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?

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.

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.

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.

That's why we all run castle bec's. No issues.

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.

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).

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.

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.

No, unfortunately. I'm going to gather data from my wife's 1258TG, but that will be another week or 2. If you're in the SoCal OC area, with other than savox, and are willing to participate, I'd be interested in gathering data from your vehicle.

Tekins were well known to be a bit on the weak side for BEC but their latest Gen2 advertises 5.5amps and programmable voltage from 6 to 7.4 volts. Haven't got one yet to try for myself.

Here are a couple examples. 8 amps and 6 amps. Well above most BEC ratings.

And conveniently enough one of many examples of what frequently happens when the often recommended solution goes haywire, not good if running more than 2S.

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.

Certainly. Also a forum tip, click on the little double arrow in a box symbol just after a quoted poster’s name. It will take you to the original post.

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.

Have you compared the size of an external bec and an internal bec? Also have you tried the tests with the switch removed and hard wired? I am not sure but if the bec gets it power directly from the switch and not some sort of internal relay,then a crappy switch could be part of the problem.

The only BECs I've compared are not similar in amperage, so I wouldn't expect them to be similar in size. The Castle BECs are 10A or more whereas the built-in style is 3-5A.

I haven't seen the wiring diagrams, nor have I disassembled any of the ESCs I have that contain BECs, so I can't be completely certain. That being said, I can't image that any of the manufacturers would have all of the amperage running through a switch. General practice for electronics I've seen is to have the switch just complete a circuit to power up the unit.

Thanks for the link and the tip. :-)

I agree with ufo regarding the switch, that has been my experience with several ESCs over the years. The switch is at battery voltage, and low amperage. It is not part of the BEC power path, it just turns the circuit on same as the motor drive portion of the ESC. I ran several KO FET servos for a long time that have a separate power wire going to the battery, I frequently spliced it into the switch for extra error proofing, why I am familiar with the switch voltage. I don't believe the switch is contributing to this issue.

I don't know. For Tekins on 1s applications we often wire the receiver pack into the switch. It works great but that would seem to indicate to me that the BEC power is indeed going through the switch, at least on Tekins.

Good point wingracer, I wasn't thinking of 1S use. But if it works great that suggests the switch isn't causing too much trouble, at least on a Tekin?

Side question if I may, what receiver batt do you and/or most guys use? 2S lipo?

Yep, small 180mah 2s lipo wired into the switch so you just have the one switch to turn everything on/off. From what I hear, this only works on Tekins and one or two other speedos so perhaps the others don't send BEC power through the switch but at least Tekins do.

Oddly enough most of the ESCs I was referring to were the “other” Tekins, 600, 411P &G, 420F. And a Novak T4. Thanks again for the info Sean.

Problem is the ESC (Castle ESC's have a weak BEC) I run savox on all my cars, a Summit with a SC8WP and a 30kg Savox servo, and a Tekin RX with a Savox 1267 in my SCT410 neither need external bec's, caps or anything else. All using Airtronics rx's