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BECs weak in general?
Saw an interesting occurrence today at the track. A person with a B4.1 asked me for some help because his car wasn't running properly (brown-outs). He recently changed to an MT-4 radio, so we could see what voltage the receiver is detecting. Castle Sidewinder SCT and 3800kv motor, 35C battery at 8V, no movement of any kind, and the BEC shows 4V. Wiggle the steering (Savox 1258) and the voltage drops to 2 and stays. Changed batteries to a 70C with the same scenario, and the BEC would drop to the 3 range, then return. Next, no steering movement, BEC at 4V. Blip the throttle, and the BEC voltage drops and stays at 2 again. With all of the issues people are reporting lately with brown-outs, is it possible that the built-in BECs are all just barely/aren't enough to do the job?
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Umm, with that servo, yeah not much surprise. Probably fine with most other brands and models of servos, maybe even some other models of that brand.
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Yep, savox are known for this. I have a 1257 that does the same thing. Got a receiver cap and the problem went away. Might be better to have a stand alone BEC and run straight off the battery.
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basically? yes
Savox didn't help but we are facing more and more problems due to hungry servos |
I don't see how it's the servo's fault when just pulling the trigger causes the voltage drop while holding the car up the bench. There was no steering input whatsoever.
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That's why we all run castle bec's. No issues.
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Originally Posted by ufoDziner
(Post 12167463)
I don't see how it's the servo's fault when just pulling the trigger causes the voltage drop while holding the car up the bench. There was no steering input whatsoever.
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Originally Posted by wingracer
(Post 12167608)
The servo draws a lot of power just sitting and holding center. If it is drawing enough to max out the BEC, hitting the gas is just going to draw it down all the more. This is a VERY well known and often discussed problem with Savox servos. Fortunately, some ESC manufacturers are starting to address it by building in more powerful BECs but only a few.
http://i514.photobucket.com/albums/t...rrent_Draw.png |
Interesting. Got any graphs of non Savox servos?
You are right that most BECs are pretty weak. There is a reason for that, they never needed to be strong before. Newer servos are pushing them to the limit. |
Originally Posted by wingracer
(Post 12167608)
Fortunately, some ESC manufacturers are starting to address it by building in more powerful BECs but only a few.
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Originally Posted by wingracer
(Post 12167692)
Interesting. Got any graphs of non Savox servos?
You are right that most BECs are pretty weak. There is a reason for that, they never needed to be strong before. Newer servos are pushing them to the limit. |
Originally Posted by ufoDziner
(Post 12167694)
I see Novak is advertising a 5A BEC in the Pulse. Who else is offering something larger than a 3A built-in BEC? Has anyone measured to see if what is advertised is actually what's being delivered? I would really like to gather some data from people with any ESC, spektrum radios and various servos. So, if anyone is in the SoCal OC area, and is willing to participate, send me a PM.
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Originally Posted by ufoDziner
(Post 12167638)
My Savox doesn't draw hardly any power while idle, and I find what you claim very hard to believe. This is a very speculated problem IMO. People arbitrarily blame the servo when in fact it can be the BEC, or receiver that is the weak point. Other than myself, I have yet to see any data to back up what people (including yourself) claim is a servo issue. I am not using the same servo as he is, but am going to gather data on the same model the next time my wife drives her truck. The following is a graph of my Savox 2271SG amp draw (which I've posted a million times trying to get REAL data from anyone else blaming servos).
....
Originally Posted by kufman
(Post 10503487)
They aren't inefficient, they just draw power in a very nasty way. They have a very high starting current and they draw their current in a very spiky fashion. I put my 1256 on a o-scope and work and compared it to other servos. My guess is that they don't put any kind of filtering in the servo and other companies do. When I tested the 1256 I was seeing peak currents that were around 8A. The bottle neck is the system is the wire that connects the ESC to the receiver. With high current spikes you also gets large voltage drops due to series resistance. This is further aggravated by today's modern receivers which do not have internal BEC circuits and the voltage regulators that are used to power the processor do not have much of a hold up cap on them.
Originally Posted by aradaiel
(Post 10512084)
I just went though this with my savox stuff. They perform well, they just pull a ton of power.
At stall torque savox pull 6a or so, hitec pulls about 2-4a. I tried wiring the servo power directly to the lipo and bypassing the bec of the ESC. It works except my servo is twitching under braking to the point the car is undrivable if I have to use brakes. Here's the idea of powering a 7.2v servo with the battery: http://www.shopatron.com/products/pr...6514/166.0.1.1 I had to go back to hitec.
Originally Posted by kufman
(Post 11378769)
Sounds like your Castle BEC failed in a nice fashion. Mine put 16V into the receiver. :flaming:
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Originally Posted by Dave H
(Post 12168265)
Here are a couple examples. 8 amps and 6 amps. Well above most BEC ratings.
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Originally Posted by ufoDziner
(Post 12168334)
Thanks for the quotes. Could you kindly post the thread links so I can read further? This is the first I've read of anyone testing with equipment besides myself. Thanks.
Post 15 and 29 I believe from this thread: http://www.rctech.net/forum/electric...ly+Savox+servo I'm sure I could find more, if I have a chance I'll snoop around some more. |
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