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Re: [Gumstix-users] Gumstix freezes in RC Plane
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From: Toner, B. <ben...@ro...> - 2007-05-08 09:07:23
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Hi Karthik, If you cannot mechanically mount the Gumstix in such a way to sufficiently reduce the vibration you may want to consider the following electrical changes. The effects of mechanical vibrations can manifest themselves as electrical noise in surface mount components, especially in capacitors. This is known as microphonic effect and due to a piezoelectric property of the substrate. http://en.wikipedia.org/wiki/Microphonic Capacitors that are used to decouple or smooth power supplies generally have to be high tolerance to ensure a clean supply. Regulators depend on an input and output capacitor to remain stable and if the capacitance varies the regulator may go into an unknown state - halting or damaging the device that is being powered by it. In order to keep the cost of Gumstix at the price we all like it to be, Ceramic capacitors have been used and these are definitely microphonic! I would assume the capacitors are of a 20% (or more) tolerance before vibration and unspecified when vibrated. Electrical considerations when designing for vibration usually involves using more expensive components that are non microphonic and have higher tolerance.=20 The first thing is to replace all capacitors involved in power regulation and supply filtering for tantalum type capacitors. http://powerelectronics.com/mag/power_multilayer_ceramics_tantalums/ While you are doing this, I would also add a low noise bypass capacitor to the regulator used on the GPSStix as it is optional and has been left out (presumably to keep cost down). Details are on the data sheet for the regulator, but this should probably be ceramic (not polarized) The second thing to do is use an epoxy resin on any components that have mass or a high center of gravity relative to the board they are mounted to, preventing vibrations from shaking components loose. A good starting point would be the Ublox. Also, you need to make sure that the hirose connector is held together well under all conditions. Either try bracing the connection somehow - or better still remove the connectors and directly solder the devices together with a single connector (placing it in resin after) After all that, my personal preference would then be to mount all sensitive electronics in a metal box where all electrical connections pass through EMI feedthroughs well mounted to the surrounding box (http://www.syfer.com/category_docs/filtgeninfo.pdf). This just helps any stray RF noise from motors etc stay outside the box. Admittedly some of these suggestions can be difficult to implement and it may be better to invest time in preventing the vibration from reaching the Gumstix though proper mounting! Good luck and if you do want to follow any of these suggestions, let me know what country you are in and I can point you to component suppliers. Ben -----Original Message----- From: gum...@li... [mailto:gum...@li...] On Behalf Of tim...@co... Sent: 08 May 2007 08:40 To: General mailing list for gumstix users. Subject: Re: [Gumstix-users] Gumstix freezes in RC Plane Hi Karthik, Sounds like a loose connection to me. Their is a lot a Gs in a model plane. To eliminate any issues from the engine or from the control rods try anchoring your plane_ or have a friend hold it_ gas it up all the way and move the control sticks all around. Then see if the gumstix is still working. Tim -------------- Original message ---------------------- From: "Karthik Balakrishnan" <k.i...@gm...> > Hi Dave, >=20 > Looking over your post again, I realized that I never mentioned -- I=20 > have a gas motor in the airplane, so there are no leads to put the=20 > caps! Would the moving metal parts of the engine cause enough current to affect the Gumstix? >=20 > First, I'm going to try shielding and see how that goes... >=20 > Thanks, > Karthik >=20 > On 5/7/07, Karthik Balakrishnan <k.i...@gm...> wrote: > > > > Hi Dave, > > > > I will try the caps + twisting wires + shielding and see how that goes. > > > > Thanks, > > Karthik > > > > On 5/7/07, Dave Hylands <dhy...@gm...> wrote: > > > > > > HI Karthik, > > > > > > > It's powered off its own battery pack (4xAA rechargeable for a=20 > > > > total > > > of 4.8 > > > > volts). > > > > > > It may be crashing because of EMF transmitted through the air from > > > the motor. > > > > > > Do you have caps across the motor leads? I recommend putting 3=20 > > > 0.1uF (or 0.01uF) caps on your motor. One between the leads, and=20 > > > one between each lead and the metal case on the motor. > > > > > > Putting a metal shield between the gumstix and the motor and=20 > > > grounding the shield can also help to reduce transmitted EMF. > > > > > > I had a similar problem on a robot I built where the processor=20 > > > board was directly over the motors. I had even added=20 > > > opto-isolators and used separate batteries, but the EMF=20 > > > transmitted from the motors was enough to disrupt the CPU. Adding=20 > > > the metal shield helped a bit, but the thing that helped the most was installing the caps. > > > > > > Also, the red and black wires from the battery should be twisted=20 > > > around each other if there is any length to do so. The same goes=20 > > > for the wires to any motors. > > > > > > Twisting the wires reduces the loop inductance, which in turn=20 > > > reduces transmitted noise. > > > > > > See the following links for some good tips on wiring and what not. > > > The 4QD guys are big in the battle bot stuff, but the same=20 > > > techniques apply equally well to all motorized devices. > > > > > > http://www.4qd.co.uk/serv/appnotes/machinewire.html > > > http://www.4qd.co.uk/serv/appnotes/RCWiring.html > > > > > > -- > > > Dave Hylands > > > Vancouver, BC, Canada > > > http://www.DaveHylands.com/ > > > > > > ------------------------------------------------------------------ > > > ------- > > > > > > This SF.net email is sponsored by DB2 Express Download DB2 Express > > > C - the FREE version of DB2 express and take control of your XML.=20 > > > No limits. Just data. Click to get it now. > > > http://sourceforge.net/powerbar/db2/ > > > _______________________________________________ > > > gumstix-users mailing list > > > gum...@li... > > > https://lists.sourceforge.net/lists/listinfo/gumstix-users > > > > > > > ------------------------------------------------------------------------ - This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ gumstix-users mailing list gum...@li... https://lists.sourceforge.net/lists/listinfo/gumstix-users --=20 Roke Manor Research Ltd, Romsey, Hampshire, SO51 0ZN, United Kingdom A Siemens company Registered in England & Wales at: Siemens House, Oldbury, Bracknell Berks RG12 8FZ. 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