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Crash caused by faulty rx?

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Old 03-14-2015, 11:40 AM
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Default Crash caused by faulty rx?



OK, so I totalled my TwinStar today. Its 43
[SUP]rd[/SUP] flight turned out to be its last. Pity --- it was a fun plane. Iím puzzled as to the reason for the crash --- it wasnít pilot error.

Hereís what happened: on my final approach (my fifth flight of the day), the plane suddenly goes into a steep dive. I manage to recover, narrowly escaping a spectacular crash, and go round again for a new approach. Thinking I might have stalled the first time around, I keep the speed up. The same thing happens again: my TwinStar goes into a steep dive, while at the same time turning slightly to the right. It does not react to any stick input at this time. All I can do is watch helplessly as the plane turns itself into an ex-plane.

This was not a stall. In the past, Iíve been able to reduce the throttle to just above idle, and the TwinStar has floated in for a smooth landing every time. Iím thinking there might have been something wrong with the rx (a Spektrum AR7010. My tx is a JR DSX9). There are two reasons why I think the rx might be the culprit here, and Iíd like to hear your opinions on this.

First, this particular rx has always been exceptionally slow to connect to the tx after being switched on: around 15 seconds or more is the norm, which I find unusual. 15 seconds is a long time, as I think youíll agree. Once connected, though, it has worked fine.

Second, one of the throttle settings has on several occasions inexplicably changed without me having altered the settings on the tx. One day the throttles would be in perfect sync, the next day one throttle would be closed while the other was wide open. On such occasions, the only solution has been to adjust the throttle mechanically, i.e. by removing a servo arm and turning it a notch or two. I do not understand how this is even possible.

Both the rx and the tx batteries were fully charged when I started flying. I flew an inexpensive foam plane with the same tx after the crash --- three flights without any issues.

Any thoughts?
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Old 03-14-2015, 12:19 PM
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Sorry for the loss but it did give you a warning sign in the form of an extended bind time. That being said IMO it could still be either the TX or RX or it could have been your RX battery. When testing a RX battery it really has to be under load to full see the condition. Your bind issue could also have been having the TX too close to the RX during power up. I have always felt that the manufacturers could do a better job in instructing us on how to install equipment. Last week a fellow at the field was having lock outs. Upon inspection I found the RX antenna resting directly on the ESC ( electric airplane ). After moving the antenna he failed to do a range check prior to flying. Sadly his airplane was lost indicating it had another issue. Always route antenna away from other equipment and always do a range check before first flight, once every month and after changing anything that links to the RX.
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Old 03-14-2015, 10:02 PM
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Thanks for your comments. Yes, it could still be the transmitter. I guess I will have to keep an eye on it and just use it for foamies for a while. Fortunately, I have an old HiTec 35MHz transmitter to fall back on.
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Old 03-15-2015, 02:15 AM
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"Both the rx and the tx batteries were fully charged when I started flying."




Did you test your RX battery after the crash ? What was the reading under load ?
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Old 03-15-2015, 02:57 AM
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Good questions. Alas, no, I didn't test the battery after the crash. The battery was a fairly new (8-9 months old) Eneloop 2000mAh.
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Old 03-15-2015, 03:12 AM
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I try to test my batteries after something like this happens. It eliminates (or convicts) the battery as the source of the problem.
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Old 03-15-2015, 03:24 AM
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This is what the readings are today. Care to elaborate on the "under load" bit? I have a lot to learn when it comes to batteries, I'm sure.
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Old 03-15-2015, 08:12 AM
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My ESV has a load test button, to simulate actual useage. It's similart to the Hobbico tester in your pic.

I have one similar to the tester on the right, but it does not have a load test option.
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Old 03-15-2015, 09:19 AM
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You need to know the capacity of the battery. Measuring the battery with a voltmeter, even with a load, will only reveal that the battery may be good for the period of time that the measurement is being taken. A cycler is only way to determine your battery’s capacity. That number on the pack and the fact that you charged it before you flew is not the answer. Dan.
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Old 03-15-2015, 11:34 AM
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In this day and age its a shame you have to guess about a thing like this. A Chinese radio is able to record everything so you can later determine what happened,and it costs less than 1/3 of Spectrum or JR(Taranis)
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Old 03-15-2015, 01:04 PM
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Since the problem happened twice in the same general vicinity I would investigate the possibility of local interference. I know your not using 72mhz but 2.4kz also has its' problems.
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Old 03-15-2015, 02:47 PM
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Another possibility is that the transmitter antenna was pointing directly at the plane. This seems to be more of a problem when the plane is close to the ground. Been there, done that, suffered the consequences!
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Old 03-15-2015, 04:35 PM
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I have to agree. The 15 second binding time was a clue, which also could have been caused by a low battery or a bad receiver. The crash could have been a brown out on your receiver because of low voltage. Not sure what kind of a battery charger you have, but some of them will do a discharge cycle which will tell you what the voltage and storage of the battery. Good Luck, Dave
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Old 03-15-2015, 06:09 PM
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5 flights is still a long time on the 2000 mAh battery. Especially on 2.4.
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Old 03-15-2015, 07:04 PM
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Originally Posted by Desertlakesflying View Post
5 flights is still a long time on the 2000 mAh battery. Especially on 2.4.

Not by my experience, I have a YS 115 powered pylon airplane that has 5 servos and electric retracts. It's equipped with an 850 mah LiFe battery and I can do 5 heat races without issue. Each flight is about 75 mah. My 150cc Extra has 9 digital 400 oz servos and pulls 400 mah per flight on average. 2.4 pulls no more current then 72 MHz.
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Old 03-15-2015, 09:30 PM
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Gentlemen, thank you for your input. Who knows, it may have been the battery, despite the fact that it wasn't very old. I'll give it a cycle and see what I can find. The plane did have an onboard voltage monitor which did not show anything suspicious. I always wiggle the sticks before a flight to see how many of the LEDs will light up. It's just a rough guide, I know, but better than nothing.

Correct me if I'm wrong, but flashing LEDs on the rx would have indicated a brown-out, right? That is, if I hadn't turned the tx off as I was walking towards the crash site. That didn't occur to me until afterwards.

Nobody has commented on the detail that is the most puzzling to me, i.e. the fact that on this particular plane, the throttle setting would sometimes change spontaneously between flying sessions (I mentioned it in my original post). This to me suggests an issue with the tx, but something like this has only ever happened with this particular model memory --- no issues with any other model that I fly using this tx. The throttle setting would change to the extent that no amount of trimming would help; the only way to resolve the problem was to adjust it mechanically. This I find genuinely puzzling. Any thoughts on that?
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Old 03-15-2015, 10:34 PM
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If you are not using a 6v battery you had brown out. 5 flights on 2.4 with a 4.8v battery will get you a brown out.
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Old 03-16-2015, 03:33 AM
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Its always bad to see one tub in, but it does sound like battery to me also.
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Old 03-16-2015, 05:03 AM
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Originally Posted by junkjet View Post
If you are not using a 6v battery you had brown out. 5 flights on 2.4 with a 4.8v battery will get you a brown out.
Of course, that depends on how long the flights are. The fuel tanks on the TwinStar are quite small, not allowing longer flights than around 7 minutes. Previously, I've done 9 flights on one charge without any issues.
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Old 03-16-2015, 05:05 AM
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Originally Posted by dirtybird View Post
In this day and age its a shame you have to guess about a thing like this. A Chinese radio is able to record everything so you can later determine what happened,and it costs less than 1/3 of Spectrum or JR(Taranis)
I know. Too bad they don't come with a reset button as well, as in a flight simulator.
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Old 03-16-2015, 06:35 AM
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Hummm no one has thought of the battery switch, the voltmeter you have has a load built in. Per the pic it looks good.
switches are cheap replace it
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Old 03-16-2015, 07:01 AM
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The voltmeter readings you show under static load look good. I am assuming that is the voltage since the crash, you did not recharge the battery? If a brownout occured, it could have been caused by some electric short-circuit. I would check the servos and battery switch for any intermittent shorts. Just cycle everything and wiggle the wires. This might be related to the strange throttle setting issues. Also, on the throttle servos, check that the servo arms don't slip on the teeth. There have been cases where people accidentally put the wrong brand servo arm on the servo and it seems ok until it slips under load.

If you want to test the Rx, maybe you can put the suspect Rx into the cheap foamy you are testing to verify if the Rx is malfunctioning.

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Old 03-16-2015, 08:11 AM
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Originally Posted by hsukaria View Post
The voltmeter readings you show under static load look good. I am assuming that is the voltage since the crash, you did not recharge the battery?
No, I did not recharge the battery. The readings were done about 24 hours after the crash.

Originally Posted by hsukaria View Post
Also, on the throttle servos, check that the servo arms don't slip on the teeth. There have been cases where people accidentally put the wrong brand servo arm on the servo and it seems ok until it slips under load.
Now, that's an interesting thought --- I'll have to look into that.


Originally Posted by hsukaria View Post
If you want to test the Rx, maybe you can put the suspect Rx into the cheap foamy you are testing to verify if the Rx is malfunctioning.
Yes, good idea. Thanks for your input.
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Old 03-16-2015, 08:52 AM
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When I use these types of batteries I always use two of them and connect them together with a Y harness. Its only a few ounces more weight and cheap insurance.

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Old 03-16-2015, 09:01 AM
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I frequently run dual batteries myself, without a y-harness: I simply plug them into any available channel. Redundancy is always good. Didn't use dual batteries on this model, though.
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