3G wiring setup test

[330fo]

There are a lot of discussions about the Aling 3G wiring setup here using only one connector to power the unit and servos. I believe the wiring setup must be designed with thoughtful considerations. These concerns about the 3G bus trigger my curiosity. So I setup some tests to see what is going on.


First, the Micro-resistance meter is used to get the resistance of the single wire. Less than 20mΩ. Pretty good！

Then, record the current of the 700N with 3 DS610 servos (in swashplate position) using EagleTree. The total current under the extreme 3D maneuvers (at least it is my monster flight) is showed as the attached file "Eagle Tree.bmp"

The purple line is the current. As shown, the highest current is less then 5AMP. So … Is it good or …? To make it simple to catch on, the other small test will answer.

Let’sput 5AMP current to pass through the wire. The voltage drop is only 97.5mV. Therefore, the voltage drop will never exceed 200mv even for the Top Gun’s supermanuvers. Besides, if you have 10 AMP current on the wire, it is just mildly warm only.

I think it can explain why the single wire design is desinged in Aling 3G - simple and adequate.

These concerns are proved to be not necessary, about the low voltage due to single power wire might lead to system failure. If there still are something abnormal in the power system, instead of worry about the 3G wire, it might be better to check if the function of the aging battery, servos or the BEC work well or not.

[MrMel]

Your measuring the wire without the PCB/Solder, that's not the biggest problem, with some very dubious soldering quality, that's where the problem is, hence the problem with single wire.

Plus, EagleTree isn't good enough for this type of measuring, you need better equipments, peaks are higher then 5amp, eagletree has 10samples per/sec,you wont catch high peaks with it.

Lengthy thread over at RCGroups by some manufacturers about stall and start current on servos.

edit;
For sample; some (including friends of mine) which have had issues, ran A123 packs, here I have measured drops at the servo on a non 3G setup with 8717 when doing pitchpump on the bench, only using a single cable from the pack


as you can see even with a single cable from the pack it don't drop very much to cause issues, so the single cable itself isn't the problem.
And as you can see the peak draw happens in less then 5ms, so your eagletree will most likely not catch such peak.

[panzlflyer]

Youre findings go against all we have found out in the Giant scale community.
Simple it may be but its definately Inadequate and has no redundancy.
And MR Mel is right, the Eagletree doesnt catch spikes.
Simply charge a pack with a JR style connector and feel how warm it gets at the Connector at 3amps.

[HiroboFreak]

If you need a high speed scope to catch the peaks, doesn't that tell you that the duration of spikes (burst) isn't long enough to cause an issue?

Has somebody tested the unit pulling (for eg) 12 or more amps continuous & recorded how long it took for a failure to occur, if at all?

I understand all the figures & that it's "not good enough" in theory, but I've had many flights on mine, with zero issues. (AR7100R, both Align DS610's & JR DS8915's @ 8v)
Surely if this is a problem Align's pilots would have had failures during testing & the unit simply wouldn't have been released.

Has there actually been any failures directly attributed to the small wire theory?

The proof is in the pudding.

[MrMel]

If you need a high speed scope to catch the peaks, doesn't that tell you that the duration of spikes (burst) isn't long enough to cause an issue?

Not really, specially as there is no capacitors in the 3G (compared to others)
It takes only a few ms to cause a brownout.

[HiroboFreak]

OK, but has anybody actually tested it & conclusively proven it to be an issue?

[MrMel]

For those that crashed with "heli started to do piroflips by it self" its a good candidate (happened to my friend) since he's sensor cable was good and secured a brownout is the most likely cause, and he's powersource was A123 which does not drop as much by it self.

[Heechee]

Originally Posted by MrMel

For those that crashed with "heli started to do piroflips by it self" its a good candidate (happened to my friend) since he's sensor cable was good and secured a brownout is the most likely cause, and he's powersource was A123 which does not drop as much by it self.

A123 voltage drops a lot faster than LiPo voltage when the battery gets close to being empty.

[MrMel]

A123 voltage drops a lot faster than LiPo voltage when the battery gets close to being emp

In this case the pack was nowhere near getting empty.
Plus, no brownout on RX side, just In or after the input into the 3G which makes me think poor solder on the PCB of the 3G.

[JesusFreak]

Speaking of Capacitors, is it worth attaching one or two of the Spektrum capacitors to the system in an extra channel to provide a little extra insurance, or is this just a waste of time? I have a few laying about for my 450.

About to take my 500 out for a maiden today. I am using all Align servos, so I've wired the power leads to the servos directly, and I'm using a CC BEC. I'll have a report late today with some luck.

[330fo]

hr hr …

I am the heli hobbyist to shear fun of the flights with everyone, not the NASA expert to guarantee the success of the MARS exploration. The EagleTree is my Hubble due to the limited budget as a poor labor. If your guys have the supper weapon, it will be our pleasure to see the beauty of the black hole.

BTW, yesterday I put 8715 on 700N, and found the current was around 3AMP. Definitely much lower than DS610. Just for your information.