E-flite electric retract discussion

[Fred Keegan]

Have just fitted some 120 size E-flite electric retracts to a 72 inch span B17, much easer than the air ones I removed

[Craig Carr]

Looks excellent Fred,

 

I think these sort of units are going to become more and more popular

 

Have you got build thread on the go for the B17, looking very good so far Which plan you working from?

 

Edited By Craig Carr on 04/02/2011 19:00:25

[andy watson]

Hi Fred.

 

I have been thinking about those for my new Vulcan, but was (slightly) put off by the comments in the mag about the wire legs. I am thinking about the RC Lander equivalents instead, as they have matched oleos as an option.

 

Can I ask the weight of the B17, and can you let me know how they get on?

[Fred Keegan]

There is a build thread on this site, you w.ill have to look it up, as I said befor I had to put it on hold due to ill health

[Tim Reeves]

Hello Fred

I have also just purchased a set of these retracts. Would you still need or best to have a seperate battery to operate them?

[Tim Hooper]

Tim,

 

I have a smaller set in my electric-powered Courier, and power them (and the flight servos) via a Ubec.

 

I was a bit hesitant about linking them in the same circuitry as the servos, but as they can't be stalled mid-cycle I went for broke. No probs so far!

 

tim

[David Ashby - Moderator]

Tim R - think of them as two powerful servos and then judge from there depending on the model and set-up. In most cases a UBEC or, better still, a separate Rx batt would be required.

 

 

 

 

 

[Tim Reeves]

Thanks for the replys.

I have fitted the retracts into a PC9 1.6m (powered by a four stroke engine) and have played safe and fitted a sperate Rx battery. More for peace of mind.

Thank you Tim

[chris henton]

Hello Fred,

 

Is your B-17 the Tony Nijhuis kit?

 

I have just ordered a set of Ripmax SkyRC retracts for mine.

 

Was it this set that you removed?

 

Tony recomended the Ripmax items but i would be interested as to why you moved to electric retracts and what problems the air retracts were casuing for you?

 

Regards

 

Chris

[winchweight]

Are they 120 sized as in they will cope with models running a 120 sized engine?

 

I ask as I have the BH Trojan 120 and I am looking o replace the rubbish air retracts they come with. The electric retracts I have seen elsewhere are £300 for a trike set!

[Chris Bott - Moderator]

Posted by David Ashby - RCME Administrator on 29/03/2011 09:57:54:

Tim R - think of them as two powerful servos and then judge from there depending on the model and set-up. In most cases a UBEC or, better still, a separate Rx batt would be required.

 

 

 

 

 

I'm not sure it's that straightforward a decision. They are designed to detect being stalled and to stop drawing current. So the usual worry of say a leg getting bent on takeoff meaning the retracts catch on the way in, stalling the servo and flattening the battery sounds like it's been designed out. I think!

[David Ashby - Moderator]

Posted by Shaun Chant on 06/05/2011 21:00:35:

Are they 120 sized as in they will cope with models running a 120 sized engine?

 

I ask as I have the BH Trojan 120 and I am looking o replace the rubbish air retracts they come with. The electric retracts I have seen elsewhere are £300 for a trike set!

Hi Shaun

 

My feeling is that it depends on the weight of the model. Say up to 12lbs then yes but not really when you're at 15-16lbs where I feel oleos would be better.....although if you can fit these to the leccy retract unit then all well and good.

 

Chris - yes, spot on, I was was really adding personal pref here. I use separate rx batts in larger electric models.

 

 

 

 

[andy watson]

You can certainly fit oleos to the RC lander ones- they simply have a metal rod sticking out that the oleo slips over.

 

The RC lander ones look identical to the e flite ones above, and are also described as 1.20 size.

[winchweight]

Ok, thanks. I have gone back and looked at the Lado ones and they are soooo expensive, although I am sure they are good quality.

[Jim Mann]

Must admit i purchased the eflite 120's and added the oloes i had in the kit for my blackhorse fw190. only need to open the aluminium collet to take a 5mm hardened shaft ( borrowed from a motor) couple of flats added and works an absolute treat. Only issue i have had is one of the worm gears has backed out the cam...not big issue and should be easy sorted.

[Myron Beaumont]

I've two sets of the HK retracts .Why do you all fork out a fortune for the eflite ones ?

[Frank Skilbeck]

Posted by Myron Beaumont on 13/03/2012 21:50:37:

I've two sets of the HK retracts .Why do you all fork out a fortune for the eflite ones ?

Mmm I have a set of HK ones that came in a Mig15, the nose leg broke pretty quick and had to be replaced and after 10 months or so one in the main wing has started cycling up and down of it's own accord. Fellow flier has a set of e flite retracts in his Habu (same weight but a bit faster) and they've been faultless, as have the ones I had in my Parkzone P-47.

[Myron Beaumont]

Frank

Maybe they're not the same ones I bought not in an ARTF but as seperate items .Don't have any experience of nose wheels so can't comment

[Frank Skilbeck]

Posted by Myron Beaumont on 13/03/2012 22:35:55:

Frank

Maybe they're not the same ones I bought not in an ARTF but as seperate items .Don't have any experience of nose wheels so can't comment

I've looked at the ones from HK, but there are so many it's difficult to sort out the good from the bad, at least with E Flite you know what you are getting and have UK based support. The larger E Flite ones are of metal construction and are very nice.

[Jim Mann]

Posted by Myron Beaumont on 13/03/2012 21:50:37:

I've two sets of the HK retracts .Why do you all fork out a fortune for the eflite ones ?

I actually bought 4 off the HK... http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14838 but they are rated at 4.7kg.

The blackhorse Fw190 is 4.8kg...so err on safe side i went with the eflite and i have to say they are well made .. solid but there are a couple of niggle for elfite to address

motor wires are easy to break off and are not protected..they are coated in silicon so a bit difficult to solder.

if you tighten up all the screws, at least on mine, the overload protection kicks in and does not move the gear..kepp it "nipped" and its fine

so the cheap ones from Hk wil do as a back up when i am flying. best of both worlds

[Idris Francis]

It is more than 40 years since I used to fly a 14 lb 64" Sterling Spitfire with an unsilenced Miles 10cc racing engine, using mechanical retracts with barely noticeable slop, both operated by one of my own Flight Link retract servos, that would not drain the batteries significantly even when stalled - and all runnng of a 500mA Nicead pack! We seem to be going backwards......

I have just binned an inexcusably expensive pair of Robart servo-operated retracts fitted in a 63" TopFlite Thunderbolt because of excessive and uneccaptable slop when up or down, a tendency to stick and for even a 17kgcm retract servo to fail to pull the wheels up more often than not. I re-worked the badly dimensioned parts to be marginally acceptable, but as operation was marginal I had no choice but to bin them..

I replaced them with a pair of E Flite 60/120 electric retracts thinking that these would solve my problems - but they are unusable and will end up either in the bin or sent back as not fit for purpose.

First some simple design errors and/or /quality control failures:

The locking screws that hold the legs to the alloy trunnions should be as deep as the hole to minimise the risk of stripping threads - they are only 2/3 of the depth.

Rule No One when trying to lock a shaft into a hole (as I found out when manufacturing 1m plus joystick controls for industry etc) is to make the shaft as good a fit as possible to minimise slop that can lead to movement that can lead to chafing and loosening. The fit of the leg in the trunnion is not as good as it should be, the fit of the axle on the leg is even worse - the old expression "it fits where it touches" applies. Ditto the wheel collets.

Rule No Two, for locking screws, is never put two in line, as they in effect provide a bearing on which the shaft can rock. One is better than two in line, better still is two at 90 degrees, better again is two at 120 degrees. It costs a penny more but does the job properly.

Not that these points matter much to me - I solder everything to make sure.

The axle shaft is strangely small in diameter, needing sleeving even for new wheels.

Now for the critical design error - the lead screw.

Simple energy calculations show that with 100% efficiency the power needed to lift a 4.4 ounce leg and wheel 6" in 2 seconds corresponds to 20 mA at 4.8 volts (less if a compensating spring were fitted with optimum geometry.). So close to 98% of the 1 Amp needed to lift each Thunderbott legs - and then only just - is lost. Even if we assume motor efficiency as low as 30%, that means that the lead screw is working at something like 6% efficiency.

Is this surprising? Not in the least - leadscrews are notoriously and inherently inefficent because so much energy is lost rubbing the threads together as they turn. Leverage of 6" to 1/2" means that at worst geometry the 4.4 ounce wheel puts an end load of 3 lbs on those threads, and the necessarily fine pitch means lots of turns.

If I had been designing such a retract this basic arithmeticI would have ruled out a leadscrew on its own. However even one stage of gearing (say 3 or 4 to 1) in conjunction with a coarser pitch thread would improve efficiency - either as more power in reserve or lower drain meaning smaller batteries by similar ratios.

It is the fundamenta,l error of using such an ineffiicent mechanism that leads to the need for obverload trips, which as I find and others report on this web site, can lead to unwanted cycling of the controls. None of this would be necessary with a better mechanical design.

Mty own bench tests this morning, using only a 1,200mAh NiMH battery, receiver and 2 retracts, with Tx two feet away, established that the retracts do work but - crucially - not every time, Holding one leg gently as it tries to extend I sense at least two sticking points, as if a thread problem, For this reason they can and do stick part way - and in my view the threaded rods and followers are unikely to survive a touch-down in that position.

Worse, even in these optimal bench test conditions, as at least one other comment on this web site has noted, the units often cycle, either way, and often for no apparent reason. Something appears to be triggering the overload trip - even though there is no apparent cause such as jamming ot sticking. Sometimes however something as simple as touching a screwdriver on a mounting screw of one unit can trigger that unit or the other one to cycle - and not just once!

For all these reasons I would not dare use them in an aeroplane. Whether I can adapt the drive mechanism to take advantage of the slop-free locking, either by fitting one gear stage or a push pull link from a servo, I do not yet know but my next step is a bench test of the 40 year old units with the powerful retract servo.

Hope this helps others. see short 2nd part next

[Idris Francis]

Part 2

I forgot to mentjon the daft cable lengths. What is needed , obviously I would have thought, on each unit is a lead long enough to reach the centre of the wing, and then a short Y lead to join them.

Instead we are given a lead that needs to be plugged into the Y lead well inside the wing, which is of course impossible. That is to say, it can be done by dragging the Y lead through the wing to the retract position and connecting it there - but then the other end of the Y lead is too short to do the same on the other side. So I ended up having to cut, extend and join the leads.

 

As not infrequently happens, I seem to find problems when others find none! Another example was 15 years ago when I found that the HAL autpilots use a 12 mhz microprocessor signal that inflicts serious interference on 35mhz Rxs, reducing the range by at least 25% and often much more (down to 5 yards with one dual conversion Rx!) I managed to filter out all the noise to reduce loss of range to trivial proportions.

 

Edited By Biggles' Elder Brother - Moderator on 28/06/2012 19:34:47

[Idris Francis]

I also forgot to mention the battery voltage tests I did this morning - albeit 1,200 mAh NiMH is too small a capacity for these retracts: No other servos, bench testing, readings at Rx terminals.

Idling 5.4 volts

Operatoing 4.8 volts

One stalled (for no apparent reason) 4.2 volts.

I would never fly without a throttle fail safe that also detects low battery voltage. Under the above conditions a leg that jams trips rthe throttle fail-safe giving low throttle. Last thing I need!

For these reasons I would never use these units - regardless of the other problems - except with a separate battery. And then much bigger than 1,200 mAh

[Tim Mackey]

I have threee sets of these E Flite units, of different sizes and all have performed faultlessly over around 50 /60 flights.

Short and sweet, with no links to self publicity of websites

[Former Member]

[This posting has been removed]