[Firebug-cvs] firebug/doc/chassis chassis.tex,1.3,1.4

[David M. D. <do...@us...>]

Update of /cvsroot/firebug/firebug/doc/chassis
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv28012

Modified Files:
	chassis.tex 
Log Message:
Added Kevin's notes on wiring harness.

Index: chassis.tex
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RCS file: /cvsroot/firebug/firebug/doc/chassis/chassis.tex,v
retrieving revision 1.3
retrieving revision 1.4
diff -C2 -d -r1.3 -r1.4
*** chassis.tex	5 Jul 2004 18:13:37 -0000	1.3
--- chassis.tex	8 Jul 2004 00:32:20 -0000	1.4
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*** 19,22 ****
--- 19,102 ----
  \section{Wiring harness}
  
+ To create wiring harnesses for the motes, the issues that were encountered
+ can be separated into roughly two sections: crimping the connectors
+ and connecting the connectors to the battery cases.   
+ 
+ 
+ \subsection{Crimping the connectors}
+ 
+ 
+ In order to utilize the Molex power connector on the mote, we
+ purchased 50058-8100 Molex crimp terminals and 51021-0200 Molex
+ crimp housings.  To accommodate the size of these two parts,
+ we found it best to use 26 AWG wire.  In order to crimp these
+ connectors, we were officially supposed to use a specific Molex
+ crimping tool.However, the cost of this tool is roughly $180,
+ making it quite a hefty investment.  Thus, we instead went with
+ a $7 crimping tool from a nearby electronics store, and did our
+ best to make working connectors.  But because of the size of
+ these parts, crimping the terminals was very difficult, and even
+ now there is no telling just how robust these connectors are.
+ 
+ \subsection{Connecting the connectors to the battery cases}
+ 
+ The battery cases provided with the motes caused a predicament
+ when it came to connecting the connectors to an actual power
+ source, which in this case meant batteries.  For some of the
+ battery cases that no longer had wires extending from them, we
+ tried to solder wires to the cases, but to no avail.  The cases
+ just were not designed for soldering wires to them.  And even
+ for the cases that did still have wires connected to them,
+ there were still issues to be addressed.
+ 
+  To join the wires and form one piece that went from the battery case to
+ the connector, solder was first applied on each pair of wire separately
+ (the two red and two black wires) and then reinforced altogether with some
+ plastic heat-shrinking material.  This process, however, had some flaws.
+ First, the diameter of the heat shrink (expanded diameter of .187”)
+ could not fit over the crimp housings, so the heat shrink had to be
+ placed on the wires prior to soldering.  It is important to note that
+ since the heat-shrinking material only shrinks up to 50% of its expanded
+ diameter, a larger heat shrink would have been too loose to properly
+ insulate the two sets of wires together.  Thus, we could not use heat
+ shrinks with a larger diameter to remedy this problem.As a result,
+ since we had to place the heat shrink on the wires before soldering,
+ the length of heat shrink that we were allowed to use was limited
+ by where the joining of the wires would take place.  This was rather
+ disappointing, because we had hoped to cover up the two wires entirely
+ with heat-shrinking material so that the two sets of wires would act as
+ one.  The second flaw we found was that the soldered wires could not
+ just be wrapped in heat-shrinking material, because a short would then
+ exist at the soldered areas between the red and black wires.  To prevent
+ a short from happening, the two options were to either first wrap each
+ wire separately with heat-shrinking material and then wrap both of these
+ with a heat shrink, or to use electrical tape and first insulate each of
+ the wires before applying the heat shrink.  The former could not be done,
+ however, because we did not have heat shrink with a large enough diameter
+ that would insulate the two heat-shrinked wires.  The latter proved to
+ be quite difficult too, because the heat shrink barely (and in some cases
+ failed to) fit over the taped-and-soldered wires.   
+ 
+ \subsection{Suggestions}
+ 
+ 
+ From these experiences with creating wire harnesses for the
+ motes, we have a couple of suggestions to make.  The first
+ one is regarding the Molex power connector on the mote board.
+ It would be nicer if Crossbow could use a larger (and possibly
+ structurally different) connector so that we could manually make
+ more robust connections.  Secondly, it would be very helpful if
+ Crossbow could provide better battery cases.  Since there is a
+ Molex power connector on the mote board, Crossbow should devise
+ a way for people to utilize that connector instead of just the
+ soldered connections.  Using the current battery cases for this
+ purpose is very difficult, largely because of the different sizes
+ of the wires, and the difficulty of insulating them properly.
+ It would be great if Crossbow could either provide battery cases
+ that would allow us to connect our wires directly to them (instead
+ of having to find a way to couple our wires with existing ones),
+ or to maybe even provide a battery case that already has a molex
+ connector on the end.
+ 
  
  \section{Batteries}