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Old Mar 08, 2012, 05:24 PM
BANG IT!!!
DaOldGuy's Avatar
United States, PA, Bellefonte
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Quote:
Originally Posted by SteveTtoooo View Post
Man, you can tell those directions were written in China...

SteveT
hense the more questions. He was honest with me in the email and said the Manual was a tad... thin if you will. I sent some additional questions <sterring engine was one> back but I have not gotten a response yet. He indicated there are other models as well of this, but it may be a bit before they add them.
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Old Mar 08, 2012, 05:31 PM
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jsmith285's Avatar
Fort Wayne
Joined Feb 2009
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Quote:
Originally Posted by heritageflyer View Post
Thanks everyone. This is all clear now. Makes sense. 3S with a BEC Pro it is! (if I ever need a setup like this)......


This discussion was way better than off topic Cats!
But we might be doing something different by then.
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Old Mar 08, 2012, 05:32 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
26,108 Posts
Quote:
Originally Posted by DaOldGuy View Post
hense the more questions. He was honest with me in the email and said the Manual was a tad... thin if you will. I sent some additional questions <sterring engine was one> back but I have not gotten a response yet. He indicated there are other models as well of this, but it may be a bit before they add them.

I tried to call them, but could not find a telephone number. They used to have one on the site, as I know that I talked to him at one time to buy some P.A. wing bags (the only good product P.A. has as far as I am concerned) as they are a P.A. dealer, and that way I didn't have to deal with P.A. directly...

SteveT
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Old Mar 08, 2012, 06:12 PM
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rdsok's Avatar
United States, OK, Norman
Joined Mar 2010
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Originally Posted by heritageflyer View Post
I think the French Connection Cap planes had Canape's.
Good one

... and at least you remembered to put the punch line in... I had planned to say something about enjoying a snack or hor d'oeuvre while at the flying field, just not while flying... and got distracted with work and forgot that part... talk about messing up a joke...

Even worse now... I had to explain it..

Randy
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Old Mar 08, 2012, 06:25 PM
On loan to Texas
Ohio AV8TOR's Avatar
United States, TX, Benbrook
Joined Oct 2005
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Quote:
Originally Posted by DaOldGuy View Post
Could explain why people keep getting more powerful servo? They assume blow back is not enough servo torque, could be a amp bottle neck?

I am trying to get better info on the Power Expander on the Servo Page
http://milehighrc.com/servo.html

Anyone use one of these before?
There is several posts on that over on Flying Giants. I was interested in one strictly from a power management standpoint. Not much good was said but all based on opinions and the fact that it is pretty much a copy of the smart fly.
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Old Mar 08, 2012, 06:29 PM
On loan to Texas
Ohio AV8TOR's Avatar
United States, TX, Benbrook
Joined Oct 2005
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SDHobby is where that Power Box is coming from see here

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Old Mar 08, 2012, 06:29 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
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Quote:
Originally Posted by Ohio AV8TOR View Post
There is several posts on that over on Flying Giants. I was interested in one strictly from a power management standpoint. Not much good was said but all based on opinions and the fact that it is pretty much a copy of the smart fly.
Got a link to that thread?? Heck, it looks decent...wonder what they thought was so bad, other than it is pretty much a copy?

Never mind, I see the link on the box...

And it seems they have another one too...Power box and it has "receiver binding with magic ribbon".... LOL

SteveT
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Last edited by SteveT.; Mar 08, 2012 at 06:40 PM.
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Old Mar 08, 2012, 06:33 PM
On loan to Texas
Ohio AV8TOR's Avatar
United States, TX, Benbrook
Joined Oct 2005
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Quote:
Originally Posted by SteveTtoooo View Post
Got a link to that thread?? Heck, it looks decent...wonder what they thought was so bad, other than it is pretty much a copy?

Thanks

SteveT
http://www.flyinggiants.com/forums/s...ad.php?t=69169

http://www.flyinggiants.com/forums/s...power+expander
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Old Mar 08, 2012, 06:38 PM
Perfect 3pt inverted landing!
teookie's Avatar
USA, AL, Huntsville
Joined Oct 2008
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I've enjoyed this electrical setup discussion.

Something I've been thinking about lately is voltage drop through servo extensions. Let me illustrate w/ an example:

Consider a high torque digital servo hooked up with a 48" extension. This servo can pull 4 amps if it's locked up (worst case scenario). The extension is made with 20 AWG wire. According to Hansen Hobbies Connectors PDF, your typical "20 AWG" servo extension has a resistance of ~.017 ohms/ft.

Calculating the voltage drop in the extension is pretty easy.
V=I*R
V=4amps*(4ft*2*.017) (the "2" is there because the current must flow 48" to the servo, and then 48" back to ground (back to the battery).)
V=.544
Tadaa!

So your servo is seeing half a volt less then your batteries (or regulator) is actually pumping out just due to the wiring. It only gets worse if you add more extensions, use cheap extensions, or Y mutliple servos off of one extension.

If you think .5V is no biggie, consider this: my super vyper was having blow back issues on the ailerons. I had the HS-65's running off the 5.8 or 5.9V from the ESC BEC. Several people recomended I add in a external BEC and set it to at least 6.5. I did and the aileron blow back improved noticably.

Remember though that the voltage only drops this much when the servo is fully loaded and pulling 4 amps. But on the other hand isn't this when you want it getting the most power?

------------------------

What if you had all your servos plugged into your reciever, and were powering the reciever via two 12" extensions. Lets say 5 servos for a total load of 20 amps (worst case scenario). We split this load between the two 12" extensions for 10 amps each. Doing the same calc as above;

V=I*R
V=10*(1ft*2*.017)
V=.34

So in this case the receiver is seeing .34 volts less then the batteries are putting out. The servos are seeing .34V + the loss from their individual extensions less then the batteries are putting out.

---------------------

I guess the point of all this is that it's important to consider the voltage losses in your setup, in addition to potential amp bottlenecks.
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Old Mar 08, 2012, 06:42 PM
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jsmith285's Avatar
Fort Wayne
Joined Feb 2009
4,698 Posts
Data from Scott Servo connector Test

Well, here is the first run of tests on servo connectors. The control test sets the stage on what is expected as normal as we all know it. 3amp current and the connector is just fine, no detectable heat gain felt or measured by laser temp dodad. To start off with there is 15.2mv dropped across a new pair of pins showing there is some voltage loss and some resistance to current under normal conditions. In a perfect or near perfect world we want none of each or at least the same across a piece of wire but since it is a friction fit there is going to be some losses. It's these losses at higher current flow that get us into trouble with brown outs and melted connectors and such.

Test two is much of the same just at a 4amp flow. The voltage drop is a bit higher 20.1mv and after about 3 minutes a little heat can be detected by feel but my laser dodad has a hard time reading the contacts and show little to no rise in temps however, we know there is because of the higher voltage drop.

Test three is at a 6 amp flow, the voltage drop 30.7mv is really coming up now and the pins are quite warm, not so hot you can't touch them but uncomfortable. By this stage it is apparent that the pins are well over their max rating and too much power is being lost across the resistive contact surface, I'm sure the temper in the pins will be lost by this point making the pins loose there gripping strength over time making them even more resistive.

Okay, I'm having fun now just seeing what will happen. At an 8amp flow there is a 42.3mv drop across the pins and are hot enough that I can not hold on to them. At 10 amps my Fluke tops out and the pins are just at the spit sizzle stage so I reset the test with the plastic shell in place and take the Fluke out of the circuit and pour the coals to it. The meter on the adjustable power supply is not accurate enough to use but I know that by adding the last 1157 bulb to the test I was well over the 12 amp range and with in one minute the plastic shell and wire coating began to smoke showing thermal runaway. In the last pic you can see a wiff of smoke off the connector.

Conclusion
Anything over about 5 amps going thru 1 servo connector will become a failure point sooner or later.
We run at least 4 servo connectors on a 50CC plane for power distribution. Might have a lot to do with how Joe flies (Rifle rollers all the way across the field). But minimun of 4 servo connectors for us to power our servos.
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Last edited by jsmith285; Mar 08, 2012 at 06:54 PM.
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Old Mar 08, 2012, 07:11 PM
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tominator06's Avatar
United States, MD, Dundalk
Joined Feb 2009
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I'm running a 3s 1800 rx pack into a bec pro in my 71. Only has 4 985mg's running on it. I had the bec already when I decided to run the extra battery so I just used it. Seems to work fine.
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Old Mar 08, 2012, 07:21 PM
BANG IT!!!
DaOldGuy's Avatar
United States, PA, Bellefonte
Joined Dec 2007
12,041 Posts
Quote:
Originally Posted by Ohio AV8TOR View Post
Not much good was said but all based on opinions and the fact that it is pretty much a copy of the smart fly.
What.... Someone in China making copies... Wait, that is a different thread.

Quote:
Originally Posted by teookie View Post
I've enjoyed this electrical setup discussion.

Something I've been thinking about lately is voltage drop through servo extensions. Let me illustrate w/ an example:

I guess the point of all this is that it's important to consider the voltage losses in your setup, in addition to potential amp bottlenecks.
So are the losses completely in the connectors, or is it the line loss of the 48 inches, which is worst?

Quote:
Originally Posted by jsmith285 View Post
Data from Scott Servo connector Test

At 10 amps my Fluke tops out and the pins are just at the spit sizzle stage so I reset the test with the plastic shell in place and take the Fluke out of the circuit and pour the coals to it.
I get the feeling you enjoy things <controlled enviroment> burning and blowing up... Nicely done!
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Old Mar 08, 2012, 07:25 PM
Once u go yak u never go back
marksextra's Avatar
Erie, PA
Joined Mar 2005
1,290 Posts
Quote:
Originally Posted by jsmith285 View Post
Data from Scott Servo connector Test


Conclusion
Anything over about 5 amps going thru 1 servo connector will become a failure point sooner or later.
We run at least 4 servo connectors on a 50CC plane for power distribution. Might have a lot to do with how Joe flies (Rifle rollers all the way across the field). But minimun of 4 servo connectors for us to power our servos.
Really great information right there. Thank you!
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Old Mar 08, 2012, 07:32 PM
customstandoffs
cmala's Avatar
USA, AL, Madison
Joined Dec 2007
8,547 Posts
Quote:
Originally Posted by tominator06 View Post
I'm running a 3s 1800 rx pack into a bec pro in my 71. Only has 4 985mg's running on it. I had the bec already when I decided to run the extra battery so I just used it. Seems to work fine.
What voltage are you running them at?
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Old Mar 08, 2012, 08:08 PM
Perfect 3pt inverted landing!
teookie's Avatar
USA, AL, Huntsville
Joined Oct 2008
3,089 Posts
Quote:
Originally Posted by DaOldGuy View Post

So are the losses completely in the connectors, or is it the line loss of the 48 inches, which is worst?
I only considered the losses from the wire. Jim's post listed the losses from the connectors at variouse current levels. Just add 'em together for a total.
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