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Old Sep 23, 2009, 08:59 AM
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rcmorrow's Avatar
Stamford, CT
Joined Jan 2005
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Two questions for a DG-600 Build

I am working on installing equipment in a 4/4.8m DG-600 from H model, available from Icare. It is a wonderful kit and beautifully made.

I worked on the retract landing gear last night and want to have the egar servo have its own power source. I tried having the signal wire go directly to the reciever and then use power from the battery for the + and - leads (red and brown). The servo is erratic and unrelkiable whith this wiring. I am missing something here, any suggestions?

Also, gear doors and a mechanism for pulling them up when the gear retracts....suggestions ???

Thanks for the help !

Bob
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Old Sep 23, 2009, 12:08 PM
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Chandler, Az.
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Servo jitters?

Bob:

Don't know about the gear doors, but the servo power and signal lines must have a common ground referance (grounds connected together) so the signal input is "clean".

Bob
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Old Sep 23, 2009, 01:06 PM
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Thanks,

Both questions solved now, many thanks to all who helped.

Bob
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Old Sep 23, 2009, 05:24 PM
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Canada, ON, Toronto
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Inquiring minds want to know the whole solution (a bit more than post #2, please), as I was about to ask the same question myself.

Dave Smith
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Old Sep 23, 2009, 06:41 PM
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United States, FL, Jacksonville
Joined Sep 2005
639 Posts
Guys
John Derstine had a lot of great building tips that were just found by someone on RC Groups. I made a copy of the url..

Check this out.. Has a wiring diagram as well

http://web.archive.org/web/200407011...tractpower.htm

Hope it helps.

If you need more tech Tips go here
http://web.archive.org/web/200406031...g.net/tips.htm

Good luck
Bill
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Old Sep 23, 2009, 06:55 PM
No substitute for aspect ratio
SPasierb's Avatar
Norwalk, CT aka the Nutmeg State -- I just can't seem to find any %$#@! nutmeg here?
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Here's the diagram I provided to Bob. I picked it up a few years ago, I believe right here?

Steve
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Old Sep 23, 2009, 09:27 PM
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Forest Hill, Qld 'Stralia
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I like that idea of a seperate battery in case the retract stalls the servo, what size would you suggest to use, just 600 mah?
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Old Sep 23, 2009, 10:04 PM
No substitute for aspect ratio
SPasierb's Avatar
Norwalk, CT aka the Nutmeg State -- I just can't seem to find any %$#@! nutmeg here?
Joined Nov 2003
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Depends on the size of the plane and if you need some weight in the front -- better batteries than lead. My current set-up is 1700 mAh.
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Old Sep 23, 2009, 10:55 PM
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Nanuet, NY
Joined Dec 2001
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Follow-up question

Could you protect your rx battery from a stalled landing gear servo by putting an appropriately rated fast-acting fuse in the + line from the rx to landing gear servo? Would this not do away with an additional battery worry and achieve the same result?

BobB
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Old Sep 24, 2009, 07:39 AM
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Toledo, OH
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this seems to be an idea that comes up regularly about a seperate battery for the LG servo. what causes this servo to stall?
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Old Sep 24, 2009, 08:13 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
I personally would not use a fast acting fuse as the potential for falsly blowing the fuse is great. There are two main failures for the retract servo. 1), if it is an analog servo, you'll likely strip the gears and 2). if it's a digital, you'll likely burn out the power amp inside the servo.

The problem with most retracts is the combination of the friction-based actuation mechanism and the chosen gear door solution.

Most "Hock/Fema" style retracts use a pin that slides in a slot within the actuating mechanism - something like a pin/slot based lever. This mechanism has a fair amount of friction that needs to be overcome at the full in and full out extremes as well as when the retract is being pulled in IF the counter-balancing spring is not well selected. It is better if this linkage is lubricated in order to reduce the friction. The downside of lubrication is the collection of dirt within the lubricant that further adds to the friction if not monitored and cleaned. The act of landing and taking off causes debris to be pulled into the fuse through the retract doors when the retract is down. This has a cumulative effect for increased debris over time.

Combine this with the standard method of gear door attachment, opening and closing (the retract pushes open the doors and rubber bands pull them closed) and you present large and sometimes variable forces that the servo needs to overcome to consistently operate the retract.

If this setup is not done with due diligence to reducing the friction forces involved as well as ensuring that absolutely nothing can catch on some other part of the setup, it is quite feasible to cause everything to lock up and jam.

The key is that the retract mechanism is different than almost ALL other servo driven items in a sailplane because of the friction involved. It therefore represents the greatest risk of stalling a servo. If it is a digital, you could be talking a couple amps being drawn from the pack during the stall. If left to it's own devices, the result can be catestrophic if you are using the receiver power source.

My earlier comment about a fuse stands in that it is quite feasible to see varying loads on the retract servo over time - up to the full stall current of the servo if the retract mechanism is not regularly maintained. Placing a fast acting fuse in the cct could cause premature failure of the retract.

On the other hand however, it might very well be a useful approach as an early warning indicator of when maintenance is required on the retract mechanism (i.e., the forces on the servo have increased). I personally choose the additional pack with common ground.

Tony
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Old Sep 24, 2009, 10:53 AM
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Nanuet, NY
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Tony,

Thanks very much for the very informative and thorough reply to my question. You have certainly covered all of the bases and have given me more pros and cons to ponder.

Thanks,
BobB
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Old Sep 24, 2009, 01:27 PM
bie
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Germany
Joined Oct 2004
789 Posts
Hi there,

over here in Germany we have a lot of Scale/Semi-scale-aerotowing-action and most of the gliders have a retract (if the full-scale has one as well).

But I donít know anybody who uses a second battery-pack just for the retract (of course there may be some guys who do it, that I donít know of) in their gliders. Seems to me, that itís an american issue ...

To tell not only from my limited personal experience I can say, that I observe closely the german messageboard RC-Network and participate on an almost daily basis there from day 1 in 2002 especially in the glider/scale-glider-section and I canít recall any substantial discussion on this topic.

Tonys observations are very accurate and true without doubt.

But I think, that if you have a good servo (metal gear, enough torque) with a good linkage and an appropriate door-opening-and-closing mechanism (there are various methods) and you keep an eye on the mechanism during the season and do a little maintenance here and there (removing debris, controlling smooth operation), you donít need a back-up-system just for the retract.

Andy
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Old Sep 24, 2009, 07:41 PM
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Killingworth CT
Joined Nov 2008
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my 2 cents

For the few dollars it costs for an extra battery and switch, it seems foolish not to go that route. I would certainly rather be safe than sorry. It only takes 1 time to cost many thousands of dollars.

Change please
lb
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Old Sep 24, 2009, 08:39 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Ok, to add a little more to this, I can give you a specific example of what happened to my 10.3m 1:3 scale Eta. It had the retract door hinging system noted in another recent post in this forum - very friction free hinging.

I had a Hitec HS5945 High Torque digital hooked to a double shocked, well balanced Hock retract. I tuned the system, removed all points of hangup and all friction generators. On my first two outings to fly the Eta I had four battery packs in it but I did NOT have a fifth one specifically for the retract.

My second session of flying nearly ended in catastrophy. During a take-off on grass, the wheel picked up a small twig that got jammed in the retract and stopped it from closing fully. I was unaware of the issue because at that time, I had my retract tied to my tow release and therefore the retract only attempted to close once I was at 1000 ft and I released from the tow.

My ONLY indication that something was wrong was the voltage readouts I was receiving back from the Telario that was onboard. Over a period of about 8 seconds, the voltage readouts from the telario were 6.4V.......6.3V.....6.2V......6.1V.....6V..... Obviously a problem with the power in the system.

I deployed full flaps, full spoilers and came down very fast and bellied onto the grass and cracked one of the gear doors. The Digital servo had been stalled for a number of minutes and was smoking by the time I got it on the ground.

The moral of the story is that even with due diligence in design and maintenance, this ONE mechanism, if jammed, has the power to bring a model to the ground in a way you prefer it not!

As Len added - it's a relatively low cost insurance policy.

Of course, if we were all to take a leaf from the power guys, we'd be using air driven retracts. I can't imagine why we're not - it has its benefits.
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