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Old Oct 10, 2012, 08:54 PM
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Joined Dec 2006
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Originally Posted by Prof100 View Post
A 4S with a linear BEC is a recipe for disaster simply because of the voltage step-down to servo voltage generates far too much heat which can and will shut down the ESC. A 3S with 4 analog servos (with no binding) is the maximum or 3 digital servos . Six servos ona linear internal BEC is insanity and suggesting it is OK is absurd.
A good point I hadn't thought of. A linear BEC with a 3s (11.1V) battery that puts out 5V to its servos at 3A, is dissipating 18.1 Watts into heat by itself. With a 4s (14.8V) battery the BEC alone is dissipating 29.4 Watts. That's a lot, and would be added to the heat generated by the ESC itself.

Of course, you'd still have to stall all six servos simultaneously to achieve that 3A draw, if these 17g servos draw as much as the larger, higher-torque 37g and 45g Futaba servos in the other thread.

Prof, you've had extensive experience with servos, ESCs etc. Could this BEC-dissipation problem be why the builders of the linear-BEC 40A ESC in the SSS manual rated it for only 4 servos and a 3s battery, while they rated the switched-BEC 40A one for 5 servos and up to a 4s battery?

And, do you have any educated guesses about how much current these 17g servos in the SSS might draw under "normal" loads the SSS may put on them? I've been unable to find any documentation - that older thread where the guys tested their Futaba servos, is the closest I could find, and they didn't test "normal" loads.
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Last edited by Little-Acorn; Oct 12, 2012 at 02:15 PM.
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