
   0.500    125.256
   0.900    125.256
   1.000    120.808
   1.200    102.927
   1.300    44.747
   1.400    8.940
   1.500    0.000

This should cause DigiTrak to work correctly.  By the way, problems with
this format are not unique to DigiTrak, early versions of wRASP also had
this problem with the RAS-generated files - they caused multi-stage rocket
runs to crash as well.  This was alertly picked up by MODELNET members
Gary Briggs and Darrell Mobley.  wRASP handles the different format files
during data loading.

.......Chuck Gibke

