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Old Jun 01, 2012, 04:59 PM
UH-1 Gunship, AH-1G jock 69-71
makeitworst's Avatar
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Help!
Testing Servo-less Retract Landing Gears safely

I just received a bunch of 3.7g Servo-less Retract Landing Gears from, where else, China. These are pretty high quality, rebuildable, metal gears, metal strut block. I'd like to test them in a simple way just for operation - opening / closing repeatedly - before installing them. I'm pretty new to servo-less retracts, always used servo or air-operating retracts.

Looking for suggestions on how to set up a "test rig" without using a transmitter to test them without damaging or burning them up. I have a 3 Mode Servo Driver / Tester (see picture) that has 1) Manual mode, 2) Auto Neutral centering, and 3) Auto Continuous Cycle (rotation) mode. This Servo Driver connects to an ESC and then to a LiPO for power.

I would like to test full extension to retract, lock up and cycle the retracts (open / close) to filter out the flaky ones, if there are any.

Any solid suggestions appreciated.
Thanks
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Old Jun 01, 2012, 08:12 PM
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Don't see why this would not work.
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Old Jun 02, 2012, 08:30 PM
UH-1 Gunship, AH-1G jock 69-71
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Conventional Servo Tester not an option.

Just an update, tried the Servo Driver / Tester I have and did not work to drive the eRetracts in any mode. I'm thinking the pulse (cycle) signal rate from the tester does not match what an Rx and Tx uses to signal the servo-less eRetract to open / close.

Still looking for options.
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Old Jun 02, 2012, 09:11 PM
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Have you tried a servo to see if the unit is even functioning? It should work if the signal flips either side of neutral.

Same with plugging each retract into the Rx gear channel. Ensure each unit works separately before finding fault with the tester.
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Old Jun 03, 2012, 03:54 PM
UH-1 Gunship, AH-1G jock 69-71
makeitworst's Avatar
So Cal ... Kingdom of Taxes
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Quote:
Originally Posted by Cougar429 View Post
Have you tried a servo to see if the unit is even functioning? It should work if the signal flips either side of neutral.

Same with plugging each retract into the Rx gear channel. Ensure each unit works separately before finding fault with the tester.
I had the same thought, even though I often use the Servo Driver /Tester to center the servo and to test suspicious ones; but I did grab a servo I know works and the Servo Driver does "run" the servo.

I'm now wondering if these Servo-less Retracts are "Digital", while I know the Servo Driver/Tester is definitely analog?
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Old Jun 05, 2012, 10:11 PM
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I use a hitec servo tester. I also have the 120 sized eflight retracts. The cycle time on the retract would take longer than the cycle time on the servo tester. There would need to be about a 4 second delay, better at 5 seconds to let it lock good and sturdy and hold before changing.
Edwin
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Old Jun 06, 2012, 01:13 PM
UH-1 Gunship, AH-1G jock 69-71
makeitworst's Avatar
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Quote:
Originally Posted by edwin1 View Post
I use a hitec servo tester. I also have the 120 sized eflight retracts. The cycle time on the retract would take longer than the cycle time on the servo tester. There would need to be about a 4 second delay, better at 5 seconds to let it lock good and sturdy and hold before changing.
Edwin
I'm not familiar with the E-Flite retracts at all, perhaps their method of operation is different than the ones I have, using a circuitry much more like conventional servo to drive the gears up and down.

Here's what I am gathering researching this furiously on the web and writing some well known online RC parts sellers who been around the block in RC for some time. Randy Moore at RC Dude gave some particularly good insight on this topic. If the common "eRetracts" (external servo-less) operate the same way the traditional "retract specific servos", like Futaba, Airtronics and Hitech have sold for years, then they only need a single pulse signal to tell them to Open or Close in one continuous operation (all you have to do is watch one operate to see this. I did on several of my older planes using Retract Servos made by Futaba) - NO incremental steps like Aileron etc. Servos work. This would explain why my "regular" servo Driver / Tester doesn't work - doesn't send the right kind of signal pulse a Retract Servo expects or can interpret.

Now that's not saying that some "eRetract" brands are using a regular servo type circuit, perhaps your E-Flites are this type. Of course it stands to reason then with this type eRetract runs the danger to stopping somewhere BEFORE it's fully extended and locked, which the other types can't do.

So, that's my theory on the eRetracts I have, at least. The book is still open for any potential re-writes on the theory. Still looking for conclusive evidence.
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Old Jun 06, 2012, 01:31 PM
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My experiments with the eflights showed that they transition either side of neutral. I can take my hitec servo tester and swing just a bit either side of neutral to get the retracts to cycle. You're correct about retract servos, they just look for a difference from a given setting (full + or full -), such as you would see on a switched channel generally used on a retract channel. I cant just pulse the retract channel to get it to change and stay changed.
I have found that I can confuse the eflights by switching rapidly and get them to hang. Not a normal environment, but cycling power off then back on resets it.
Edwin
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Old Sep 24, 2012, 10:10 PM
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My experience with the E-Flite 60-120 retracts was that two different sets required much more instantaneous current than the specs indicate. The maximum draw occurs as the gear starts to extend or retract, and the brass slider rides over a sharp point in the side cam slot.
A four cell NMIH or NiCad at full charge works marginally. At 50% charge, the gear operation is erratic, due to battery voltage drop under load. With the 2400mah NMIH I used for test, at 50% charge, the voltage drop was enough to cause a Spectrum AR600 to see a momentary voltage dropout, which was indicated by a receiver LED blink. Looking at the voltage vs discharge current graphs for the NMIH and NiCads, it looks like 1 to 1 1/2 A is the capability without excessive voltage drop for AA size cells at less than full charge.
It's possible to reduce the current draw with lubrication, Side plate realignment, and slightly rounding the sharp points of the cam slots. Turning the brass cylinder 1/2 turn on the lead screw may also help (or not) the current draw slightly. If the battery voltage is low enough, the gear current sensor may trip due to stall current. This can cause such things as no operation, out of sync operation, or even partial operation. On the two sets we tested (out of the box), the gear would usually retract, but might not extend with a low battery condition. Power up should be done such that the gear can be cycled once or twice after TX/RX initialization is complete. (Handheld or stand) This allows the TX gear switch and the gear to sync properly.

When working properly, the gear electronics sense two pulse widths, one for extend, and one for retract. There is a fairly wide "dead band" between the pulse widths. Detection is a less than or greater than scheme. Gear transit is stopped by limit switches, or in case of a stall, by the current sensors.
I'm told that the actual peak current draw can be greater than 1 1/2 A. This is consistent with what I've seen on various testers, although they will under read peak current.

The retracts went into a Hanger 9 40 size P-51 Mustang ARF. A separate 6v 5A BEC was used to power just the retracts.
The P-51 is powered by an Eflite power 52, 6S 5000Mah battery, 12x6x3 APC propeller, and a 75A Castle speed control.
Peak power from the castle log is 1624W, just under the motor rating of 1650. Max current was ~68A
GPS speed 88Mph. ~2.2Hp

New gear doors were fabricated, due to differences between the E-Flite and Robart retracts. Some shimming at the gear mounts was needed to pitch
the gear slightly to the front, and allow the gear legs to center in the slots cut with the furnished template. The template also needs to be adjusted for the gear leg springs, as they are positioned closer to the retract mechanism on the E-Flite electric retracts.
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Old Nov 17, 2012, 09:46 AM
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testing the test

I've found that I can get myself to a dead end if I create a test that winds up more elaborate than the base situation itself. I think I'd find a battery pack, receiver, and transmitter with a 'retract' channel, that one's not proportional, as retracts aren't proportional either, and hook up the retracts to the receiver and give it a go. That's about as close as a bench test is going to get and exposes the retracts to its finished working environment.
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Old Nov 18, 2012, 11:23 AM
UH-1 Gunship, AH-1G jock 69-71
makeitworst's Avatar
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If you buy 10 or 20 eRetracts at a time to get a great price as I do, a semi permanent test bed is a better idea than having to tie up a perfectly good 7 or 8 channel (expensive) 2.3 Ghz receiver (since not many 5 or 6 ch RX have retracts and also your expensive radio.

But since there doesn't seems to be a servo tester I could find to work in a test bed, I did have to go with using an expensive RX. Oh well.
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Old Nov 25, 2012, 08:14 AM
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I still regularly set up my retracts with a servo tester similar to the one in your first pic. Never a problem. I use a 5 cell 1500 MAh NiMH pack for most of these tests.

The ONLY time I can see an issue is if the unit is set for servo sweep cycling, on mine the third option. In that case the signal may lead the retracts preventing them from having enough time to follow along before the signal reverses. This option is really not required for this type of application anyway as it was intended to break in servos by cycling them back and forth. In my unit the servo sweep seems to be reduced in that mode.

Perhaps you can experience problems if the current requirement is high with larger units and it is fed through the servo tester, but in that case I would feed battery power directly to the retracts with a Y-connector to get the battery and signal leads back to the OUTPUT of the servo tester to prevent any high current flowing through the unit. This would be identical to a receiver setup as you do not want high current flows through the power bus in a receiver.

However, if your retracts require high currents they are either huge units or there is some other problem. Either way I would recommend electrically isolating them from the rest of the system. On that note I have run everything up to Eflight 60-120 units through the tester. Just make sure I plug the battery into the output.
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Old Nov 25, 2012, 08:36 AM
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makeitworst,
Seems like a Hobby King orange clone would be good for that if you feel its necessary to use a receiver. Less than $10 in most cases.
Edwin
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Old Nov 26, 2012, 01:01 AM
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I just finished up-dating my blog with info on servo testers and E-Tracts.

Gary
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Old Dec 02, 2012, 04:47 AM
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Some servoless retracts can take around 10 seconds to operate the first time, then they work perfectly after that. Maybe they have a capacitor in them that needs to charge up for initial use. If I disconnect my Trojan ones it takes time after I reconnect before they operate.
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