[Firebug-cvs] firebug/doc/chassis chassis.tex,1.13,1.14
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[Firebug-cvs] firebug/doc/chassis chassis.tex,1.13,1.14
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From: David M. D. <do...@us...> - 2005-11-17 00:33:08
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Update of /cvsroot/firebug/firebug/doc/chassis In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv18657 Modified Files: chassis.tex Log Message: More fix up. Index: chassis.tex =================================================================== RCS file: /cvsroot/firebug/firebug/doc/chassis/chassis.tex,v retrieving revision 1.13 retrieving revision 1.14 diff -C2 -d -r1.13 -r1.14 *** chassis.tex 27 Oct 2005 21:36:27 -0000 1.13 --- chassis.tex 17 Nov 2005 00:32:59 -0000 1.14 *************** *** 17,30 **** \title{Chassis and battery design for wireless sensor motes} ! \author{Kevin Lee\thanks{}, ! Alex Do\thanks{Grad. Research Assistant, Dept. Mechanical ! Engineering, University of California, Berkeley, CA}, ! David M. Doolin\thanks{Asst. Research Engineer, ! Earthquake Engineering Research Center, 1301 S. 46th ! St., RFS 451, Richmond CA 94804}, ! Nicholas Sitar\thanks{Professor and Director, ! Earthquake Engineering Research Center, 1301 S. 46th ! St., RFS 451, Richmond CA 94804} ! } \date{\today} \maketitle --- 17,31 ---- \title{Chassis and battery design for wireless sensor motes} ! ! %\author{Kevin Lee\thanks{}, ! %Alex Do\thanks{Grad. Research Assistant, Dept. Mechanical ! %Engineering, University of California, Berkeley, CA}, ! %David M. Doolin\thanks{Asst. Research Engineer, ! %Earthquake Engineering Research Center, 1301 S. 46th ! %St., RFS 451, Richmond CA 94804}, ! %Nicholas Sitar\thanks{Professor and Director, ! %Earthquake Engineering Research Center, 1301 S. 46th ! %St., RFS 451, Richmond CA 94804} ! %} \date{\today} \maketitle *************** *** 73,77 **** This paper reviews the design process and technical issues for creating such a chassis. ! \section{Background} The architecture of a typical wireless sensor consists of the --- 74,78 ---- This paper reviews the design process and technical issues for creating such a chassis. ! \section{The Mica mote} The architecture of a typical wireless sensor consists of the *************** *** 107,111 **** antenna that plugs into an MMCX connector on the mote board. ! While a Mica wireless sensor is functional "out-of-the-box," the default configuration is not rugged enough for practical use. Network testing and deployment requires the motes to be physically handled, --- 108,112 ---- antenna that plugs into an MMCX connector on the mote board. ! While a Mica wireless sensor is functional as-shipped, the default configuration is not rugged enough for practical use. Network testing and deployment requires the motes to be physically handled, *************** *** 135,151 **** adhesive, and still many of the aforementioned problems occur. ! \section{Design Objectives} Early on we identified the following design objectives in a mounting chassis: \begin{itemize} ! \item Tool-less; requires only hands and possibly a coin to open, disassemble, reassemble (rapid and simple) \item Separation of modular components: sensing, power, mote, antennas \item Wiring harness to separate power connection \item battery cage design to accommodate different battery candidates ! \item Supports mounting by: screw, strap, zip-tie, magnet \item Injection moldable for low-cost high-volume production \end{itemize} ! \section{Design for Assembly} >>Boothroyd references --- 136,157 ---- adhesive, and still many of the aforementioned problems occur. ! ! \section{Mica Mote Chassis} Early on we identified the following design objectives in a mounting chassis: \begin{itemize} ! \item Tool-less; requires only hands and possibly a coin to ! open, disassemble, reassemble (rapid and simple) \item Separation of modular components: sensing, power, mote, antennas \item Wiring harness to separate power connection \item battery cage design to accommodate different battery candidates ! \item Supports mounting by: screw, strap, zip-tie, velcro, magnet, hook, or similar ! technology. \item Injection moldable for low-cost high-volume production \end{itemize} ! ! \subsection{Design for Assembly} ! >>Boothroyd references *************** *** 161,164 **** --- 167,227 ---- -chamfers on the battery clip + + \subsection{Design for Injection Molding} + + -straight-pull design + + -avoiding undercuts + + -constant wall thickness to avoid shrinkage + + -shelled design + + -strapping slots ribbed for rigidity + + \begin{figure} + \begin{center} + \includegraphics[width=3in]{figs/exploded_view_2.eps} + \caption{An exploded view of the ``candy bar'' chassis + used for the controlled burn test at East Bay Regional + Parks Fire Department, Lake Chabot.} + \label{fig:exploded_view_2} + \end{center} + \end{figure} + + + + A prototyped ``candy bar'' chassis machined from acrylic + is shown in Fig.~\ref{fig:exploded_view_2}. + + + \begin{figure} + \begin{center} + \subfigure[Front view.]{\label{subfig:candy_bar_injection_moldable_front}% + \includegraphics[width=2.5in]{figs/candy_bar_injection_moldable_front.eps}} + \subfigure[Back view.]{\label{subfig:candy_bar_injection_moldable_back}% + \includegraphics[width=2.5in]{figs/candy_bar_injection_moldable_back.eps}} + \subfigure[FDM front view.]{\label{subfig:fdm_front}% + \includegraphics[width=2.5in]{figs/fdm_front.eps}} + \subfigure[FDM back view.]{\label{subfig:fdm_back}% + \includegraphics[width=2.5in]{figs/fdm_back.eps}} + \caption{Injection mold design, and prototype using FDM technology.} + \label{fig:cbim} + \end{center} + \end{figure} + + An injection moldable chassis, as shown in + Fig.~\ref{fig:cbim} was designed with the ??? software. + + \begin{figure} + \begin{center} + \includegraphics[width=3in]{figs/fdm_assembled.eps} + \caption{Assembled mote using FDM prototype.} + \label{fig:fdm_assembled} + \end{center} + \end{figure} + + + \section{Wiring harness} *************** *** 170,181 **** \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 --- 233,247 ---- \subsection{Crimping the connectors} ! Each mote in the Mica family is equipped with a small, ! plastic Molex jack as an external external power plug. ! This allows clean separation of an external power supply ! such as a battery to be independent of the mote. ! 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. Instead we used a \$7 crimping tool from a nearby electronics store, and did our best to make working connectors. But because of the size of *************** *** 183,186 **** --- 249,262 ---- now there is no telling just how robust these connectors are. + The Molex power connector is more fragile than the existing + soldered connection to the battery pack in the default + Mica configuration, and too fragile to use for repeated + assembly and disassembly of the motes. The advantage over + soldering is that it's possible to replace just the + battery component in the field very quickly, since there + is no need for a soldering iron. + + + \subsection{Connecting the connectors to the battery cases} *************** *** 194,245 **** 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. --- 270,307 ---- 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 0.187 in) 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. *************** *** 247,285 **** ! When considering whether to use the Nickel-Cadmium (Ni-Cd) ! or Lithium Ion (Li-ion) batteries, we took into account ! several factors, focusing on its ease of use and whether ! there would be detrimental effects to the environment ! given the proposed usage of these batteries. Since ! firefighters will be placing these battery-powered ! devices on their helmets, one issue is to have the ! batteries be as light as possible. In this case, the ! Li-Ion battery chemistry is much lighter than the ! Nickel-Cadmium one, providing less of a burden on ! firefighters. Now the idea of using rechargeable ! batteries was so that firefighters would not have to ! frequently open up the device and replace the AA ! batteries. However, Ni-Cd batteries have what is ! known as ``the memory effect,'' where partial ! discharges will lead to a decrease in the capacity ! of the battery. Thus, to combat the memory effect, ! it is recommended that the Ni-Cd batteries be fully ! discharged before recharging. If we were to require ! firefighters to completely discharge the batteries ! first each time, then this idea of using rechargeable ! batteries would not be that much more convenient than ! having to replace the AAs. Moreover, if the batteries ! were to only be used for motes, then they would never be ! completely discharged. Luckily, Li-Ion batteries ! do not have this effect, and it is even recommended that ! only partial discharges be made before recharging them. ! Lastly, another concern was what effects the batteries ! could have on the environment if they were burned up. ! Again, the Li-Ion batteries prove to be the better choice, ! as Ni-Cd batteries are toxic and harmful to the environment. ! Li-Ion batteries do not even contain free lithium, thus ! making them much safer for this particular use. Given ! these considerations, Li-Ion batteries are much more ! suitable than Ni-Cd batteries for this project. \subsection{Combining the Battery with the Motes} --- 309,347 ---- ! When considering whether to use the Nickel-Cadmium (Ni-Cd) or Lithium ! Ion (Li-ion) batteries, we took into account several factors, focusing ! on its ease of use and whether there would be detrimental effects to ! the environment given the proposed usage of these batteries. Since ! firefighters will be placing these battery-powered devices on their ! helmets, one issue is to have the batteries be as light as possible. ! In this case, the Li-Ion battery chemistry is much lighter than the ! Nickel-Cadmium one, providing less of a burden on firefighters. Now ! the idea of using rechargeable batteries was so that firefighters ! would not have to frequently open up the device and replace the AA ! batteries. ! ! ! However, Ni-Cd batteries have what is known as ``the memory effect,'' ! where partial discharges will lead to a decrease in the capacity of ! the battery. To combat the memory effect, Ni-Cd batteries must be ! fully discharged before recharging. If we were to require ! firefighters to completely discharge the batteries first each time, ! then this idea of using rechargeable batteries would not be that much ! more convenient than having to replace the AAs. Moreover, if the ! batteries were to only be used for motes, then they would never be ! completely discharged. Luckily, Li-Ion batteries do not have this ! effect, and it is even recommended that only partial discharges be ! made before recharging them. ! ! ! Lastly, we were concerned about what effects the batteries could have ! on the environment if they were burned up. Again, the Li-Ion ! batteries prove to be the better choice, as Ni-Cd batteries are toxic ! and harmful to the environment. Li-Ion batteries do not even contain ! free lithium, thus making them much safer for this particular use. ! Given these considerations, Li-Ion batteries are much more suitable ! than Ni-Cd batteries for this project. ! ! \subsection{Combining the Battery with the Motes} *************** *** 296,369 **** especially a larger one, since the battery wires are larger than the ones used to attach the battery case to the Molex power connector on ! the board. (to be continued...) ! ! Ideally, it would be nice if we could use the one connector for the ! entire mote. This would leave us with three options: use the molex ! power connector, the adaptor jack, or a mini-USB jack. ! ! \section{Mounting} ! ! -strapping (velcro, zip-tie) ! ! -hooks ! ! -magnets ! ! \section{Design for Injection Molding} ! ! -straight-pull design ! ! -avoiding undercuts ! ! -constant wall thickness to avoid shrinkage ! ! -shelled design ! ! -strapping slots ribbed for rigidity ! ! \begin{figure} ! \begin{center} ! \includegraphics[width=3in]{figs/exploded_view_2.eps} ! \caption{An exploded view of the ``candy bar'' chassis ! used for the controlled burn test at East Bay Regional ! Parks Fire Department, Lake Chabot.} ! \label{fig:exploded_view_2} ! \end{center} ! \end{figure} ! ! A prototyped ``candy bar'' chassis machined from acrylic ! is shown in Fig.~\ref{fig:exploded_view_2}. ! \begin{figure} ! \begin{center} ! \subfigure[Front view.]{\label{subfig:candy_bar_injection_moldable_front}% ! \includegraphics[width=2.5in]{figs/candy_bar_injection_moldable_front.eps}} ! \subfigure[Back view.]{\label{subfig:candy_bar_injection_moldable_back}% ! \includegraphics[width=2.5in]{figs/candy_bar_injection_moldable_back.eps}} ! \subfigure[FDM front view.]{\label{subfig:fdm_front}% ! \includegraphics[width=2.5in]{figs/fdm_front.eps}} ! \subfigure[FDM back view.]{\label{subfig:fdm_back}% ! \includegraphics[width=2.5in]{figs/fdm_back.eps}} ! \caption{Injection mold design, and prototype using FDM technology.} ! \label{fig:cbim} ! \end{center} ! \end{figure} - An injection moldable chassis, as shown in - Fig.~\ref{fig:cbim} was designed with the ??? software. ! \begin{figure} ! \begin{center} ! \includegraphics[width=3in]{figs/fdm_assembled.eps} ! \caption{Assembled mote using FDM prototype.} ! \label{fig:fdm_assembled} ! \end{center} ! \end{figure} ! \section{Conclusions} --- 358,398 ---- especially a larger one, since the battery wires are larger than the ones used to attach the battery case to the Molex power connector on ! the board. Ideally, it would be nice if we could use the one ! connector for the entire mote. This would leave us with three ! options: use the molex power connector, the adaptor jack, or a ! mini-USB jack. + \subsection{Charger design and construction} ! {\em Kevin, a paragraph here would be excellent.} ! \section{Conclusions} ! \subsection{Wiring harness} + From these experiences with creating wire harnesses for the + motes, we have a couple of suggestions to make. ! \begin{enumerate} ! \item 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. ! \item 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. ! \end{enumerate} |
