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Old Mar 13, 2011, 03:41 AM
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mungrelv8ute's Avatar
Belgium, Flemish Region, Sint-Katelijne-Waver
Joined Apr 2003
323 Posts
I recently had a servo on the retract fail in my glider which ultimately pulled the power system down and the model crashed, despite the fact that I was using a "brand" name power board ... :-(

The lesson learned is that where a servo has the possibility to be stalled then you need some sort of overload protection. What the glider guys use is these from Emcotec

http://shop.rc-electronic.com/e-vend...&t=6&c=17&p=17

They plug in-line and once programmed protect the circuit from over current draw. They reset after a few seconds and the servo will operate if it has been free'd.

These might be a solution for the gear doors when using servo's to drive them.

Gregg
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Old Mar 13, 2011, 05:05 AM
DominicM
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Fleet, Hampshire, UK.
Joined May 2003
2,368 Posts
I'm pro electric. Will never use air. Had 100s of flights on electric retracts and only had a problem when I broke a gear on a hard landing. Intending to go RC Lander or eFlite on a large EDF project if the weight comes out as predicted. The only problem at the moment is finding the right struts for each project.
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Old Mar 13, 2011, 05:26 AM
There was a crease in the plan
Steve Haynes's Avatar
Joined Jun 2010
1,332 Posts
Quote:
Originally Posted by ditchit View Post
I'm pro electric. Will never use air. Had 100s of flights on electric retracts and only had a problem when I broke a gear on a hard landing. Intending to go RC Lander or eFlite on a large EDF project if the weight comes out as predicted. The only problem at the moment is finding the right struts for each project.
Strut is my problem too.
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Old Mar 13, 2011, 06:33 AM
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stoneenforcer's Avatar
United States, FL, Mt Dora
Joined Feb 2007
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im using eflite 60-120's with tam struts. very nice!
nice to having overload protection too
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Old Mar 13, 2011, 07:05 AM
DominicM
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Fleet, Hampshire, UK.
Joined May 2003
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Which Tam struts? Can you please give me a link to them on his SHOP because I can't find them. Cheers.
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Old Mar 13, 2011, 02:47 PM
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manchester uk
Joined Oct 2003
34 Posts
enyone seen these UK available electric retracts from www.bobsworkshop.co.uk BB airless retracts for larger models, might be of interest to some for larger models (too big for me at the moment) ...Dave
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Old Mar 13, 2011, 03:07 PM
DominicM
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Fleet, Hampshire, UK.
Joined May 2003
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Not heard of this guy. Thanks. Could be a good option for me. Like how the gear door sequencing is built in.
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Old Mar 14, 2011, 10:30 AM
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USA, CA, Marina del Rey
Joined Jul 2010
553 Posts
if your nose gear is half down and you land on it, chances are you will strip the worm gear, this is probably true for the mains also since its the same principal but i haven't seen it happen.

the only way to combat it would be to get metal gear retracts, however, i'm sure this would just pass the stress somewhere else!!

Kim
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Old Mar 14, 2011, 11:29 AM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
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Quote:
Originally Posted by lightningmcnul View Post
if your nose gear is half down and you land on it, chances are you will strip the worm gear, this is probably true for the mains also since its the same principal but i haven't seen it happen.

the only way to combat it would be to get metal gear retracts, however, i'm sure this would just pass the stress somewhere else!!

Kim
I think this may a potential problem. With mechanical actuated doors there could be an over current draw when the doors are opened at high or even intermediate speed. Then what? Would be highly inconvenient when attempting to land with empty main packs.
To bypass this issue one could use servo actuated retracts and use a servo saver lever. The worm gear design would not be able to handle the stress. I have been thinking to convert my C36-1 (spring-air) to servo instead converting it to worm gear drive for a while. This would be by far cheaper as a conversion kit as well. One would need a roamy fuse tough and one would be in need to integrate the servo to the retract mechanism for minimal issues (short, slop free linkages).

I think the e-retracts would be very nice if there is a weak spot in the drive that doesn't break unless additional spare worm gears would be included with the system. I am not even sure if this is a replacement item like servo gears

If one use mAh telemetry sensors one could monitor the battery pack and prevent a drained pack by alarm settings I always thought more hardware is potential failure but I changed my mind a while ago and now I think I should have more faith in electronics over potential Lipo failure.

just my 2cts
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Old Mar 14, 2011, 11:34 AM
1.21 Gigawatts!
Steph280's Avatar
Irvine, CA, USA
Joined Oct 2000
7,348 Posts
For those looking for struts, this place has a good selection:
http://www.smartmodel.com.hk/product...sub_cat_id=251

IMHO electric retracts are here to stay, and will probably become the dominant system once more options are available. Just like with any new technology, there will be resistance to change for some people. Remember these type of retracts are still in their infant stages, so there may still be improvements to be made. So far I've found E-Flite retracts to be very reliable, even used at their maximum rated weight limit. On the other hand, there are talks about ChangeSun (CS) and HobbyKing cheapies with failing end point switch. So just like air system, you get what you pay for.
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Old Mar 14, 2011, 01:55 PM
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Denmark, Nordjylland, Gistrup
Joined Aug 2005
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Don't forget Lado, there should be some new larger retracts right around the corner http://magnumrc.com/lado-electric-retracts-c-41.html
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Old Mar 14, 2011, 02:30 PM
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Luzern/Switzerland
Joined Aug 2008
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Ron, thank you for bringing this to our attention.

Your current thoughts is what I fight with my friend each and every weekend.

Now all my Jets are Electric Retract Powered, and those are all 90mm Jet's.

He is using 2Way Valve Air Retracts and also 1 RC Lander New Alu Retract System for the Mig from flyfly hobby.

Now the RC Lander Nose Wheel retract stopped working after the 4th Time, extending and retracting back in....and that happened during flight.

Now the nose wheel comes up with a stutter effect and goes down with a stutter effect.

He hates the electric retracts but had a fight this weekend with his 2way retract system...he is pumping and pumping and pumping and air leaks somewhere...anywhere..lol.

He got mad and it took him 1 Day to find the failure, which were 2 leaks on 2 different locations with the most expensive air cable's.

I use Freewing Retracts right now on my F-18,F-4 and never had any trouble.

If something brakes, I buy a single thing and replace it. Saves time and a lot of nerves!

However now for my Spark...I have the choice between air retracts from Tam or Electric Retracts from Tam which are a 100grams heavier then the air ones, due to the eflite retract system.

I got told to hold the weight of the Spark between 4-4.5kg..so each gram counts..

I will however may do the choice for the electric version...less pumping and pumping.

Regards

NS.
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Old Mar 14, 2011, 07:50 PM
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United States, TX, Fort Worth
Joined Jan 2011
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I too have the freewing electric retracts and have never had an issue. I am waiting on my set of RC Lander above 90mm electric retracts, these are going in my HET fiberglass F-18B. Can't wait until they arrive.
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Old Mar 15, 2011, 01:54 PM
You are a "go" for reentry
Maxthrottle's Avatar
High Orbit.....
Joined Jun 2009
6,247 Posts
Some of the guys request someone start a Comprehensive Etract List over in the warbird section.

The Etract concept has many advantages and is being improved on.

The concerns over striping the worm gear is unlikely because of the mechanics of the trunnions movement. To, worm gear have far greater actuation force as the load is fully spread across the mechanics of the components used and not on the motor.

If you ever wondered how those big dishes that used to be in everyones neighbourhood moved around... it was a worm gear. Even in very bad weather it could hold the dish.

These all vary in there grades and do encounter some complications but are usually of the same nature found with air. Getting the sequence of doors to work with the sequence of the gear.
The best way I've found is a good sequencer like an RCBEE also used for air; or a gear slower match box etc.

If you can jam an etract just by using it, it is more likely the one used may have been out of its weight class which does have to be followed. Otherwise the overload cutout stops the sequence and you gear back down. Like any component in your RC setup, etracts can be powered independently or from a main pack with a BEC or matchbox.

One advantage though is they are far more affordable. Even if you trash one, they are generally only under $20 each.

I've generally used them at 6V and haven't encountered issue having used 7 different sets. Freewing, PZs which are the ones you see RCLander carry, Hobby Kings, Hobby Partz etc in a PZ15090 which is a 3mm strut or the PZ15091 which is the 5mm strut. Also Change Suns very nice low profile with its trunnion and block made of metal; so very hard to strip. The smaller CS and 15090 will handle 2.5kg etracts and the 15091s 3.5kg. But if you push them harder than this, which I have, they will ware down quicker.

I've also looked over the Eflite versions which are similar in construction. The All metal RCL and Eflites and Lados are even that much better.

There over all weakness is QC. Some have complained of getting bad boards even for Eflite (though there quality check and service makes up for rear failures). This is more so because we are seeing the first versions of the concept. But at $7-14 for the PZ15091s you can get another set while you fight with the vendor to replace the other.

These are all taking the hobby in the right direction since the are simpler, weigh less and are less prone to failure as they have less points of failure. They are still in their infancy but even the ones that are out do fairly well. As we see further renditions of them it'll only get better.
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Old Mar 16, 2011, 02:05 AM
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USA, CA, Marina del Rey
Joined Jul 2010
553 Posts
Just to clarify, stripping the worm gear is not just a concern, i have seen it happen on more than one occasion both times with eflight retracts, and we know that air does not have this problem.

I'm in no way against etracts and will actually be buying some in the next couple of days for an edf I'm finishing but i do know there are problems.

I don't think its a fundamental design issue i just believe that they need to use better materials in their construction,

on both occasions eflight replaced the nose gear for free, which is fantastic but does not repair the damage to the plane!!

To summarize i will use etracts for certain applications but not for others and they must be high quality!!!
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