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Evel Knievel's blog
Archive for May, 2009
Posted by Evel Knievel | May 13, 2009 @ 06:48 PM | 4,605 Views
Iím not sure if you remember but I had a problem at SEFF with my foamy that I originally thought was due to a Spectrum ďlock outĒ. The incident confused me because until that point I had had no problems (at SEFF or before). I began to look further into the problem and I also kept your problem with the Slick in mind too. After a sizable amount of reading and analyzing I believe I may know what happened to both my foamy and your Slick.

I believe the problem is the speed controllers internal BEC (Battery Eliminator Circuit) Most ESCís have internal BECís that use a linear regulator. The linear regulator converts the input voltage (say 3s at 11.1V or 4s at 14.8V) to a usable receiver voltage (say 4.8-6.0V). It does this by converting the excess voltage (5-9V) into heat. The linear regulator uses resistance as a simple and cheap way to step down the voltage. The Airboss 80 has a Linear BEC. The Elite series uses a switch mode BEC which I will talk about later. Also, these BECís are rated assuming a 6 volt input source. As the input voltage goes up the BEC cannot convert all of the excess voltage into heat thus the output is reduced. This said it is possible that the internal BEC that is rated for 3A could put out 2A or less on 3s or 4s. The 4 HS-81ís that you were running could easily draw 2A under normal flight conditions (.5A each). All of this being said it is easy to see the problem.

The question still remains: why did the problem not occur earlier? Why was...Continue Reading