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Old Mar 19, 2012, 02:22 PM
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Yes, Another Newbie Radio Question

Iíve only been into RC flying for a little over a month. I did a lot of reading here on RCG before making my first purchases, knowing that a good deal of what I was reading related to personal preference.

My first radio is a Spektrum DX7. I based that on information I found here, on the recommendation of my LHS, and the fact that one came along at a very good price. So far it has worked out pretty well, but I do have concerns.

My concerns are based on the frequent issues I read about with regards to crashes and lost aircraft due to lost signal. This may certainly occur to more than just Spektrum, but that brand seems to bear the brunt of the exposure.

As I said, my DX7 experience to this point has been pretty good, however I have seen my quad (my only RC aircraft at the moment) do some strange things at times. Iím not saying that these oddities have anything to do with an actual problem with my radio system, and could very well be linked to configuration, lack of experience, or outside influences. However, with everything Iíve read, it does make me wonder a little.

So in terms of this loss of signal problem, is it an issue with Spektrum, 2.4 GHz in general or something else? Is there a reliability issue with Spektrum, or can I expect this same phenomenon to occur with any 2.4 system I buy?

I do not want to start a ďbrand warĒ and not sure if my question has a simple or complex answer. I would just like to do my due diligence in keeping my aircraft (and the people around it) safe to the best of my ability.
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Old Mar 19, 2012, 02:53 PM
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The DX7 is a good radio made by JR. Its link is pretty good if you fly around few other fliers.

If you fly on a crowded field, you'd be better off having a true frequency hopping system like the later DSMX or any Futaba or Hitec system.

All 2.4ghz systems can experience brownouts due to low battery voltage.
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Old Mar 19, 2012, 03:00 PM
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I have about 5000 flights on a DX7 and haven't had an issue yet.

They are the biggest seller (in the US at least) and a lot of them are sold to brand newbies who often don't get any training from experienced people so it's often hard for them (or anyone else) to tell pilot error from setup error from actual radio error. A common scenario: buy BNF or RTF plane. Take it to a random empty place. Fly. Stall. Radio problem - obviously. Another common scenario is that I find an unofficial field and everyone tells me that there is a Bermuda triangle where radios randomly fail. And I know where it is before they tell me! It's on approach - of course!

My own experience is that the number of apparent radio issues dropped dramatically as I gained experience. All while using the same equipment. If I had changed equipment I probably would think the new stuff was better, but it probably would have been an illusion caused by my increasing experience.

I just saw a Team Futaba (sponsored) pilot loose a heli and he thinks it was the radio but I don't think we know enough to say it was an actual "Futaba radio problem" as opposed to everything else that could have gone wrong.

Plus you have to allow for the fact that a lot of people will crash (or hard land) a plane, see that all the servos move, declare everything good and fly.

As for 2.4GHz in general. There were lots of horror stories around here about how bad/mysterious it was - until most people were using it. Then it was more like: Oh yeah, it just works. Stories like that are better when the person hearing the story has little direct experience with the subject.

The number one issue, especially on older receivers which didn't have the quick reconnect feature, are brown-outs caused by BECs that just weren't powerful enough to handle the loads. I've stuck with switching BECs from quality vendors and always allowed for at least an extra amp of BEC rating vs what I could measure by loading the servos and I've never had that problem.

BTW yesterday, 4 of us went up after a thunderstorm and we all agreed it was the strangest air we had ever seen. Everything was just jerking around in every conceivable direction. It was a hoot! As long as you weren't too concerned about your vehicle. You couldn't feel all this turbulence on the ground where we were standing.

Bottom line - enjoy it!
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Old Mar 19, 2012, 03:04 PM
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Quote:
Originally Posted by seefest View Post
The DX7 is a good radio made by JR. Its link is pretty good if you fly around few other fliers.
. . .
But then, the OP states that the LHS recommended that radio, so if he got it from the LHS he probably got a new radio. DX7 has been discontinued for a year or so, so he might have acquired a DX7s which already is a DSMX radio and has nothing in common with JR.
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Old Mar 19, 2012, 03:25 PM
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I noticed a DX7 on display recently in a hobby shop. Perhaps they didn't move that quickly once the DX8 came out. The owner of that shop has grumbled to me a couple of times that Horizon comes out with new stuff and improved versions without warning him not to stock up on the old stuff,

But you could be right that he meant DX7S.
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Old Mar 19, 2012, 04:24 PM
A Snickering Hound
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Thanks to all of you for your input. It has given me a clearer picture of what to expect from my radio system and 2.4 GHz in general.

To clarify my transmitter model, it is the DX7. Although my LHS does sell Spektrum, I opted for a used one that popped up here on RCG. While I'm happy with that purchase (aside from the concerns in the original post) I must admit I did not do my homework with regard to the different versions of the DX7 that are available.

Dave, you make a very valid point about the inexperience and after an unusual event takes place, not being able to adequately diagnose its cause. This is most certainly the situation that I find myself in. This will hopefully improve with time, experience, and education.

Moving forward, I see I need to understand which of these older receivers *may* cause an issue. I don't do any long-range FPV or the like (much later I hope) and use a 6100e. It came with my quad so I guess I need to investigate its history a little.

Anyway, thanks again.
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Old Mar 19, 2012, 05:13 PM
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One receiver I would stay away from would be the AR500. I've had two STB on me within 6 months and my dad had one crap out not long after. They replaced it with the AR600, which by all accounts is a decent receiver.
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Old Mar 23, 2012, 05:25 PM
TigreJohn
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Not sure, but if you purchased a used DX7, it may be an early model where the receivers did experience "brown outs". Best solution to avoid such is to replace your receiver battery with a 5 cell pack and/or get the add-on receiver capacitor that they created to alleviate the problem.
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Old Mar 23, 2012, 10:25 PM
A Snickering Hound
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Thanks jj. I was not aware of an issue with early DX7's. I'll have to do a little research and see if specific lots and/or mfg dates are published somewhere. Wonder if there is a way for me to tell if that capacitor was already added.
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Old Mar 23, 2012, 10:40 PM
どうもありがとうミスターロボット
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Quote:
Originally Posted by seefest View Post
...All 2.4ghz systems can experience brownouts due to low battery voltage...
But some receivers and brands of radio systems are a lot more prone to it than others. To imply that they're all the same in this respect is misleading.

Bottom line: Find out the requirements of your specific electrical setups and power them accordingly.
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Old Mar 23, 2012, 11:01 PM
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Originally Posted by Muddie View Post
Thanks jj. I was not aware of an issue with early DX7's. I'll have to do a little research and see if specific lots and/or mfg dates are published somewhere. Wonder if there is a way for me to tell if that capacitor was already added.
There were no issues with early or later DX7 transmitters. What jj is implying is that the early Spektrum receivers did not have fast reconnect feature and sometimes it took up to 6-7 seconds for the receiver to reconnect if it reboots. The cure is either to upgrade it to the latest firmware which has the quick reconnect feature or use power system that will not let the receiver reboot.
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Old Mar 24, 2012, 08:51 AM
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Quote:
Originally Posted by Muddie View Post
Thanks jj. I was not aware of an issue with early DX7's. I'll have to do a little research and see if specific lots and/or mfg dates are published somewhere. Wonder if there is a way for me to tell if that capacitor was already added.
There is no such issue with the DX7. It was purely a matter of long reboot time for the receiver if it lost power. Test the receiver by turning power off and back on again. If it takes more than a second to regain control, you have the old firmware and need to send it back to Horizon Hobby for a free upgrade. Do not use a Spektrum receiver with the old (pre-2008) firmware.

The DX7 is an excellent transmitter. I've used one since 2007 with no issues at all. Good results with Spektrum generally for five years. Only bad experience was with an AR500 receiver that was replaced by Horizon.
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Old Mar 24, 2012, 10:07 AM
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Originally Posted by Wrend View Post
But some receivers and brands of radio systems are a lot more prone to it than others. To imply that they're all the same in this respect is misleading.

Bottom line: Find out the requirements of your specific electrical setups and power them accordingly.
Not misleading at all. All brands of receivers will brownout if voltage drops below certain levels. This level may vary 1/2 V or so, but if you are having voltage drops that close to brownout, then your power supply is inadequate.
Regardless of the system, your power supply should be the best it can possibly be for the application.
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Old Mar 24, 2012, 10:18 AM
TigreJohn
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Quote:
Originally Posted by Daedalus66 View Post
There is no such issue with the DX7. It was purely a matter of long reboot time for the receiver if it lost power.
A clarification. True, there was no issue with the early DX7 transmitter. The problem was with the early receivers. Yes, the receivers would have long boot times when you applied power to them. They also take a long time to reboot with their power being interrupted. But they would also go into a full length reboot if the input voltage dropped to I think it was 3.6V or lower This could happen in the air with a partially discharged pack and heavily exercised servos, especially if they were digitals. Hence the need for 5 cell packs and/or the capacitor which plugged into one of the servo connectors to avoid that "brown-out" situation.
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Old Mar 24, 2012, 10:31 AM
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Originally Posted by seefest View Post
Not misleading at all. All brands of receivers will brownout if voltage drops below certain levels. This level may vary 1/2 V or so, but if you are having voltage drops that close to brownout, then your power supply is inadequate.
Regardless of the system, your power supply should be the best it can possibly be for the application.
In reality that "1/2 V" (or in some cases, more) can make a huge difference depending on the total electrical setup and it's requirements.

As just one example: http://www.rcmodelreviews.com/horizons_tricks.shtml (He seems to take the credit for discrediting this intentionally[?] misleading video, but some of us here at RCG had in a couple threads much earlier.)

There are real scenarios, where because of even just a small difference in the minimum operational voltages of different receivers, one receiver could likely fail and it would be very unlikely for the other one to. Though I would also of course discourage marginal setups in either case.

As I said: Find out the requirements of your specific electrical setups and power them accordingly.

For some small setups that needed little power, and didn't pose a safety risk, 3S AAA NiMH cells and 1 cell LiPo have worked sufficiently for me on some of the standard 2.4GHz receivers.
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Last edited by Wrend; Mar 24, 2012 at 02:50 PM.
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