chuckk2

The other day, I bought a Hanger 9 P51 (40), HAN4440. The same plane is also offered in a "trainer" version with engine, etc.
At the same time, I also bought an E-flite 60-120 85 deg. electric retract set, and some other goodies from my local hobby store.

I believe in testing all the electric parts prior to install, just to save problems. Retracts are one of those things that require some level of modification when installing, so
the electric retracts made the top of the test list.

Test methodology
Servo tester and digital pulse width readout,
4.8 VDC 2000mah NMIH battery at just over a 5.2V charge level 4A max rated current draw. I later also added charge to bring the NMIH pack to 5.6v or so (no change in test results)
4 cell conventional AA PB cells in a battery holder (Higher voltage no load, sags a bit under heavy load(but not too much), cells not brand new, works fine for testing servos) ~1.4 v per cell.
(I also tried using 4 brand new AA Pb cells with little difference in results.)
Used rubber footed clamps to secure the two retract units by mounting flange (so they don't flop around on the bench, etc.)
The retracts are shipped in gear up position.
Three pulse widths are of interest.
1500 (1.5ms) (Default power up for many receivers before any presets are in effect)
~1331 Gear down (1.33ms)
~1690 Gear up
Expected operation starting from the gear up position.
As the pulse width passes 1331, going towards 1000 the gear should extend.
As the pulse width goes from below 1331 to more than 1690 the gear should retract.
The servo tester has a variable pulse with knob, and the readout shows the approximate pulse width between 1000 and 2000

Observed Behavior using the Pb cells
Very erratic, gear would usually not extend, and a short motor run when the pulse width was about the gear up spec.
Occasionally one or the other gear would extend. At one point, they were totally out of sync, with one going up, and the other down.
Usually both would not extend, or perhaps one would extend.

Once extended, both gear would retract. Once retracted, additional erratic operation occurs as above.

On to the NMIH battery
Behavior more or less as normally expected, with very occasional no gear extend, or one gear extend. Seems to be somewhat dependent on the rate of pulse width change.
It may require more that one pulse width cycle to get the gear to initially sync and work properly.

Conclusion.
The gear favors the up position, just the opposite of what is expected and usually required in full size A/C. (The gear would never begin to pass general FAA guidelines.)
A separate power source from that used for the receiver, servos, etc. is really a good idea!

In the last few months, I've observed a couple of scale warbirds using these or similar electric retracts go through one gear or no gear down sequences, with an eventual belly landing.

28 June - - further testing - -

One main gear works a little bit better than the other, in terms of operating reliability at higher voltage.
It turns out that the gear mostly works properly at about 5 to 5.6 V, and really acts up above 6-6.5v or so.
The gear is spec'd to work properly between 4.8 and 7.4 vdc, and it just doesn't do it!
Initially, I assumed, incorrectly, as it turned out, that a Pb four cell pack, with each cell putting out ~1.4 vdc, was a good choice for testing, since the cells were
older, and likely not as current capable as they were new.
It turned out that the other power source, a four cell Tx pack, using 2000mah NiMh cells was more current capable (4A rated) at it's level of charge, was at about 5.5vdc.
(And it worked much better, but complete reliability was still lacking.)

???????


Conclusions
1. Obviously, out of the box, Does not meet operating voltage specifications of 4.8-7.4 vdc
2. Favors gear up, rather than gear down during incorrect operation. It's even possible to get the gear totally out of sync and have it go to gear up, then fail to respond.
3. This is far from required/desired operation, to say the least.

Hopefully, my local hobby shop will receive a new shipment tomorrow, and we will see if a new production set behaves as it should.
For giggles, I even tried adding a servo to the mix, much as if it was used to control such things as gear doors and a sliding canopy. Naturally,
it worked properly under all the test conditions.

6/29 Further testing results
AH HA!
Stopped by the local hobby shop with all the testing bits and pieces. A new gear set straight from the box showed similar undesired operation.
Using a JR Matchmaker, things improved. Scratched head, as this was not what I had expected to happen.
While I was at the hobby shop, I used the opportunity to buy a servo/receiver voltage/current meter.

To shorten a long story, after supper, at my bench, the servo current meter showed that the retracts were binding, and activating the built in over current protection.
This was occurring at about 1 1/2 A current. One gear was more prone to this than the other, and the binding/over current usually occurred just as the gear started to extend from the up position stop.

I loosened the 3 side plate screws, and things improved. Watching gear movement, I noticed that the brass "T" on the highest current gear had an odd movement about the time that the gear bound, and went into over current shutdown. I rotated the brass T 1/2 turn to switch ends, and tried again. That helped reduce the over current and binding. The gear circuit board has miniature limit switches that contact the brass "T" when the gear is at the full up or down position.

Eventually, with a bit of fussing, a few drops of instrument grade oil, etc. I was able to reduce the current draw for both gear operating together to about 300-400 ma, and get both to move at the same speed.

The interaction of binding, over current shutdown, battery voltage, and battery voltage sag under 1-1/2 A load caused confusing results at various times. I also tried a "yellow box" servo tester and an AR600 receiver with various batteries.
The Servo tester, AR600 receiver, and the JR Matchmaker each behaved slightly differently, with the AR600 LED going out during high current draw. This is not good, since it showed that the gear binding can cause a loss of A/C control. We used three different types of batteries PB(AA cells), two NMIH 4 cell 2000Ma packs, and an LiFe two cell pack at various times during the testing.

I might be able to reduce the current draw further by polishing the sliding surfaces on the side brackets and the gear forks, but have not, since that is time quite consuming.

At this point, I'm more worried about the behavior than anything else. If this is typical, then I'll return and use an alternative. If not, then warranty replacement is available.

Any experience, comments, suggestions, etc.?

Idris

Pleased to read this, confirms my very recent experiences with the first - and almost certainly the last - of these units I will buy.

Rather than repeat material I have just posted elsewhere today, please refer to http://www.modelflying.co.uk/forums/...91&p=2#1218304

There are several design defects, especially the use of the 6% efficient leadscrew - simply not sensible and many problems related to current draw relate to this. Incliding the motor the overll efficiency is of the order of 2% in terms of energy used and energy put into raising the legs

chuckk2

I'd have to say that I agree in part, and differ in places.
The Lead Screw thread is too fine for longevity. A geared motor might allow a larger diameter Lead Screw with a more coarse pitch. I don't like the number and type of bearing-less sliding surfaces.
Design "defects" are not really defects when compromise is necessary to meet price. There are always better ways to do something when price is not the major factor.
I could easily design and with difficulty, build a retract gear assembly that works well, is complex and expensive, and never get back my investment due to low volume sales. It's hard to justify a gear set that costs more than the basic plane it goes in.

vasek

My Feedback: (4)

Thanks for sharing! what digital pulse width readout are you using?

V.

Idris

I would be interested to know which points you disagree on. None of the testing I have done seems to me to have shown up any errors in my assessment, and indeed (just like being in the EU) the more I know the worse it gets!

When I have completed tests on both refurbished 30 year old all-metal retracts (one is working perfectly, the other has a little slop to sort out) I will post here results for the E Flite and the old ones

Idris

I am using a Hitec Eclipse on PPM, so pulse nominal width of the control pulse is 1msec to 2msec with neutral at 1.5msec, plus the programmable variations.

I also have a Hitec Aurora 2.4gHz, not yet flown or used to check the E Flite retracts

chuckk2

That is more or less standard these days.

Idris

The following is my summing up, just posted in response to a chap on http://www.rcuniverse.com/forum/m_10...m.htm#11151185
who found when he dismantled his units that much of the problem arises from inadequate clearances on the moving parts, causing them to stick and jam.

"for information.

Thanks for your most helpful post, confirming as it does - and more - my findings. What follows is intended to be my final assessment of these units:

As before, the fundamental design error is the use of a lead-screw, notoriously inefficient at transmitting power because of high frictional losses inherent in rubbing the two threaded surfaces one on the other. Unless of course a ball-bearing lead screw were used, though unlikely to be available in this size or suitable for the forces involved if it were. Nor does the small size of the motor help efficiency.

Having now removed the drive motor and electronics (using a cutting disc as I cannot find a Hex key to remove the screws) I can confirm that what appears to be just a motor driving the in-line lead screw does in fact have a tiny 3 stage gearbox built in to the end. I suspect that in those small sizes with a small number of teeth efficiency is not too good, It is at least arguable that were the overall gear ratio and the thread pitch both twice as great the inefficiency would be significantly less and available pull significantly greater. In my view the speed could be halved to improve force, and still be fast enough (though as doubling the ratio would also double the force, speed would not fall by that same factor of 2)

This might go some way to reducing the several problems which arise from such low efficiency:

1/ The system struggles to overcome friction in the lead screw and (as you mention) in the locking pin etc. My own test on a complete unit, done by holding a finger lightly against the wheel when it is being raised, shows that available pull before stalling fluctuates a great deal - a graph would be a saw-tooth. This is because of the less than perfect fits and surface finishes moving one on another. In my case the margin for error - the difference between worst running current and electronic trip - was so small as to be unusable, the slightest touch would stop the wheel moving.

2/ 5 cells instead of 4 made marginal improvements but nothing like enough to make it reliable.

3/ One time in 6 or so, one leg or the other would refuse to unlock and extend.

4/ Unwanted cycling of the controls, presumably because of the electronic trip being activated, occurred quite frequently. At times merely the metal to metal contact of a screw touched against the mounting frame would cause one or other unit to cycle.

5/ On 4 cells the maximum current when the legs continued to move, for 2 units, was close to 1 Amp. When stalled 2 Amps with a buzzing sound until the trip activated after 2 seconds or so. On 5 cells it was 2.7 Amps.

6/ Because such currents would cause terminal voltage of normal Rx batteries to drop to dangerous levels - loss of decoding, delayed recovery, and slow throttle fail safe activating - I would not dream of operating them from the Rx battery even if I could make them work reliably - unless perhaps in the smallest size - and in my view and those of others I have read, using the Rx battery is just asking for trouble.



Having removed the motor and cut off its lead screw I could operate the unit by hand. It immediately became obvious that the transverse locking pin was marginally tight in it slot, on one side. This caused it to tilt, making things worse.

It was then also clear that the sharp corners in the frames between the locking slots and the transition slots were too tight. There is no need for the corner to be sharp, so careful work with a needle file freed the whole thing up. Before doing so, even without the undercart leg fitted, pulling the linkage free from the locks took significant force, afterwards no force to speak of.
On the second unit I found another problem - movement was stiff even without the u/c leg fitted. Slackening even very slightly the screws that hold the frames together eliminated the problem. This turned out to be because the two plain brass bearings set into the side plates were not quite flush, reducing the effective spacing by about 0.008" which was just enough to squeeze the pivoting trunnion. I linished them flush and solved the problem.
That the fit of these parts is so critical helps explain why some have problems and some do not - all depending on the clearances (which of course have to be minimal because of the 30 to 1 magnification seen at the wheel)

Having removed the drive system and freed up the mechanism I decided that marginal operation and unwanted cycling were simply not acceptable, and the obvious solution would be a more efficient motor with conventional gears. Fortunately I had precisely such a mechanism immediately to hand - a servo!

Initial tests showed that even with a 7" leg and 4 ounce wheel, a bog standard 60 degree Futaba ball race servo would handle the forces involved in one unit. A 17 kg cm 160 degree retract servo would of course do so with torque to spare. Because the aircraft in question is a TopFlite Thunderbolt 64" one, already built, it would have been very difficult to retro-fit the long linkages that would have to pass between the wheel wells and the upper skin to reach the centre servo bay, and bench tests showed that such long linkages need to be very stiff to prevent bowing that would prejudice secure locking at one end. And of course tricky to set up because the locking pins are not visible when installed in the wing.

Plan B was therefore to cut off one of the unwanted end of one of the frames and bolt directly to it one of the two retract servos I had to hand, so that the output arm of the servo was on the centre line of the retract unit. (A single nut and bolt will suffice as long as the far end of the servo is then supported in the wing.) By a stroke of luck I had a steel rod with a threaded end that matches the transverse pin and installed it as a push rod about 2" in length between the locking pin and the servo arm. These being proportional servos it was easy to match the travel to that of the locking positions before installing in the wing.

I had to cut away enough wing skin to allow the servo to fit, but not that much and not difficult to rework. I could have used the frame and servo to reinforce the strucure but on this wing it does not seem to be necessary.

I now have - at considerable overall expense in parts, time and frustration - undercarts which work every time, do not jam up, which lock precisely in place at either end and which have considerably more servo power available than they need - so much so that the servo does not noticeably slow down when lifting the leg. This incidentally confirms a point I made earlier, that the efficiency of the standard unit is of the order of single figure percentage points - because the servo arrangement is so much more efficient it wll not result in excessive drain from the Rx battery.

As for future retract models - at least one of the small cheap units, working on much the same principle as the mechanics of the E Flites, are entirely satisfactory in models up to say 56" span. At least that same unit can have grub screws fitted to adjust minutely the play at each end.

I cannot envisage paying E Flite prices for units that I then have to convert to servo operation after fine-tuning the fit of the parts - I did so on this one occasion because it was the easiest way out of where I had found myself.

I have taken a few photographs that I could put on my web site if anyone wishes.

If on the other hand E Flite decide to offer just the mechanisms without the drive system - as Robart do as an alternative to their pneumatic retracts - and at a significantly lower price, then they would be an attractive option. Especially if the frames were arranged to accept servos bolted on.

All of this and previous postings are of course only my opinion, others are free to disagree, and I have no commercial reasons whateever for making these observations.

Sorry if anyone thinks this long-winded, but I tried to make it complete in itself and as helpful as possible. I will put the same on the few other web sites where I have seen this subject raised.


Idris

chuckk2

Prompted by the receipt of the correct diameter main gear wheels for the Hanger 9 40 P51, along with some 6A BECs, I decided to play around a bit with the 60-120 retracts under load.
Initial results using normal 4 cell receiver batteries showed that there was a momentary high current draw, even when the gear operated properly. I had previously suspected this, even though
the servo/receiver voltage/current tester did not fully show the high current, due to it's short duration. The only reliable indication of the high current was that the receivers I use have a red LED that is lit during proper operation, and it blinked when the gear was just starting to operate. The batteries do not supply enough peak current, without dropping to a marginal voltage level, something less than 4.8v.

Out comes the 6A BEC and a three cell 3200maH LiPo! The BEC is jumper programmable to 5.0,5.5, or 6.0V. I tested gear operation at all the voltages, and, as expected 6.0 V is better.
Under load, with "normal" operation of both main gear together, the initial current is in excess of 1Amp, and drops rapidly thereafter. Due to slow response of the tester's readout, I cannot tell the exact current.
More important, the receiver LED stayed on, and did not blink during gear operation.

Conclusions
Don't power the gear with four cell receiver batteries, even NMIH ones.
It's preferable to use a separate BEC, particularly if you use speed controls that have a built in BEC powering the receiver.

I'll most likely use the speed controls 5A continuous SBEC to power the receiver and servos, and an external BEC to power the gear.
Or, if time permits, I may split the servos, so that the receiver and critical controls are on one BEC and the gear and perhaps flaps and maybe rudder on the other.

Idris

I agree with much of the post about current drain - the only sure way to tell what current is being drawn is to insert a low value resistor - say 0.1 ohm or less - on the power lead and put an osilloscope, preferably a storage oscilloscope - across it. I am no longer able to do this because I have removed the drive systems. However my findings of tight spots of several kinds would certainly cause both the occasional failure to operate and excessive current triggering the current trip.

As these tight spots are caused my minute flaws in the various surfaces they are likely to vary from one unit to another, as in my two, and so some may work OK and others not. As before I decided that the design error, high currents, tendency to stick and/or trip the current limiter and unwanted u/c cycling was simoly not acceptable even with a separate battery, and converted mine to servo operation with 1 servo bolter directly to each mechanism and connected with short linkages. That is now installed and working reliably, with no need for a separate battery.

In doing the retract installation I found a SERIOUS PROBLEM that I have never come across before with new connectors, and only very occasionally with old, tired connectors - and I strongly suggest that everyone checks every connector of this basic type, REGARDLESS OF MANUFACTURER, BEFORE FLYING AGAIN.

I was puzzled when working on my wing to find that the Spektrum retract servo leads separated several times from the temporary Futaba Rx extension leads I was using, despite no force being used. On closer checking by pushing them together and pulling them apart I found that almost no force was needed - in some cases the weight of the cable was itself enough to separate them.

On closer inspection using a single pin from the larger female moulding, test fitted into individual sockets in the male moulding, I found LITTLE OR NO GRIP, and in one or two cases noticeable grip only in the LAST 1MM or so of insertion. As it is the grip of the 3 sockets on the 3 pins that alone holds the cables together this is potentially catastrophic, even if all 3 pins do actuially make some sort of contact - which is less than assured.

This problem applied both to the JR type plugs fitted to the 2 Spektrum retract servos and to the JR type plug of the E Flite Y lead - which was a loose fit even in the sockets at the other end of the lead. In all cases the lead colours were brown, orange and red flex.

I cross-checked grip with Futaba connectors including extension leads and Y leads perhaps a year old - the newest I have - and found that the faults lie only in the NEW SOCKETS in the JR type plugs. I also checked 2 quite old JR connectors on a JR and a McGregor servo and found them to be OK.

I have been assured by my dealer that connectors fitted to different makes of servos etc should be fully compatible (if they fit togethet of course) and there is no difference in specification that leads to this sort of problem.

Accordingly it seems to me that this is a MANUFACTURING DEFECT accompanied by A QUALITY CONTROL FAILURE - with who knows what serious consequences.

It is entirely possible that other manufacturers buy their pins and sockets from the same source, so the fact that I have seen the problem only on on JR plugs might be because they are the only new or newish ones I have - so in my view thorough checks of ALL makes of connectors are ESSENTIAL.

Given the potentially serious consequnces of cables coming apart in service, or loss of even one connection, it seems to me that there is a strong case here for urgent further tests, maximum publicity and quite possibly product recalls.

It is of course theoretically possible that I have just been unlucky - I often think that if there is a defective item on a shelf in a warhouse anywhere in the country it already has my name on it - but the consistent pattern of no grip in every socket on 3 plugs from 2 different manufacturers implies otherwise.

As always, I emphasise that I have no commercial interests whatever these days and that I report only what I find, in the interest of safety.


Sincerely

Idris Francis

Idris

I have found yet more lproblems, but the summary is too long to file here so I have made it available at http://www.fightbackwithfacts.com/re...ctor-problems/.

The same subjects have been discussed at

http://www.rcuniverse.com/forum/fb.asp?m=11184956

http://www.rcuniverse.com/forum/m_11...m.htm#11134586

http://www.rcuniverse.com/forum/m_10...m.htm#10583216

http://www.rcuniverse.com/forum/m_10...m.htm#10549512

http://www.modelflying.co.uk/forums/...91&p=2#1218194

chuckk2

A four digit one that is in a small yellow plastic box. The vendor usually comes to the southeast model show in Perry GA.
(The mfr's label fell off some time ago). The same source sells a servo simulator in the same size plastic box.

David R

I have just bought a set ot eflite 60 -120 retracts and I see characteristics of all the comments on this thrteadin their behaviour.

WhenI installed themI rigorously tested each leg tp ensure that they worked perfectly using a NiMH 4 cell flight battery. A soon as I put both legs in circuit they began to routinely cycle uncontrollably but eventually lock, I was using a Hitec Aurora 9 with optima 7 receiver, the telimetry showed thereceiver battery was 4.8volts. I separated them again and guess what, individually they (appear) to work properly soI just assumed it was something in the Hitec parameters (travel limits or speeds etc). I switched to a JR DSX7 and the problem did not occur using the same flight battery.

After fully recharging the cells the two legs workperfectly with the Hitecbut as soon as the battery starts to loose power they cycle.When in motion the two are not perfectly in syncand it seems that when coupled and one reaches end of travel, the voltage fluctations from the other cause the system to trigger motion again.

so farI have not been able to duplicate the problem with the JR but I have not tested with continued battery discharge to see if it simply has a lower threshold so maybe the JR has a better power output characteristic under load than the Hitec or perhaps pure coincidence.

I dont think that a bigger battery for the flight pack is a solution if the problem is the output from the receiver, it just delays the enevitable.
I considered putting an opto coupler on the circuit so if they started to cycle I couldstop the power drain but landing with mid travel u/C is probably just as damaging so unless I find a reasonto give me confidence I am going to put the legs on a separate battery which adds to the weight but lowers the stress asI dont yet trust the JR will not have the same problem.
Considering the weight of the plane and the need for balance material the penalty of an extra battery is small.

David R

Idris

Thanks, further confirmation of gremlins.

I cannot now remember for sure but I think I tested mine with my Hitec Eclipse 35hmz Tx and any one of several old Rxs I keep only for bench testing. And also with the Hitec Aurora 2.4ghz Rx in the aircraft.

However I saw unwanted cycling even with just one U/C connected, and in any case gave up on them when I realised how little power was in reserve, even at high current drain, at the positions where the inconsisent mechanical fits led to tight spots. I checked this by holding one finger agains a moving U/C leg to establish what force would stop it - hardly any.

chuckk2

Within the last few weeks, I had occasion to buy another EFLG 410 retract set. Given the previous problems in this thread (mine and others), I tested the set
"before the sun went down". The new set draws less current, and is slightly slower that the original sets we tested. It seems to actually meet the current spec's!
I suspect that the motor innards are different, as everything else seems to be the same. (by eyeball)

topspin

Thanks Idris. I have found that JR, Spektrum, and other non Futaba connectors will fall right out of a Futaba servo extension with little or no force applied. One trick I learned is to use a tiny drop of foam safe CA on the top edge where the connectors mate. It is very strong but can be broken and cleaned off easily without damaging the connectors if removal is necessary. Your post kind of sounded like Spektrum bashing to me but I could be wrong.

I understand that you have no commercial interest but I don't see how retracts are a huge safety issue other than impacting the saftey of your airplane to stay in one pice on landing. Bottom line is that electric retracts stink. There is almost always something wrong with them, they break if you don't grease the landing, and except on a cheap foamy I would never use them in anything. For 60 to 120 size I would use Robarts or some other air powered retract system of proven reliability.

Thanks for the safety tip though.