RE: DX-7 related crash?

RE: DX-7 related crash?
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RE: DX-7 related crash? - 2/21/2007 5:32:46 PM

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A heavy duty 2-pole switch (e.g., MPI ones) should be fine. Use two siwtches/two batteries to get "quadruple" redundency on the switch component.

(in reply to digital_trucker)

RE: DX-7 related crash? - 2/22/2007 9:57:23 PM

3dsky

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I found that the Hanger 9 Load meter to be the best investment I have made. Digital servos draw more current under load and after bench testing a 8 servo setup using a 4 cell pack, 5 cell pack and a 6 cell pack I was amazed the drop in voltage when forcing only one digital servo. Small loads on the bench would drop the system voltage to 3.6 volts with pulses to 3.0 volts. This will make the receiver unstable. This bench testing proved to me that you must isolate the receiver voltage supply from the servos. (nothing new here but it helps to prove it first hand) After testing I have no problem spending the extra 150 bucks to have a bulletproof plane. I now use a power expander type unit in anything over 25%. My 27% and up I use the Smart Fly Sport unit and the super regulator on a 6 cell pack and love the results. Very clean and simple to set up. You should test your system like I did to prove to your self. Get a couple of you buddies to put loads on each surface and watch the Amps and Voltage. I also use the meter to test the Hitec programming on dual aileron servos. There is other systems for power management, Smart Fly has a good web site with good info on what works. Spektrum also has a Flight Log unit that will report the how well thew system is working. I am assuming this will help determine if you have a good installation. I would think the placement of the two receivers is important and this is a way to tweak the installation for best performance. Part #SPM9540

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RE: DX-7 related crash? - 2/27/2007 11:03:10 AM

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If you really like to be safe, eliminate the switches.
I started installing switches inside my planes, accessed through a hatch in the 80s because I didn't like the way they looked on my planes.
Now I never use them and my excuse changed to being safe.
I use deans connectors and simply unplug instead of turning off.
Sometime, take a switch apart and look at it.

DM

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RE: DX-7 related crash? - 2/27/2007 9:36:15 PM

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vintageflyer: That direct plug in cannot be beat it seems. I also think a person using Y hook-ups in anything should have a servo controller too check the Y harness out under load. Be good to have a good way to read current draw and voltage while testing. Just what to get for this is a good question also. Capt,n

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RE: DX-7 related crash? - 2/27/2007 10:08:05 PM

Red B.

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You should use some kind of Digital Power Switch that does not rely on mechanical contacts. Also, for applications with many high-current servos a Dual Power Servo Interface is the way to go.

Almost everyone I know that fly 1/4-scale aircraft and above (or jets) use this kind of equipment.

/Red B.

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RE: DX-7 related crash? - 3/9/2007 6:10:23 AM

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so i just got a call from the horizon hobbies tech yesterday. we had a long conversation, but what it came down to is this: he wasnt able to find anything wrong with the receiver- this was expected. i mean i've flown with this receiver for almost 100 hours and 99.9% of that time it was perfect. it only failed intermittently twice and both times for only a few seconds. any intermittent problem is extremely difficult to duplicate.

he suggested that it might be my batteries. that's what i thought also but for both batteries to fail exactly at the same time and only for a few seconds and come back online again afterwards..... i dunno.....

he also suggested to not use a y-harness to share one slot for both battery and a servo the way i'd done. he said that technically, there's nothign wrong with doing this, but seeing that i already had problems, he'd "keep it as simple as possible".

so the bottom line is that no one knows for sure what happened. all i know is taht it was an intermittent problem, actually occuring only twice (the second time causing the crash), and never duplicated again. the next time around, i'll be using 6volt, 5cell packs with at least 2000mah each, and heavy duty switches, one plugged into the battery slot in the receiver and one to the gear channel slot. i'll also be testing the current draw and voltage of the servos under load just before flying. i'm also using the receiver in my glow plane for about a month first before putting it into my big plane. after that if i crash again, i'll give up the hobby and play bingo instead! hahaha......

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RE: DX-7 related crash? - 3/9/2007 1:12:20 PM

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As has already been said...you are interested in Voltage under load and internal resistance of the pack. Remember adding conectors in between the pack/switch/bat increase the resistance and the final voltage/available current at the reciever.
Yesterday helpind do a setup we noted that 2 8411s binding slightly resulted in an amp draw of 2.3amps. A JR 1100 pack for example will not be able to sustain that for very long without dropping below 4v if its a 4.8 pack, neither can the popular but high internal resistance 2700, however the 1950 Sanyo can.
The newer breed of Nimh cell with low resistance are now pretty good.

(in reply to digital_trucker)

RE: DX-7 related crash? - 3/10/2007 12:53:02 AM

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I always use low-resistent Sanyo Nicad 5-cell packs, 1100mah, 1500mah etc. that are offered by RadicalRC. Also measure the mah consumption for an average flight for a setup. Always recharge after a certain number of flights that could consume half the total battery capacity. This scheme works for me just fine. Never had a battery related incident over 10 years of RC.

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RE: DX-7 related crash? - 3/10/2007 1:07:32 PM

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quote:

ORIGINAL: Phaedrus-MMVI

quote:

ORIGINAL: Andrew McGregor
I think you just didn't have a big enough battery capacity and browned it out.

You are confusing capacity with the ability to deliver voltage under load. Capacity has nothing to do with that. For instance I have some 1400 NiMH packs that have a very low internal impedance. Under a 1 amp load they will drop about .2 volts. I also have some 2700 NiMH packs that will drop nearly a full volt under the same 1 amp load. Twice the capacity, and nearly 5 times the voltage drop. It ALL has to do with the internal impedance of the cells in the pack. Bigger capacity does NOT always mean better performance.

Ditto- The capacity has nothing to do with internal impedance of the cells; nor the time and ability of the pack to recover after a transient load such as when you do a snap roll or other such maneuver.
When doing such maneuvers it's possible to have the pack voltage fall below the level that will sustain operation of the receiver. If the battery recovers fast enough the receiver will recover and the event would have been unnoticed by you. If the battery does not recover in time the receiver may drop out completely and require lots of time to recover, hence at this time you're in trouble.

The quote above addresses the internal impedance of the battery but there's also another parameter to be concerned about, that being the recovery time, or transient response of the battery. This parameter is usually associated with the battery family, NIMH, NICAD, or LIPO. NIMH, and NICAD are approximately the same in terms of recovering, LIPO's typically have a slower recovery.
The recovery time is directly related to the chemical makeup of the battery, and also temperature. In cold weather all types recover slower than in warmer weather.

This phenomena (transient loads, or conductive emi) has been a source of confusion for many fliers over the years. There was actually two types of interference one needed to be aware of before SS: conductive emi, and radiated rfi.
Radiated was both internally generated (metal to metal) and externally as when someone switches on your channel. This is no longer a problem with SS.

Of the two sources, only conductive emi remains as a source of concern when using SS technology.

The safest way to eliminate the conductive emi as a source of concern is to separate/isolate the receiver power from the servo power. This means that the receiver has its own battery and the servos have their own battery and they are completely isolated, except for the ground (black lead) of course..

(in reply to Silent-AV8R)

RE: DX-7 related crash? - 3/11/2007 11:02:33 AM

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I have noticed alot of flyers at my field have the 2 batt. into the rec. w/ no isolator. If you take apart the receiver, you can follow the copper on the board where the plugs are. The pos. and neg. are all parallel. That means if you have 2 packs, but one pack suddenly has a bad cell, that cell starts to load on both packs together.
Red, I'm not sure but do those digital power switches have an isolator in them. I do know that they fail to the on position, which I think is awsome! If they isolate also, I'll have to break down and start using them.

DM

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RE: DX-7 related crash? - 3/11/2007 11:30:02 AM

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Putting two packs in parallel does nothing to enhance reliability other than adding a redundant switch. As you say, if a pack should go south, depending on the mode of failure (cell shorted), it could take the other pack with it.

It's best to electrically isolate the receiver and servos, particularly in high dollar A/C.

The "failsafe" switches do not isolate as they conduct (bi-directional) in both ways. Yes, they do fail in the "on position" which is why I always use them.

There are various vendors that make isolators for this purpose, or if you're technically savvy you can do it yourself.

Here's a couple of examples:
http://www.i4cproducts.com/the_isolator.htm
http://electrodynam.com/rc/EDR-111/index.shtml

< Message edited by branded -- 3/11/2007 11:33:36 AM >

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RE: DX-7 related crash? - 3/13/2007 12:19:44 AM

jnmohn

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I just had a lock out the other day with a new DX7 on my World Model P39. I had about 10 flights on this plane with the DX7 when it locked up after about 1 minute into the flight. The plane was in level flight when it locked. All controls froze where they were. The plane started a gradual dive until it went in from about 300 feet. The receiver still works, but almost everything else was destroyed. I have another buddy that had the same thing happen on his plane two days ago. His plane almost hit someone when it went in from about 500 feet in the air. Pretty scary stuff! A lockout is not a good thing! I have had glitches, but never a total lockout. My plane was running of power supplied by the ESC and his was on a receiver pack.

Please figure this out before someone gets hurt!

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RE: DX-7 related crash? - 3/13/2007 1:04:16 AM

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quote:

ORIGINAL: jnmohn

Please figure this out before someone gets hurt!

it's not very likely that they will. people who are so all for 2.4 have it dead set that it's a completely fail free system and is 'indestructible'. with the attitude that the radio system will never be at fault makes them blind to the fact it's happening and they are failing.

kc

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RE: DX-7 related crash? - 3/13/2007 1:07:16 AM

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Looks like DX7 does have some bugs?

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RE: DX-7 related crash? - 3/13/2007 7:20:49 AM

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G'day Mate,
Maybe it has some bugs, maybe not, he didn't mention what receiver he was using, & almost all the problems have been with electric planes.
I bet it was a battery or power supply problem, I may be wrong, but that seems to be the common thread, with these electric planes.

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RE: DX-7 related crash? - 3/14/2007 10:52:09 PM

jnmohn

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Posted to another reply, but it also applies here:

I think we found part of the problem. I took three new Spektrum receivers (2-DX6 and one AR6000). It took two tries