Read through this part of the text and see if you determine a more applicable test for the radio than using an ohm meter. The test I am referring to is one that should be done before any flight with really expensive models, at least before first launch of the day. This test could have been done after the crash and even before buying a new antenna to determine if the 'loss of conductivity'" affected range (hint) In a message dated 11/26/99 << A few weeks after this event I heard about the unfortunate crashing of two Cobras, one after another by the same pilot. The second hand explanation for the crashes I heard was that the Tx aerial had no conductivity from the second segment on. This prompted me to check my Tx aerial. 200 ohms! This was measured with the aerial extended fully with the probes at each end. I checked each segment and found that each joint has a fairly equal portion of the resistance. I ordered a new aerial immediately and on receipt I checked it and found as I expected, zero (so small I can't measure) resistance. The aerial was the original supplied with the transmitter and is about 5 years old. I don't think my usage could be considered high. The appearance of the brass contacts inside the aerial would suggest to me that the problem is not age but the amount of use. It appears to be mainly dirty. I suggest anyone who has a transmitter aerial that is getting on a bit or gets a lot of use should check it or replace it. Cheap insurance at $40 or so. I am going to mark the new one with a date to replace it, probably in two years time and also check it from time to time. >> An interesting story but, has some holes. Why not clean it instead of buying a new antenna? How often should we invest in that cheap insurance? A new antenna every time? (this last piece about buying a new antenna made the crasher feel better about the crash but didn't solve a thing) Hey I have crashed more than most modelers, so I know this fix,,,sort of like an aspirin for crashing -- buy something :-) Simple cleaning of the antenna with alcohol to remove the oils collected by hands and dirt held there by that oil, fixes the contact thing. I do mine after flying a dusty trip. I simply extend the antenna and wipe it with an alcohol wipe (sort of like the prepackaged towelettes you get at rib joints:-) About once a year, I fill a soda bottle with alcohol then drop the ant. in and shake it. Amazing how much dirt collects inside....when you fly power, not so much with sailplanes. HOWEVER, I can see how after losing an expensive plane guys look for a 'mysterious' solution to explain the crash, but the TX antenna thing in this scenario should be suspect to any upstanding Vulcan. That is there is no logic. IF the TX antenna would have been the culprit we all would have been warned of the possibility from YK :-) AND the DIRTY TX antenna idea is so easily proved or disproved. YEP you guessed it and were probably thinking it when you read the scenario, and no the sky is not falling....cuz a simple RANGE check on the ground would have proven or disproven the dirty antenna+loss of range cause for the crash. He could have done it after the crash or at anytime. THERE is a more glaring clue to a 'range loss' in the statement "The aerial was the original supplied with the transmitter and is about 5 years old. I don't think my usage could be considered high". He doesn't state whether or not he has had his TX module or RX tuned in the last five years.... I am probably correct in guessing he has had them serviced each of the 5 years,,,,just like the rest of us :-) I hope you can see how various component problems could have STACKED to produce a failure (not this one) which would get blamed on a 'mysterious' cause like this dirty antenna solution. His post continues with these clues. I recently had the misfortune to destroy an Ellipse 2V. I had been practicing speed runs and had completed several prior to the problem. 1) On a subsequent speed run I had completed the three turns and the model was heading directly back toward base A about 30 or After the completion of one of the runs I experienced a brief loss of control of the model which resulted in a momentary roll to the left followed by control being reestablished. This occurred at 50m or so altitude and was not experienced again so I dismissed it as just one of those things. 2) 40m from base B in smooth level flight at quite high speed (it was a fairly neat run) and about 3m altitude when the model suddenly rolled and dived into the ground. Total disbelief doesn't adequately convey my feelings at the time. Initial discussion on the probable cause included flat battery, interference and structural failure of a joiner or something. 3) The battery was fine and all connections checked out OK. Interference is something that is very hard to determine. Remember he had range at other times, did the dirt build up in the antenna connections finally (during that particular leg of the run) finally become critical to cause a loss of range? Lets do some deductive investigating from the clues posted. (After all I think we all agree that crashing due to equipment failure is pretty serious stuff and for years the catch all explanation was "I GOT HIT," when in reality there were many reasons for crashes that never got found or fixed and so some we still fall victim.) Clue #1. He had 'range' (supposedly) prior to this speed run. And from clue #2 the 'hit' only happened during a speed run. And from this clue he was closer to the ground, which meant less time for the TX to RX to regain RF contact, that is IF there was actually a loss of RF. That there was a loss of CONTROL is evident, loss of RF is not evident. KEEP in mind that the RF comes from the Transmitter. His post assumes that the RF got weak due to a dirty TX antenna. How many of you reading differentiated between the loss of RF output versus the loss of servo control? In the story, the 200ohm thing implied a loss of RF output power from the TX that resulted in the crash. If that were true, the after crash test would have shown and still should show NO CONTACT between the TX and RX components. But it didn't, or at least the post didn't mention that. AT the very least it implies a loss of range but at-long-range wasn't when the first symptom or the crash happened. A dirty antenna is logically not likely to cause an intermittant symptom, certainly not a directional thing, and not one that is pending on speed of the aircraft. An open solder joint to the TX antenna would if jiggled, but that's not part of the story. >From both clue#1 and clue #2 a specific condition existed. High aircraft speed. I believe the real clue is there and it is what set up the conditions that produced both clue 1&2 and ultimately the crash (altitude was probably a factor in the crash but not in conjunction with any RF output related sense). Clue #3 3) The battery was fine and all connections checked out OK. Interference is something that is very hard to determine. The battery was fine. All connections checked out OK..... Well lets all sleep tight! :-) Not. A while back I got all excited about a device from RC Direct (even did an article in RCSD) called the Blinki. It is a very cool and tiny gadget that detects Signal glitches (different from RF) AND on board Power glitches AND records and displays the LOWEST voltage that the on board system saw during a flight! The one short coming I found in the Blinki is that it worked! Bozo read about it and got just as excited and ended up with the same disappointment after doing lots of testing and talking with the designer in Germany. IT WORKED. Yep it caught and recorded Signal glitches and Power glitches seen by the 'on board' system. Course the problem with it in our understanding of the words and things we use in our hobby. Like above where I talk about loss of RF output versus loss of control. When I first got the Blinki, I set out to test it in a ship. I peaked charged a 4 cell pack of 'GordyCells' (2000mah Sanyo SCRs) with my Infinity Charger and then turned on my fully assembled open class ship. The packed had a voltage of nearly 6volts no-load after peak and so I figured it would be a long time before I would see a Power glitch or decline in voltage. WAS I wrong, and so was BOZO. Bozo was very interested in on board voltage/power as he was USA F3B Team Manager and wanted the most power for his team's airplane's servos possible. On first deployment (on the bench) we both experienced the same recorded symptom! A total loss of power to the system or at least low enuf to trigger the Blink's Red Power light (not a good thing to have on in your plane:-) "What the heck? This thing is junk!" we both howled from different parts of the USA. We scoured the instruction sheet which discusses some reconnecting that can be done on the Blinki for various types of NiCads due to their personal discharge characteristics (huh? you say! Yep, I discuss some of that in an RCSD article "Coming to Terms with NiCads" quite a few years back now, E cells verus R cells versus standard cells). Anyway, I had it set for the cell type I was using as had Bozo, and in any case the setting would result in a total power drop reading. I suspected the cause but Bozo chased down the German and he made it clear.... Why MULTIPLEX has those funny and expensive connectors on their servos and battery connections. You see what the Blinki was telling us was true. When a high load was applied to the system, the weakest link in the system broke down (for the period of the extreme load). One or many of the connectors would overload and the connection decayed. I guessed at it by testing with smaller packs and in systems with less powerful servos, the symptom would go away. Bozo did actual testing by removing connectors and hard wiring all of the systems connections, he found no power glitch recorded and some amazingly power-filled servos too. BACK TO CLUE #3 3) The battery was fine and all connections checked out OK. Interference is something that is very hard to determine. The first part is Opinion,,, at best. His statement about Interference is a Truism, but has little to do with the story, since it didn't discuss 'Interference' as a culprit, but is a warm fuzzy way of ending a story like this. Because the ACTUAL cause is 'hard to determine' doesn't mean its okay to dismiss the fault to just any cause, in fact its more likely better to simply say, "I don't know," versus using some mysterious but plausible factor as the culprit. Deductive investigation is hard when it comes to determining cause, mostly because we aren't all scientists disciplined in various specialties of our TX/RX/Airframe systems. But what the heck, its fun to try to figure things out. :-) So taking what information and mixing it in a bowl of experience that I have I think that a better wild guess comes from the one FACT offered in the story. That of course was that the 'glitch' happened during the speed run, and that the crash happened at about 3m or 12' altitude. I am gonna say that either high frequency (NOT high amplitude) vibration (low amplitude/high freq buzzing of the airframe or a surface) set up an onboard power failure in a connection (probably power not just servo but could have been in say a Ruddervator servo or aileron servo, not flap) did the planes in. Altitude caused the wreck. The first 'hit' happened higher, that gave the plane time to change vibrations possibly due to attitude (stopped or dampened fluttering surfaces) and had enuf time to get back power. The second flight wasn't high enuf to allow for reconnect and recovery. If you have some plausible argument for this post, feel free to post it to me off line :-) If you just want to argue with me, don't bother posting :) IF you can back up a different resolution to the cause of the crash with logical, tested explanation like mine, post it on line. But I think you'll have to get up pretty early in the morning to do so :-) Gordy RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
