Power distribution or not

[Joel]

Hi,

As I finish up my DG1000 ( in sailplane build thread ) I'm getting to where I need to decide how to hook it all up. Simplest route is to hook all the servos direct to the receiver and use a single big battery. Next level is to hook it all up to the receiver with redundant batteries. Of course it goes on and on from there. I'm thinking I will need the weight of good ole NiCds in the nose for balance, so I don't feel too compelled to get something for say dual LiPos and VRs for the receiver and servos. The sailplane has all digital servos ranging from an HS-7955 to HS-5065s. When I think about the power, most of it is the HS-5125s in the wings, HS-7975 and HS-7985 for the rudder and elevator. The rest kind of sit in the same position most of the flight. The two biggest servos for the retract and SLS arm are adjusted to where they have no buzz in either position, so shouldn't be much draw other than when moving. My thinking is the ideal setup would be something that takes the dual pack input with isolation between packs ( don't know if it really needs active balancing ). The receiver already has a regulator in it and because my plan so far is for dual five cell nicads, don't think I need yet another. I do think busing the power strait from the batteries to the servos makes sense so it doesn't all need to go through the receiver. My other scale sailplanes were much simpler and I really didn't worry too much about power. The DG is big ( to me ) and heavy and has much more crammed into it than anything I've had before. Any feedback appreciated.

Thanks

Joel

[Len]

And so it begins,
Be ready for different opinions on this subject. With a plane that big and that expensive, most of us will run three batteries. Two for the flight pack and one for the retract. You could and should run the up and go servo power from the retract battery too. The reason has been talked about for years and its always good to refresh this subject.
The retract can and will jamb. Even if its from a stick that gets kicked up on takeoff, you never know its even happening until it drained your flight pack and the plane is diving at the ground. A well known and highly respected pilot from California had this happen to him. I dont thing he lost the plane, but it was close. You never can be certain the gear is up and locked, without straining the servo, so a separate battery there is a must. There is a wire diagram on the main website that shows how to wire that into the circuit.
As for the flight packs, On the real big stuff, 6+ meters. I run Power box systems because of simplicity. It allows for programing and controlling servos without any problems, regulates voltage and other benefits when running 20 servos. The problem is they are way expensive, but as an alternative Smart Fly is very good too.

If you are flying JR equipment, then you can run the Power Safe receivers, they are set up for two power inputs. If you are flying Futaba, it doesn't matter, its gonna crash anyway...............I AM KIDDING..... Futaba is fine,( for park flyers ) JUST KIDDING AGAIN, lets not start a war. I have both. ( wanna buy a Futaba ) , Oh come on, somebody stop me.. lol

Anyway, You certainly want two flight packs, and one for the gear/SLS extension motor.

Hope this makes you laugh and answers some questions.

There are also some devices that Emco-tec makes that will cut off the power to a servo if it detects a stall. I have them on retracts now and am very happy with them.


LEN

[yyz]

Joel,

You have a beautiful sailplane and it makes sense to spend some time now, like you're doing, to understand what your options are. I made a "power" mistake last year and it cost me a glider.

Minimally, I would have two separate and large battery packs, each going into a separate input on your receiver. That's one level of protection: a single battery failure won't kill you. Test this on the ground to make sure the receiver is doing the right thing if you lose one of those batteries.

Second, anything that can jam (tow release, retract, SLS extract/retract) and possibly drain a battery goes on a separate battery. I typically gang the tow release and retract servo on a separate battery pack. The tow plane can release and you can land gear-up if necessary. There's another level of protection. There is a wiring diagram floating around for this. I can scan it and post if if you can't find it.

I've had good luck with the two-cell LiFe packs, using three separate packs as described above. With any reasonably-sized plane, you can pretty much fly all day without recharging.

The power systems are nice if you need to gang multiple servos driving the same or matching surface (like Len's and Dennis' planes where you need multiple servos to drive a surface). From what I've read of your build, I don't think that's an issue for you.

Hope that helps,

Mike

[Joel]

So it sounds like a simple approach would work fine for me. My initial thought with the retract and the SLS was that they tend to always buzz being a constant drain, that I was able to address easy enough. Jams are another thing. How much faith do you have in the new servos and the OCP protection they have. I played with this a bit and it seems to work quite well on the bench. Servo hit its limit and quit driving. You can go the other way again just fine and if the jam were to go away ( twig fell out ) all operates normally again. Even though the sailplane is large, with scale interior there is not a whole lot of room for stuff. My thought is to use two large packs with isolation for the receiver, connect the SLS and retract servo to one of those. In this case if a servo jams and does draw a pack down, there is still the other. I do like some of the power distribution devices because they do as mentioned, simplify some things, the other hand is that if you don't have a real need to use one, they are another possible point of failure. Hopefully this week I can set the sailplane up and see what it needs to balance, this will help me finalize some cable management items.

As far as JR vs Futaba, My MC4000 is the best radio I have owned, I will probably put my 12Z in the DG. For that I'm just deciding between 50MHz and 2.4GHz. I notice the TX sucks the battery down much faster on 2.4.

Thanks

Joel

[louierc]

Joel - Just finishing up my 1/3 Ventus for a maiden at Cumberland. I used 2x 5 cell 3300 mAh NiMH packs on a JR Powersafe RX. Another feature that may not have been mentioned is that the Powersafe RX has a fail-on switch. It must be closed to turn the RX off. A third pack will be used to power the retract. I did not put the tow release on the retract battery, I can't see how it can get overloaded (I will rethink that). Use an in-line voltage and current meter on the battery to check the current draw of the whole plane, as well as the things like the retract servo, and make sure the travels are set so as to avoid stalled servos / high current endpoints.

I would avoid 50 MHz - while it would have been OK years ago (I started RC in the 70's on the Ham band) I would never trust it now, especially on an expensive sailplane.

Good luck ! Louie

[louierc]

LEN - speaking of JR ( and not Futaba ) are you using DSM2 or DSMX ? Several in my flying group have changed everything over to DSMX, but I'm not sure this is an advantage unless you are at a large meet. Comments?

Louie

[Joel]

Hi

I still have some vintage RC equipment I use on the old 53MHz frequencies, still not an issue where I'm am located. I fly all my helis on 50MHz. Have you had specific issues with 50? I though it was still in the band plan for RC use where as 53 I think no longer is. For 53 I just make sure there are no repeaters near the frequencies I use.

Joel

I would avoid 50 MHz - while it would have been OK years ago (I started RC in the 70's on the Ham band) I would never trust it now, especially on an expensive sailplane.

Good luck ! Louie

[Len]

Just kidding about the JR/Futaba thing. I actually do have both, I grew up ( thats debatable ) flying with Futaba, I switched to JR because of 2 reasons.
1) they have far superior Sailplane programing
2) If they are going to spend many many THOUSANDS of dollars hosting an event specifically for Aerotowing, and have been for 10 years, I owe it to them to fly their stuff. Thats just me.

As for all the other stuff, better reception, blah, blah , blah, its all whatever you want to believe. PR departments at work.

Louie,
I talked with Peter Goldsmith last year when it first came out, he stated that you current system is fine, the advantage of the X system is when you go to a huge event like Noll, or those other things. ( I don't know the names because I don't go to those events)
IF there are 40 radios on, it would be an advantage. Nothing we do to would have those numbers YET

That being said, whenever I get new receivers, I do get the x, why not? Also, Please read the Power Safe booklet, you must unplug the batteries when you store the plane. There is a slight draw at all times.

What other servos are you talking about. I haven't followed the servo game lately. Let me know and we'll see what we can dig up.

Joel.
I'm not an expert on batteries, but I think the setup you are talking about is not the best. Here's why, even though you are using two packs, they are being consumed equally. Not one at a time. That only means a stuck servo will give you twice as long a flight before it plows your 6+ THOUSAND dollar ( US Currency ) sexy glass slipper into the earth.
The idea of the separate pack only on for retract and maybe something else, is that it is in NO way connected to the receiver packs.

Good topic though, thanks for the interesting conversation.

LEN

[louierc]

A couple of comments - True - two batteries are discharged at the same rate with the dual battery scheme with a Powersafe RX, and you can run both batteries down. However it DOES account for a failed battery, bad cell, shorted pack, etc, and has isolation to allow the RX to continue to run off the remaining battery.

Another scheme that I have in my DG-600 and some large scale planes is dual RXs and dual batteries. The control surfaces are split between the two RXs (which are both bound to the same TX) so that a complete failure of one system hopefully leaves you with some control to get your plane down - one aileron and one side of the elevator. Better odds.

If you look at the most common RC control failure that results in a crash, it is the RX battery or the RX switch - by far.

Louie

[Joel]

Hi Len,

In the setup I'm thinking of, you are correct, both are being used equally until..... The SLS and retract are only connected to the one battery. If it gets sucked down the SLS and/or retract will not draw from the remaining battery. Only the receiver and the rest of the servos run off the remaining battery. Now, if the SLS and/or retract fail and suck a battery down AND the other pack fails you are in trouble, but then you can take redundancy too far. I agree with Louie that pack failures and switch failures are the most common. I think in the 38 years I have been doing this I have had one of each. In recent years ( 15 or so ) I have probably been more aware of the condition of my equipment. I generally quit using my batteries for critical use when they are at 80% of new performance ( the one battery failure I had was in a heli, expensive lesson ). I'm still down the investigation path so no choice has been made yet.

Joel