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HelicopterFlybarless Rotor Head SystemsOther › Futaba's New GY750 system at tower with price.
02-21-2011 03:40 AM  6 years agoPost 101
basmntdweller

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Indianapolis IN

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Just because "factory" guys say it okay doesnt make it so, I seem to remember them declaring no problems with the 3g as well lol
I went through at least 60 gallons last season, equally split between my two stock 700s. One with a flybar and one with 3G. Just one wire from the stock regulator on both helis. No problems yet. I am also flying Spektrum and I haven't seen any holds or brownouts either!

Matt


Stupid people have no idea how stupid they are!!!

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02-21-2011 07:59 PM  6 years agoPost 102
Bruce2.5D

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Vancouver, Canada

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Re "No problems yet...", helis vary so much in their servos, FBL systems and the gains used, that one example doesn't mean 1 wire is a good idea.

Re the comments:
"Whether transients should be considered peak draw is debatable."
and
"FWIW, non of my current spikes over 3 amps lasted more than half a second."

Transients absolutely do matter. Human perception makes a 0.5 second scale seem normal, and the heli might respond on a 0.1 second scale. But the servo and FBL system live on a 0.01 second scale or faster.

A human 0.5 second scale only matters for battery drain. The pipe pressure analogy doesn't work, because the electrical equiv of pressure is voltage, amps is the equiv of volume flow not pressure.

Servo makers rate their servos in terms of speed, but acceleration (so torque and peak amp draw) often count for more. The FBL system can be sending command changes that will result in full acceleration, and full torque for 10ms many times a second. The higher the gain the more the twitches. That doesn't show up at all on an eagle tree but an oscilloscope will show 2-5ms voltage dropouts.

The capacitors in the BEC will typically only bridge that full torq load for 1ms or so. After that the voltage drops, so does torque. Below 3.5 volts odd stuff starts to happen, and below 3 volts microcontrollers start to reset. I've seen digital servos take 0.5 seconds to reset on the bench due to short brownouts. Often people think the tail let go, or they had a static problem. Their loggers will show nothing wrong.

Each connector is rated for a max of 3 amps - one modern digital servo after a sudden change! Even a 450 size heli will see very short brownouts (2ms) with a 3 amp BEC. A typical jumper + connector at each end might be 0.2 ohms, at 6 amps that's 1.2 volts drop right there.

Long story short, listen to Mr Mel on this one. Engineer for a peak load of 3 amps per digital heli servo.

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02-21-2011 09:40 PM  6 years agoPost 103
nickmcdonald

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new lenox, il

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I'm sorry but I find it funny every time I hear this argument. The jumper in a perfect world will have a resistance of ~0.008 ohms. The connector is actually closer to ~0.015 ohms. Total cable loss assuming JST connector on each end (not the case) is actually 0.038 volts per amp.

Now lets assume you fly in a perfect world with zero losses in each component and the receiver battery is capable of providing limitless power. Let's also assume you use a single JST connector/18 gauge lead to run from the battery to receiver. And you'll obviously need another connector to run from the receiver to the FBL unit, and yet another to run to the each Ail, Elev, Pitch and rudder servo.

5.6V Battery
Battery to Reciever - 12A load, 0.276V drop
Receiver to FBL (Single lead) - 12A load, 0.276V drop
FBL to Servo (per Servo)- 3A load, 0.069V drop

So your receiver see's 5.324V
The FBL Unit see's 5.048V
And each servos see's 4.9V

Luckily for us in the regulated lipo world we fly today the above situation is not that far off from the truth. The fact remains that in almost all cases, brown out's happen from either inadequate power, i.e, battery, or faulty connections.

So how much of a load would it actually take to produce a 1.2V drop?

Roughly 13 amps per servo, or 52 amps total. That is of course if the wire and connector could even stand up to that. Which is what this whole thing is about right?

Look, it's fine if you want to argue against the whole one connector issue. I couldn't agree more, there is no excuse for not putting in a bit of redundancy. Especially when it could have been so easy. But lets at least keep the facts straight. Which is what my whole point was from the get go. And panzlflyer merely proved my numbers with his own.

Disclaimer: I am only human and therefore reserve the right to be wrong. But I stand by the numbers and past experience. A giant scale airplane is NOT going to pull 20-30 amps.

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02-21-2011 10:35 PM  6 years agoPost 104
basmntdweller

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Indianapolis IN

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Each connector is rated for a max of 3 amps
Most likely true. Schedule 40 PVC pipe is rated to 60psi. I know it can easily withstand 120PSI for years. An elevator may be rated for 2000lbs but I can guarantee it can handle well over that. There is a safety factor engineered into everything. If I had a decent way to test it, I'd venture I could load up one of these connectors to 6 amps and it would be fine all day long.

I'm not saying a little redundancy should have been designed in with extra cabling. I'd use it if it had been delivered factory that way on my 3G and I'll likely do something when I get to installing the GY-750 since it is going on someone else's heli.

I only brought this issue up a few weeks ago as I was curious to see how many would write it off as reasonable since it was a Futaba product but the Align bashers went apeship over the same basic deal on the 3G about this time last year.

Matt


Stupid people have no idea how stupid they are!!!

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02-21-2011 10:40 PM  6 years agoPost 105
Bruce2.5D

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Vancouver, Canada

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Your resistance numbers are about right in theory, but partially miss the point.

(although I'd argue about the rx to fbl jumper, futaba's lead is only 20 or 22 awg and is >6 inches)

First, those numbers are for new, clean connectors. "As flown" systems show higher resistance. Second, many helis are running regulated power at 5 volts, so say 1 volt of jumper-drop gets added to their reg's dropouts.

I agree straight 2s lipos or 6 volts gets around the voltage drop issue for resets, but only for as long as the connectors survive. And it doesn't deal with the loss of torq/speed with the drop in voltage. The connectors are past their rated limits even for the average load, never mind peak load.

Here's the comparison - would you accept a large digital servo with a 26awg (250 heli size) e-flite cable on it? Because that's what you're doing if you run a single 20awg jumper to power 4 strong servos.

Not necc a knock on the system - it just needs some kind of bus or Y-cable rig for use with 700 size helis. It's just not futaba it's half the hobby, the rest of the gear has not kept up with the extreme servos.

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02-22-2011 05:00 AM  6 years agoPost 106
nickmcdonald

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new lenox, il

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Except by the time the load and resistance got anywhere near what your dreaming of, the connector would have completely melted. Just as it would have if you were to pass a 13A load through it. I'm sorry but the part I find funny is that the facts simply don't add up to all the wild accusations running around lately.

How many hear still remember the happy oblivious days when we all flew on 4 and 5 cell Ni-Cd's running through an On-Off switch? The people coming up with this stuff now would probably argue that you couldn't possibly fly a helicopter with such a setup. Yet we did it day in and day out without issue. With much more similar loads than you might think. All that was required was simple maintenance.

I wish I had a better meter to prove that a "Flown" system does not show the kind of degradation your supposing. But testing from servo board to battery plug (3G, R6014 and Arizona regulator in between) still showed up as 0.0 ohms on my meter (+/- 1%). Unfortunately that hundredth decimal place is what I need to prove the facts. But still well below that quoted "0.2 ohms"

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02-22-2011 04:22 PM  6 years agoPost 107
rexxigpilot

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Florida

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Anyone ever hear of a commonly used elctrical component called a capacitor. This is why short spikes or transients don't matter.

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02-22-2011 04:37 PM  6 years agoPost 108
nickmcdonald

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new lenox, il

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Bruce2.5D's argument is that the capacitors don't provide enough protection against those transient spikes.

I'd also point out that the capacitor would be served better if it were attached to the servo.

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02-22-2011 06:34 PM  6 years agoPost 109
Bruce2.5D

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Vancouver, Canada

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>"Except by the time the load and resistance got anywhere near what your dreaming of, the connector would have completely melted."

Not in a short spike, at least not right away. And, in the mean time I actually tested a connector at 10 amps with a steady ohmic load. With a new 20 awg jumper, the resistance was about 0.05 ohms, lower than I thought, but again that's under ideal conditions.

>"How many hear still remember the happy oblivious days when we all flew on 4 and 5 cell Ni-Cd's running through an On-Off switch?"

With analog servos with speeds of about 0.12s/60 deg. That's the point - modern digitals are a different animal. They have a much sharper response to changes in setpoint and load, higher torque, and higher speeds. Plus, the mechanical flybar didn't care about servo response.

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02-22-2011 08:57 PM  6 years agoPost 110
nickmcdonald

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new lenox, il

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Why do you refuse to listen to simple facts. The connector would fail with the numbers you're proposing. And that's given the power system could even sustain such power levels. But it can't, either the voltage loss from cabling, or power loss from load would all but eliminate the chance of power levels getting to that level at the connector. You simply can't have enough load to make a connector fail, the connector staying intact, AND the power system providing enough wattage to cause what your implying. Meaning that all three can't happen at the same time.
With analog servos with speeds of about 0.12s/60 deg. That's the point - modern digitals are a different animal. They have a much sharper response to changes in setpoint and load, higher torque, and higher speeds.
Beg pardon, but digital servos were not created within the last year or so. I flew all digital machines back in 01/02. And before you go argue that digitals weren't as power hungry back then. I pulled around 200mah per flight on a Raptor 50. I do take your point though on the more modern servos and FBL heads. But the differences are not orders of magnitude higher.

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02-22-2011 10:03 PM  6 years agoPost 111
panzlflyer

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Goldsboro,NC,USA

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Mikado advises running 2 connectors, Skookum has a power buss, in fact Art at Skookum was on an internet video saying he saw brownouts on quite a few setups that they tested, owners unaware.
Seems like a a wise thing to at least use 2 power leads imo, but each to his own.

T700,450Pro,Spirit Pro,Beast+, Qav 500,Futaba18SZ

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02-22-2011 10:15 PM  6 years agoPost 112
nickmcdonald

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new lenox, il

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I absolutely agree with using more power connectors. The sum of all the issue's with the systems we run today can cause issues. But it's not from some uber-super servo pulling down 10 amps.

How much do you want to bet that this single wire power issue is what causes 99% of peoples problems with the 3G tail kicking. I started off flying my 700LE 3G without this issue. Then like a brick wall ran into it. Some how I eliminated it and haven't run into it since. Maybe if and when I run into it on my 700E I'll simply try adding additional power connections to the servos via the 3G.

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02-22-2011 10:32 PM  6 years agoPost 113
Bruce2.5D

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Vancouver, Canada

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nickmcdonald: What I was saying in the last post is that I went off and actually ran a single 22 awg jumper at 10 amps continuous for about a minute, and nothing burnt up. The wire/bus carries the heat away but it all gets warm though. The voltage drop, bus to bus, implied a 0.05 ohm resistance.

A connector being run 1-1.5x over it rated limit on average and several times over with frequent spikes, if clean, would probably last quite a while. You can often get away with it. It's just not a good idea.

When a fast digital servo is given a setpoint change of more than a few % of its range, the motor is stalled for a few ms while it accelerates to speed. A stalled motor is a dead short through its windings, so it pulls a lot of amps. And the servos are pulling more amps - now-standard cyclic servos look like the tail servos of a few years ago. Not an order of magnitude more at peak, probably 2x as much. And it probably won't show up on battery drains on an equal machine, because it's the peaks at issue.

And the position changes and rate of change sent to a servo on a FBL system is very different than from a person's thumb. For one thing vibration can be carried through to the servo output via the control loop.

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