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Old Jun 04, 2012, 04:32 PM
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Canton, Michigan USA
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Originally Posted by Ole Joe View Post
The only thing I find at that link are pictures and videos of a guy flying his dead cat! I see no other posts on that page. Sure you got the correct URL?

The headlines of the article read as;

Cats away! Artist turns his dead pet into flying helicopter after it is killed by a car


Read more: http://www.dailymail.co.uk/news/arti...#ixzz1wrGCHVx3
That was funny.
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Old Jun 04, 2012, 04:33 PM
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Originally Posted by ands View Post
twta!
Traveling wave tube amplifiers?
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Old Jun 04, 2012, 04:45 PM
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Lincoln, CA
Joined Oct 2006
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Originally Posted by Prof100 View Post
Go to post 8 of the below thread it explains how linear Becs use a "series resistor" to step down he voltage.
http://www.rcgroups.com/forums/showthread.php?t=1537430
That is routinely how it is handled in linear configuration. I don't know where that guy is coming from at all. Clearly, he is on a rant for some unknown reason. Thanks for the link. I was going to go look for one. But, he just isn't worth the time. The whole point of all of this was to suggest that the original poster get an external sBEC to circumvent his heat problem. Agree?
AJ
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Old Jun 04, 2012, 04:53 PM
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Originally Posted by ajbaker View Post
That is routinely how it is handled in linear configuration. I don't know where that guy is coming from at all. Clearly, he is on a rant for some unknown reason. Thanks for the link. I was going to go look for one. But, he just isn't worth the time. The whole point of all of this was to suggest that the original poster get an external sBEC to circumvent his heat problem. Agree?
AJ
Agreed, though shall not toast one's ESC.
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Old Jun 04, 2012, 04:59 PM
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Quote:
Originally Posted by Prof100 View Post
Oops, it must be my iPad or it's operator. Here is the correct link.

http://www.rcgroups.com/forums/showthread.php?t=1537430
I just read the post you referenced and the analogy of comparing the linear BEC to a continously variable resistor is correct. What's known as the "pass transitor" internal to the linear regulator is NOT a resistor, it's a solid state device which varies it's impedance/resistance and along with a bunch of internnal feedback circuitry in the regulator maintains the output voltage of said regulator fixed. Now AJ seemed to be talking about physical resistors in the ESC when he stated;

"Even then, those resistors (inside the package - you cannot see them without taking off the cover) will still get hot just sitting there."
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Old Jun 04, 2012, 05:04 PM
wottree
United Kingdom, England, Exeter
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Originally Posted by Prof100 View Post
Traveling wave tube amplifiers?
That will do
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Old Jun 04, 2012, 05:10 PM
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Originally Posted by ajbaker View Post
Prof100 described it much simpler than I did.
AJ
Oh, AJ you removed the picture of what one of your students did in 1990 before I could comment. That schematic clearly shows the 2940-5 voltage regulator dropping the input voltage from BAT+ (12V) IN to 5V OUT, no physical series resistors with either the input or output of the regulator. How did that picture explain what you were talking about concerning the resistors inside the ESC?
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Old Jun 04, 2012, 05:11 PM
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Lincoln, CA
Joined Oct 2006
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How does that crow taste?

Quote:
Originally Posted by Ole Joe View Post
Explaining basic electronics to AJ is like shoveling sand against the tide. I can assure you and everyone else who follows this forum that ESC's with linear BEC's do not use resistors to drop the voltage from 12V to 5V. AJ, with 15 years in teaching both basic and advanced electronics should be the first to know that would be a ridiculous way of dropping and regulating the voltage to the receiver and servos.
I would think that after reading Prof100's link that an apology would be in order.
AJ
.
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Old Jun 04, 2012, 05:31 PM
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Originally Posted by ajbaker View Post
I would think that after reading Prof100's link that an apology would be in order.
AJ
.
Well obviously AJ you DIDN'T read the link that Prof100's referred too. The person who posted that link states the following;

"A linear BEC is on all of the time and to reduce 42 volts to 5 volts it has to drop the excess 37 volts across a series resistor (which is actually a variable impedance transistor)"

He clearly states that the resistor he refers too is a TRANSISTOR, not a resistor. That transistor is internal to the 3 terminal regulator and is not a physical resistor like you stated in your post. You can't take the cover off an ESC and see physical resistors like you suggest.

You should be the one apologizing for your erroneous post.
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Old Jun 04, 2012, 05:34 PM
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Can't we all just get along??...
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Old Jun 04, 2012, 05:37 PM
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Lincoln, CA
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Originally Posted by bigdogg1 View Post
Sounds good, but in absence of a watt meter ESC seems quite warm after a fairly short WOT test run, Maybe a couple of minutes
Should it be too hot to touch or not
I think the above post has been adequately addressed. The suggestion was THIS. End of discussion.
AJ
As long as I have drifted off topic, I have a question. The Sky Surfer stalls fairly easily. I just built a Lazy Bee (48" WS) and I cannot make it stall no matter what I do. Can someone explain why that is (aerodynamically)? My guess is that the wing on the LB is so large and close coupled to the empennage that a stall (conventional-hold full up elevator while at idle) just won't happen. Any of you A&P guys (or ??) have a simple explanation. OR ..... Here is a video of my plane:
Lazy Bee 5-30-12 Maiden Part I.mov (2 min 17 sec)
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Old Jun 04, 2012, 05:43 PM
Better then Sliced Bread!
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I do not think the SS stalls easily, it can stall but it's not like stalling a P51 :P
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Old Jun 04, 2012, 05:54 PM
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Originally Posted by NorCalMatCat View Post
I do not think the SS stalls easily, it can stall but it's not like stalling a P51 :P
I need to explain "easily". I mean by using "my" test stall - which is holding full up elevator while the motor is off (at 4-5 mistakes high). The SkyS will literally fall out of the sky every time when I do that. The LB will not stall at all. I am just curious what prevents the stall in case I can apply it to other scratch built airplanes.
BTW-I am building a House of Balsa P-51 - So..... don't scare me with that example.
AJ
P.S. Sorry guys. I will get back on topic......
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Old Jun 04, 2012, 05:57 PM
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Originally Posted by JoshB View Post
Can't we all just get along??...
I agree. His posts contribute absolutely NOTHING. Newbies always try to showcase their lack of experience or knowledge. I haven't blocked anyone from this thread yet. Maybe I need to start with him.
AJ
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Old Jun 04, 2012, 06:04 PM
Row 0, Seat A
G550Ted's Avatar
Savannah, GA
Joined Jan 2008
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I don't agree

Quote:
Originally Posted by Prof100 View Post
Agreed, though shall not toast one's ESC.
With aj's conclusion that what he needs is "an external sBEC to circumvent his heat problem."

I DO agree with your statement that it should not toast his ESC.

There should never be an issue of two different 30a ESCs getting "smoking hot" running a stock motor in this model. Something else is going on and I seriously doubt it has anything to do with the BEC portion of those ESCs. 30a ESCs most always have a BEC of at least 2a and often 3a rating/capability which won't overheat with 4 servos even on a 4 cell battery unless at least a couple of the servos are stalled. If all of the controls are working OK then all of the discussions to date are not applicable and using an external BEC (or UBEC or whatever one wants to call it) will not be a cure to his problem.

As NorCalMatCat pointed out, at max power the stock motor draw is about 17 amps. Even on the bench for a couple of minutes I would not expect a capable 30a ESC to overheat. First thing to do is to check the load with a watt meter. Also feel the motor and bullet connectors to see if any or all are getting hot. Does the motor make any strange sounds? What size prop are you running? Does he have another model that he could test his ESC with? Maybe he really is just unlucky and got two bad ESCs.

Bottom line is he needs to do more troubleshooting, and if he can't isolate the problem let us or others know of all the particulars to see if we can offer a possible solution. A UBEC is most likely way down the list as a cure.

Ted
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