If you are having trouble with the 60-120 retracts, check the current draw. If the gear mechanism binds, it can get quite high, (1-1/2A or so). The normal current draw with the gear in motion (without wheels) is about 300-500ma with both main gears in transit. The highest peak draw seems to occur when the gear is just starting from the retracted position. There is a current protect circuit that trips when the current draw is to high for too long. I'd go along with the idea of using a power source other than that used for the receiver and flight servos. If you have high current draw, try loosing the three screws that hold things together. If this helps, it may be that the side plates are too close together, slightly misaligned, or the brass rod shuttle is binding on the side plates and/or the gear fork.
Light lubrication may help.

Thanks. I have now done further tests:

Using a DVM (which averages readings over a 1/2 second or so and accordingly does not show spikes, which might trigger problems) and with 7" legs and wheels weighing about 4.4 ounces

On 4 cells 4.8volts

Operating current for two legs - up to 0.8 amps.

Voltage at battery drops to 4.8v, presumably less at the units.

Stall one or the other - up to 2 Amps for a few seconds, while buzzing followed by tripping off.

Voltage drops to 4.2 volts, enough to trigger throttle failsafe to slow and perhaps stop coded signals getting through.

One wheel or both will fail to operate about 1 time in 5.

Simply touching a small screw - no force, just touch - on one of the mounting flanges will trigger a down/up cycle - sometimes but not always.

The margin between just about operating normally and tripping off is TINY - slightest touch with a finger against a wheel will cause it to trip, so nothing whatever in reserve.

On the worst unit there are clearly 3 tight spots along the movement, most logically due to thread imperfections.


5 Cell 6 volts

Contrary to suggestions, more voltage does not prevent these problems.


As things stand I am undeciced about whether to return and demand my money back as unfit for purpose, or to hope these are just bad units and replacements might work or strip out the badly designs parts and use the basics using servo operation.


I note that the guarantee - not visible until the box has been opened of course - says it is limited to repair or replacement. I do not know whether they can get away with that under US law, but they certainly can not under British law which requires that products do what they are supposed to do, for a reaonable time, and are fit for purpose.


On balance at present I think that these units are so badly designed as to be unfit for purpose, that replacements would also be and that I should stop wasting time and money on them

yeah sorry you'recorrect, its a lead screw mechanism but as you rightly say the principal is the same.
I'm following this thread closely because I just bought a set of the 85 degree 60 - 120 size units.
If these behave similarly to yours it will be the 8th HH product I've biught that has turned out to be a lemon. Cross fingers!

Thanks. A friend here in the UK has just told me he saw someone using an E flite retract in an electric model this evening - one leg hanging down!

I have just cleaned and re-worked my 30 year old all metal retracts, with longer (7") legs and 3" wheels. At present a 17 kg cm servo only just manages to lift the legs, despite a helper sptings build in. On the other hand, stall current is only 250 mA so no electronic trip needed, or there to cause other problems.

And it lifts them in half the tme.

The torque of 2 wheels trying to fall out of the wells is about 2 kg cm so as yet not clear why 17kg cm servo is struggling - I must look more cloaely at the geometry and particularly anything that slides to generate friction.

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 may disagree, and I have no commercial reasons whatever 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

Here's what seems to happen with the E-Flite electric retracts.
There is a curved slot cut into the side brackets. At each end of the slot is a pocket that a brass "T" rests in at the end of travel.
To go from the pocket to the main part of the slot, the brass "T" goes over a sharp transition. This seems to be the high current portion of the travel with the electric retract gear unloaded (No wheels, just the struts.) If the gear draws too much current for too long, the protect circuits in the gear "trip". The total current draw at the transition easily exceeds the 900ma listed in the gear specs. (Even after going thru all sorts of gyrations to minimize friction, interference, etc.)
When you look at the peak current draw, it's enough to cause a four or five cell receiver pack to significantly drop in voltage output, likely to a voltage that is marginal. (Somewhere below 4.0 volts.) You also have to consider that the battery may not be fully charged, which further increases the voltage drop under significant load. If the battery pack is at 50% charge or less, the voltage drop is really significant under load!

Separate battery packs or a separate good current capable BEC seem to be in order. Additional capacitors might help lower the peak current needed from the battery or BEC.

Thanks for your confirmation of one of the problems I found, but there are many more. My detailed summary if the retract and connector problems is too long to post 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/m_10...m.htm#10550716

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

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

Another fix for equipment that spikes the demand is to increase battery capacity. WingSpan came up with that advice early on in their marketing when so many of their retracts had problems. They advised the use of something like 1500 mAh packs in models that had a history of 600 pack usage. Increasing voltage gets you more power, but more capacity backs that up with even more. The choice of chemistry also plays in this. I found that NiCd packs of equal capacity to NiMH actually performed better when I was trying to get my WingSpans to move the same gear Lados had no trouble with. LiFes were found to beat 'em all in about all respects.

Sorry for duplicated posting.

I agree with the Chukk2 analysis, wich I missed last time - it confirms one aspect of my findings of friction high spots due to inadequate clearances and other problems, including inadquate spacing between the frames. See my web site comment for full details.

In my view higher voltage and higher capacity and better battery chemistry do no more than mask the problems arising from a the original decision to use a lead-screw, and all the electronic, electrical and mecchanical problems that follow directly from that decision and that very poor efficiency, which leaves no margin to overcome even minor resistance and which in turn leads to current limits tripping and setting of unwanted cycles.

If I had the job of fixing the design, and I found as I suspect that plastic thread followers that would reduce friction substantially would not take the loads in those small sizes, all that remains available is elimination of the lead-screw geometry - perhaps by using a motor with its axis from wingtip to wingtip, driving at some stage in its overall reduction a bevel gear to translate rotation into the other plane.

But I am not in that position nor do I have the time or equipment to experiment, so I found it much easier to ditch the drive system altogether and fit a servo to each. Simple, reliable, does nto need an extra battery due to acceptably low current even if stalled. And lots of reserve torque.

No probelm, RCU has lots of storage space. (and grubbins to edit dupes)



Got a picture or two? I'd like to salvage the two sets I've got somehow.

Sure - there should be a few on my camera I was about to knock off early (12.15am) foran early start at the Hants field near Stockbridge or Beulieu, but I will spend a few minutees putting the .jpg files on my web site, accessible at rhe bottom of the page at http://www.fightbackwithfacts.com/re...ctor-problems/.

Ihave 4 sets of these 60-120 retracts in all war birds, even a Hanger 9 B25

But in my nitro planes 72in BF109 with a 35cc motor, my left landing gear keeps going down while im flying around. its not messing with my flights and it alwasy stays down wiht the other for landing. But its odd as it gos up and down durning the flight not matter what motor speed or moves.

Any ideals?

Thanks Mike

I'm not quite sure how the electronics decides what the UC should do, but it does seem to me that rather than following directly the up or down order from the Tx/Rx it takes its orders from a bip-stable circuit of some kind. that can only be triggered into telling it to go UP when it is in the DOWN position - and vice versa.

This seems to be why neither UC will reverse direction part-way, and once it has been triggered to move by something, in error, it has to complete the cycle rather than suffering a brief g;itch out of position.

I see this as a further problem, if near the ground, because of the time a complete cycle can take. In other words what would otherwise be a brief glitch away from the DOWN position in preparation for landing, becomes 2 or 3 seconds not locked up or down. I suspect that any touch-down when not in the locked position, imposing side loads on the leg, would do the leadsrew no good at all.

In your particular case my guess is that something is triggering the bistable circuit in that unit to the DOWN position. As I have commented here, even just touching a screwdriver lightly on the frame could be enough to trigger that one, or just as likely the other one, into cycling. I would be tempted to look for metal-to-metal noise in the offending unit or nearby. and to try eliminating it by attaching short flexible leads to any parts that might be rattliing. Or the frames to battery negative perhaps.

Others have confirmed my findings of "high spots" in the movement where the precise nature of the rubbing parfts at that point in the travel causes the current draw to rise above normal, and as we know that can trip the current overload circuit. I would therefore also look for tight spots in the moving parts, as reported here and on the other web sites I identified above, e.g. the sharp corner between locking slot and transition slot, or inadequte sideways clearance (easily checked by slackening the locking screws to see if the movement frees up. My view is that if having the screws properly tight tends to make the movement jam, the right answer is NOT to fly with the screws slack, but to fit whatever thin shims are needed between the spacers and the frames to provide proper clearance with the screws tight.

Incidentally, the photos of my servo adaptation are now in place on my web site.




But as I say, I am only guessing.

  Well to all that have been following this thread ,, I've started having trouble with my retracts too .   I first started with them powering up off the flight battery, that was ok for a little while then they started stalling on me and using a l;ot of juice ... Now I have them hooked up to a deducated power supply with a 6v life battery .   Got wiring diagram from this thread . But one side would fail to cycle  only about about once in 6 trys .. When it was mounted in the plane , it was very sporadic, take it out and it worked  every time . It was detrimined that there was a slight shift in the retract  to cause it not to cycle .  I put a 5/32 washer under the 2 screws closest to the wheel . This let it shift , but not shut off .  now they work ... if they don't I'll post up ..

5/32 or 157 thou, or half that as at only one end, ie 88 thou, seems a lot of clearance to me - would have thought 1/10 of that would have been enough.

Regardless of that, this further report confirms that the tolerances are not being maintained adequately in manufacture, clearances are disappearing.

With an efficient drive train the stiffness would not matter that much but the leadscrew inefficieny makes evertything marginal.

By coincidence I met one of the contributors to the similar discussion on the UK web site I mentioned - he found that removing the sharp corner in the milled slots in the frames cut maximum current by 50%