Servoless electric retract installation

[leccyflyer]

I've got a few sets of the servoless electric retract units for installation in small -medium sized electric models- a set of the expensive Eflite ones and a couple of sets of the budget units.

 

I must say I was very pleased with the speed the retract operates at - no need for a servo-slow there, it's a nice solid, smooth operation, rather than the "wham-bam-thank you maam" of some mechanical retracts.

 

Has anyone used these yet and what provision did you make for battery back-up? I'm loathed to just run them from the receiver battery, just in case anything jams up and kills the battery.

 

How did you go about installing these?.

[NigelH]

The good news is that the E-Flite ones come with srtall protection. Hobby King claim the same about their own/. If something stops a retract from moving, after a second or so, it will stop moving until you move the retracts in the other direction.

 

Watch this video for all the proof you should need -

 

http://www.youtube.com/watch?v=5TmmjCbyPTQ

 

Installation - just screw them into a firm base.

 

[andy watson]

Just tried to embed a video of RC lander ones in my Vulcan thread. Not worked (the embedding, not the retracts) but there is a link there as well.

[Idris Francis]

see http://www.modelflying.co.uk/forums/postings.asp?th=48091&p=2 for all sorts of problems with E flite electric retracts - exceessive current due to lead screw drive, hit and miss operation, mechanisms sticking to to inadequate margin of torque and tolerancing problems

Also Y leads that come apart under their own weight,

Never ever use off Rx battery - asking for trouble

[Bucksboy]

Mine however, are a delight. I've read the link above and some of it makes sense. However, the electric worm driven retracts are the best available at the moment, thats why they are so popular.

i remember all the hours I've spent fiddling with mechanical retracts/ air systems. I was going to use a seperate battery but after taking advice i use the receiver battery. I have got telemetry for the rx pack so i do keep an eye on it though. They will continue to be popular until a better system comes along.

[GrahamC]

I am the very happy user of a couple of pairs of the budget hobbyking ones. I've a set of the 4.7kilo ones in a 62 inch Spitfire with a set of sprung oleos which have proved very reliable indeed despite one them regularly getting a dose of oil from the exhaust! . I also have a set of the 2.5 kilo ones shoehorned into a 46 inch mosquito and retracting to the rear. They too have performed flawlessly even though I have yet to master the art of smooth landings on the mosquito! Both sizes have stall protection, although it seems a little more sensitive on the larger units.

At less than £15 a pair delivered to the UK I'm very happy indeed!

[Idris Francis]

In rely to Bucksboy - I am pleased of course that you have had no problems, but many others clearly have had. Just a few points as no need to repeat previous postings:

The drive mechanism is a leadscrew not a wiorm drive. The first is in effect a nut driven along a thread, the second is a thread revolving against the edge of a toothed worm wheel. Both very inefficient, but the leadscrew is the worst. Unless of course large enough to allow ball or roller bearings to eliminate the basic problem, high frictional losses at the rubbing surfaces,

As others have reported and I found, the sliding fits of the cross-shaff in the machined slots can be too tight in places, due to less than perfect machining. Can be fixed with a file, but it is necessary to disconnect from the drive rod to be able to feel where the tight spots are. Not easy.

On mine the sideways clearance for the blocks to pivot were non-existent, causing more friction.

The result of the very poor efficiency is little pull in reserve to overcome friction, the need to fit stall-protection that would otherwise not be necessary, and all too easy to trip the stall protection and trigger unwanted cycles.

Also, for whatever reason, one a cycles starts - due to a glitch or wyhatever - the design is such that it cannot instantly reverse to correct it, but has to complete the cycle - a second or two.

I experienced many unwanted cycles just on the bench when installing.

In response to Graham, I have no experience of the Hobby King units, but others commenting on these matters elsewhere have reported problems.

I do not need stall protection on my retract servos now bolted direct to each unit, stall current is not that bad.

[Bob Cotsford]

I'm using the 4.7kg HobbyKing units in an AT-6. The retracts are supplied from one socket of a Y lead, with the other socket going to a seperate nimh pack via a switch, the third leg (plug) has the red (+ve) wire removed from the plug and goes to the receiver ie it connects via the -ve and signal wires only.

As they only operate for 10 seconds or so per flight and have their own power supply I have neither measured nor care how much current they use when moving. So far they have been completely reliable when lifting 3 1/2" wheels.

[Idris Francis]

I must have a look at the Hobby King units, see what problems others have found, and see what the mechanism is. If a leadscrew I would not be at all keen, due to inherent inefficiency, and high drain if they do stall.

[Bob Cotsford]

Yes, they are leadscrew. Inefficient maybe, but as historical use shows they do provide an efficient locking mechanism.

[Idris Francis]

Yes, indeed they do. I did not mean to imply that leadscews have no uses, only that (unless using ballraces) the frictional losses make them quite unsuitable for transmitting power when efficiency is important