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Post by ginginho on Apr 20, 2009 10:07:02 GMT 1
Thanks chaps for more interesting info. It's a shame the owner of the link in the original post hasn't tested some more servos, just so we have some idea of what we might have/be buying. Without a scope it makes it very much hit and miss as to whether a BEC will struggle with the selected servos, if not one of those tested.
When I converted my cub I read through quite a few forums regarding this and Specktrum which (I'm glad to say) helped me to decide on an ESC with a 3A switched mode BEC. I've not experienced a brown out with 4 servos on this, but I have no idea what sort of draw the servos I fitted pull, maybe a 2A wouldn't have been enough.
For any additions to my hanger, I certainly will consider using a UBEC, for peace of mind if nothing else. I see a lot of installations with UBEC use a seperate battery pack for powering these, but I'm wondering whether it could be powered from the main battery (saving weight) using a Y cable of some description. I'd assume a 3S or 4S pack will still be able to power the UBEC, even if it hit LVC (which I wouldn't do!), so can't really see any advantage in a second pack. Am I missing something with this thought process?
One think that makes me wonder is in a ARTF or RR kit, how power hungry are the servos likely to be..I know I'd be pretty upset if I had a new model that crashed due to a brown out. I doubt many lower cost model manufacturers (such as chinese imports) will supply quality electrics after taking into account these things. I'm more likely to expect the cheapest ESC and servos, which may be a recipe for disaster if fitted with a (leccy sensitive) spektrum Rx. I dont' ever recall seeing one of these sort of kits (in a similar size to the SC) with a UBEC...
Cause for much thought.....
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Post by flydiver on Apr 20, 2009 16:42:28 GMT 1
For park size planes a UBEC is grafted in and uses the main power battery. All you are doing in taking the load off the internal BEC in the ESC (disconnecting that red wire).
Adding a separate battery is possible but increases weight fast. Most folks do this when they get to larger planes. At that point you may be using 4S->MoreS batteries, large ESC to handle it, and they don't come with a BEC anyway.
I think you are right about some/most cheap planes with 4 servos. The one's I've seen are pretty much borderline to worse. Unfortunately some of the PZ planes not designed for Spectrum may come this way and I'm starting to have my suspicions about a few of those that put in 4 servos including a digital.
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Post by flydiver on Apr 21, 2009 3:01:54 GMT 1
Buddy at the field broke a wing servo in his Corsair. He went home and replace both of them. When he got back there was a BIG stir. The LHS sold him 2 digital servos so now he had 4 digital servos. We had just been discussing the issue of 4 servos on 3S and the need for an UBEC. Of course he wanted to fly his plane-it was fixed. Now he was getting info thrown at him from all sides whether he could do so safely. The most 'experienced' (best flier, most years in the sport) advised him he could do so as long as he was easy on the throttle. Those of you who have actually read some of the background data know this is incorrect-you stress the BEC more with part throttle. We DID hook it up to a wattmeter, ran it at full and part throttle while working the hell out of the servos. No problem. So he flew it successfully. So, I'm sending him this same info to get him up to speed. All this was a completely new and undesirable concept to deal with all of a sudden. More crap, more expense, more complexity.... I decide to go look up his eFlite ESC (30A) to get the real specs. I do that kind of thing. Turns out it is a switch-mode BEC and is claimed to be able to handle up to 4 digital servos. Very interesting. Read about it. www.parkzone.com/Products/Default.aspx?ProdID=EFLA1030 |
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Post by paulharris on Apr 21, 2009 3:53:39 GMT 1
Of note and addition to this topic. I recently inquired to Castle Creations about servo load on the BEC on one of their ESCs. I got the following reply from one of their specialists:
"If you wanted to test if it would handle it for SURE, unplug your motor, turn on your radio, plug in a freshly charged 3s lipo, and then exercise all servos for 20-30 seconds and see if the servos slow to a crawl or stop momentarily. That test works for any regulator on any ESC."
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Post by ginginho on Apr 21, 2009 11:24:46 GMT 1
[Snipped] I decide to go look up his eFlite ESC (30A) to get the real specs. I do that kind of thing. Turns out it is a switch-mode BEC and is claimed to be able to handle up to 4 digital servos. Very interesting. Read about it. www.parkzone.com/Products/Default.aspx?ProdID=EFLA1030Interesting reading indeed. That would seem to be a pretty good quality ESC, although I'd be a little concerned with the statement of "700mAh continuous current ". I guess the servos they tested with are sub-micro-sized servos ( 9 gramme??) which draw a small current, certainly I wouldn't expect that to work with 4 of the higher powered servos listed in the scoped tests. I guess you get what you pay for, but then on the flip side, are other ESC's capable of similiar, when using similar servos? Although I don't have any experience of digital servos, the 4 I have are obviously OK with a 3A switched BEC, as mentioned previously. It's certainly something that all flyers should be aware of, at minimum. |
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Post by flydiver on Apr 21, 2009 16:46:57 GMT 1
PZ is somewhat specific in the Tech Notes on that link. They can't test all the servos out the, people will always buy others.
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Post by Dillzio on Sept 13, 2009 8:14:02 GMT 1
Thanks for the tip. That sounds just like the kind of mistake a noob like me would make.
I'll be sure to get a separate BEC when I finally upgrade.
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Post by hrtpaul on Oct 7, 2009 13:28:11 GMT 1
So I guess from what I've read, I could be a little marginal with this 30A Brushed ESC www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=6468 and 2 HXT900 servos in my beasty. Now where the hell am I gonna stick a UBEC ?  It's already crowded what with an AR6000 Rx, 3S 2200mAh lipo and the above ESC. Thanks for the heads up though. Very interesting, especially for the noobs among us (me included) |
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Post by Dillzio on Oct 7, 2009 14:48:40 GMT 1
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Post by flydiver on Oct 7, 2009 16:31:34 GMT 1
If you only have the 2 servos on 3S you are probably OK. You could also just switch out to Hitec-55's, more efficient.
Crude method of checking. Lock the plane down-no wing needed. Put in a full battery. Fire it up ~ 1/4 throttle. Work the bejeezus out of the stick for FULL control throws for 2 minutes. Work that sucka. If you get control failure, sagging/laging controls or the ESC gets real hot you have a problem.
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Post by patmatgal on Oct 7, 2009 17:39:10 GMT 1
hrtpaul
You could try attaching the AR6000 to the front wall of the tail section, behind the servo pockets. I tried this & like it, it gets a rats nest of wires out of the compartment under the wing (really cleaned it up) and being able easily check that the bind is good puts my mind at ease.
PS That 3 holed piece of foam came off in flight so I had to tape it down.
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Post by hrtpaul on Oct 8, 2009 9:16:03 GMT 1
It just so happens I found exactly this UBEC in a $10 Minibee flying wing as an extra thrown in. Got to love that. Wiring it in as we speak. All I need now is some no wind days Thanks guys for the tips. Once I get it in, I think I'll try flydiver's test anyway just to be sure. Cheers Paul |
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Post by ginginho on Oct 8, 2009 9:22:51 GMT 1
It just so happens I found exactly this UBEC in a $10 Minibee flying wing as an extra thrown in. Got to love that. Wiring it in as we speak. All I need now is some no wind days Thanks guys for the tips. Once I get it in, I think I'll try flydiver's test anyway just to be sure. Cheers Paul Paul, when wiring this up, remember to push the middle pin out of the connector from the ESC that plugs into the Rx and tape it out of the way. Otherwise the built in BEC in the ESC will be fighting the UBEC to supply power to the Rx. Things go a bit wierd if this is the case. Best to push the pin out rather than cut it off, it can then be re-used in the future. |
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Post by hrtpaul on Oct 8, 2009 10:58:34 GMT 1
Well what a pain in the ar$e. Oops. Read your reply a little too late ginginho I cut the wire in the middle so I can solder it back together. Anyways. I installed this as per instructions. Cut the red (middle) wire, plugged the UBEC (with 1 red and 1 black wire) into the batt/bind slot on the Rx. I plugged the ESC (w/cut red wire) into the throttle slot on the Rx. Tidied the wiring and thought I'd give it a go. I turned the Tx on and connected my battery. As soon as I connected the battery the motor went to full throttle and scared the $hit outta me. Busted the prop  The throttle on the stick was at idle. WTF is going on? Hopefully someone a bit smarter than me can figure this out GRRRRR. Also. Should I have the jumper on the UBEC set to 5 or 6 volts? Thanks again guys |
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Post by Dillzio on Oct 8, 2009 13:44:18 GMT 1
Can you try re-binding it? Or resetting it? Might be a good idea to disconnect the motor or take the prop off until this is resolved, but you've probably worked that out for yourself. ;D
Might be worth making sure the UBEC socket isn't interacting with the bind pin too.
You should set the UBEC to the voltage that most closely matches the specifications of the receiver, if they're both within range then it really doesn't matter, although a higher voltage will make your servos travel a bit more quickly and have a little more pull.
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It's already crowded what with an AR6000 Rx, 3S 2200mAh lipo and the above ESC. Thanks for the heads up though. Very interesting, especially for the noobs among us (me included) 
The throttle on the stick was at idle. WTF is going on? Hopefully someone a bit smarter than me can figure this out GRRRRR. Also. Should I have the jumper on the UBEC set to 5 or 6 volts? Thanks again guys