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Hydraulic Retracts

Old 02-13-2014, 08:43 AM
  #51  
Jgwright
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Vin

Yes the switch is on when the servo switch is on. In my case the servo switch is controlled with a manual servo controller and left in an on position. The pressure switch will be on until it reaches pressure and switches off. (There is a small deadband pressure area.) The servo that controls the Eurokit valve then acts much like a pneumatic system. As soon as it switches over the pressure falls and the pump switches on until the set pressure is reached, raising or lowering the retracts. The pressure is held by the non return valve positioned on the supply to the valve before the branch to the pressure switch. (see my first photo).

I could always use a second channel to power up the pump rather than using the manual servo.

John
Old 02-16-2014, 01:58 AM
  #52  
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Default Retracts

Great project John, well done, I might even have a dabble myself if I can dig out a spare set of pneumatics. I've had quite a lot of success with electric retracts on my Flash for maybe 2 years now, been pretty much fit and forget.

Latest slow burner is the Tutor, not sure I will ever get it finished but it's been fun so far getting the the landing gear all electric.

Great project John, well done, I might even have a dabble myself if I can dig out a spare set of pneumatics. I've had quite a lot of success with electric retracts on my Flash for maybe 2 years now, been pretty much fit and forget.

Latest slow burner is the Tutor, not sure I will ever get it finished but it's been fun so far getting the the landing gear all electric.

http://youtu.be/CDnOpZnu7wo

Rob.

Rob.

Last edited by Robrow; 02-16-2014 at 02:10 AM.
Old 02-16-2014, 08:53 AM
  #53  
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Originally Posted by Jgwright
Mike the switch I selected was the GEMS PS61-19-4MGZ-B-SP
http://uk.rs-online.com/web/p/pressu...tches/7794238/
They are cheaper than buying a cylinder but are heavy. They call them subminiature, hardly a term I would use! I have checked it with the pressure gauge and adjusted the switch point. Seems to work well. Unfortunately the BSP converter to 4mm push fit had the wrong thread on it so I very careful drilled out the hole to 4.2mm and tapped M5. I drilled and tapped it horizontally so there was little chance of bits dropping into it, and made sure to tap it on the bench first before having a look. My test was with the continuity test meter but I have no reason to think it will not work substituting it for the cylinder and micro switch.



John
John,

I'm surprised that you haven't already chucked that switch in the lathe and taken off some of that extra weight! I looks like the main body could be rounded off and the threads on the end smoothed out if you are not panel mounting it. Then put a purple label on it, triple the price and call it.......uh never mind

Tailwinds,

John
Old 02-16-2014, 09:16 AM
  #54  
Jgwright
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John

Yes If I knew the internal layout I would have attacked it! It would be easy to lose 20 grams, maybe more. I resisted the temptation and will test it first.

John
Old 02-17-2014, 06:49 AM
  #55  
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Rob thanks for the kind remarks. I would recommend using hydraulic if they are large wheels with doors that have a big drag from the air stream. The only downside is the mess when playing with them!

I have now had a chance to test the UMS system.


My findings are


1) the top up tank is nice small and light with good seal and good fittings.
2) the electronics I do not like. The system on smallest setting does not seem to switch off so must be very high pressure.
3) the valve is fine, but had barb connectors as opposed to the Eurokit one which has nice push fit connectors, the valve did not leak.
4) The motor as some report gets hot quickly and in comparison with the very small Xicoy unit does not push the oil as efficiently


I am grateful to David Gladwin for sending it to test.


I have also tested the GEMS pressure switch and that works fine except it has a very small deadband and the slightest fall in pressure kicks the pump back into life. It tends to sit there twitching every few seconds. That would not be a problem if the pump actuates as part of the sequence for landing gear. I am inclined to use the switch in the plane as it is a little neater and easier to install than the cylinder. I did wonder about using a tank pressure switch that has a bigger deadband but not sure if it would stand up to the hydraulic fluid.


I tried the UMS pump with the pressure switch and it dies not seem to switch off easily as it leaks past the gears so much and twitches for longer than with the Xicoy one.


John
Old 02-21-2014, 05:16 AM
  #56  
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Hi John,

Thanks to you and Mik for showing such a simple and reliable hydraulic system.

A quick question regarding the drilling of the Robart cylinder: did you use a 3mm thread or a 5mm thread for the 4mm Festo connector? I assume it's quite critical as a 3mm thread may restrict the flow but I may be wrong?

Many thanks again.

Roy
Old 02-21-2014, 07:31 AM
  #57  
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John,
With out any gauges how did you determine the spring size/tension you are using in the robart cylinder?? I have a UMS system coming and plan on setting up a gear test on my bench but I would like to add the accumulater to the system. Where did you get the xicoy pump?? would a jetcat fuel pump work too??
Thanks,
Vin...
Old 02-21-2014, 09:24 AM
  #58  
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Originally Posted by Roy Hanouka
Hi John,

Thanks to you and Mik for showing such a simple and reliable hydraulic system.

A quick question regarding the drilling of the Robart cylinder: did you use a 3mm thread or a 5mm thread for the 4mm Festo connector? I assume it's quite critical as a 3mm thread may restrict the flow but I may be wrong?

Many thanks again.

Roy
Roy

I would use a Festo 4mm fitting with a 5mm thread if there is room, if not use the Festo 4mm fitting with the 3mm thread. The hole through the thread is only short so does not affect the flow too much. On my retracts I used one with a M3 thread and one with a M5 thread on each cylinder. The key thing is to use 4mm tube.

John
Old 02-21-2014, 09:33 AM
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Jgwright
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Originally Posted by Vincent
John,
With out any gauges how did you determine the spring size/tension you are using in the robart cylinder?? I have a UMS system coming and plan on setting up a gear test on my bench but I would like to add the accumulater to the system. Where did you get the xicoy pump?? would a jetcat fuel pump work too??
Thanks,
Vin...
Vin

I tested the cylinder with its spring before filling it with fluid. I just used the normal air pump with its gauge to determine the psi I wanted to retract the gear. If you use a GEMS adjustable switch it is very simple to increase the pressure after it is filled if you find that you have set it too low. These switches are cheap and work well. I prefer them to the cylinder, but by all means have a play with using a cylinder. The only thing you will need from the UMS system will be the valve. The Xicoy pump is available from

http://www.xicoy.com/catalog/product...roducts_id=240

I guess that the Hausl pumps that Jetcat use would work just as well. I would try it and see how it works. The UMS one has a 'leaky' action and is not anywhere near as positive as the turbine fuel pumps. I only need a 2 cell 1100 may A123 pack for a number of cycles.

Do make sure that you use the stronger pipe though. Let us know how you get on.

John
Old 02-21-2014, 09:43 AM
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Thank you John.
Old 02-21-2014, 10:11 AM
  #61  
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I really don't want to use the cylinder but your testing on the Gems indicated that it might be a little to finicky for this application??
Vin...
Old 02-26-2014, 05:49 AM
  #62  
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Hi John,

Another question regarding the high pressures and the Festo tubing:

You and Mik are using heavy-duty 4mm Festo tubing to handle the pressures.

Mik is using 3mm Festo tubing on his gear doors and rams. Not sure if you are too, but there seems to not be any heavy-duty 3mm OD Festo tubing. Wouldn't standard tubing burst under the pressures your system is running at??

Roy
Old 02-26-2014, 06:14 AM
  #63  
Jgwright
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Roy

No I am not using hydraulics for the door rams. I shall probably use air as they are not normally a problem.

http://www.airlines-pneumatics.co.uk...Code=S08000105

This site has Nylon 3mm tube for up to 55 bars pressure.

John
Old 02-26-2014, 07:40 AM
  #64  
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Thanks so much John. That would work perfectly.
Old 03-15-2014, 12:37 PM
  #65  
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Were to you order this valve? I want to replace the one that came with my conversion, and anywhere in the usa to order the PAN-R tubing?:

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Old 03-15-2014, 11:24 PM
  #66  
Jgwright
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Yes this is the correct valve. They come with 4mm fittings built in and do not appear to have leak problems. I saw your photos on the F15 thread. Looking good. You will be pleased with the results when you have it operating. If you look for nylon tube 4 mm dia you should find a supplier. You will need to check the specs but you should find it will be adequate. Good luck!

john
Old 03-15-2014, 11:37 PM
  #67  
Jgwright
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I see that smc do a 4 mm nylon tube with 220 psi rating which should be ok. You should find a local smc stockist.

John
Old 03-16-2014, 06:11 AM
  #68  
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Allied electronics has this I'm using this on 4mm nylon on my f-18 conversion.

NOTE ITS not the easiest tubing to work with if you are using to poly ureathane you will will be a little annoyed.
Old 03-16-2014, 06:48 AM
  #69  
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Frank;McMaster-Carr out of Chicago carries what your looking for,I am using a ums system on 1/4 AD-1 skyraider and have had no problems yet.George.
Old 03-16-2014, 09:14 AM
  #70  
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McMaster Carr carries that valve? I found a place in NJ to order the Pan-R tubing.

http://www.plccenter.com/en-US/Buy/F...LECTRIC/541674
Old 03-17-2014, 07:02 AM
  #71  
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I"m having huge issues with my setup, the ums tech setup and pump can't even lift 1 retract on my 1/6 F-18 :/ motor seems to be cooking it self trying to lift also there appears to be a lot of pressure being built up Not sure what is going on. Does anyone have instructions on the UMS tech kit I need to make sure I have these setup correctly.
Old 03-17-2014, 07:31 AM
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I would ditch the UMS electronics and use a Battleswitch to turn the pump on

http://www.dimensionengineering.com/...ch-diagram.jpg

You will need a non return valve just before it feeds the valve.

I am now using the GEMS PS61-19-4MGZ-B-SP pressure switch to control the hydraulic pressure generated. This is wired into the negative wire of the servo line to the Battleswitch.
You need to check the pressure it switches at before installation. Mine came at the max setting 275 psi so I reduced it to around 150 psi. 'You will be fishing in the dark' if you are not checking the pressure of the switch point.
With your UMS system you need to fit a gauge to check the pressure.

I tried the UMS pump and frankly it was nowhere near as good as a standard turbine kero pump for an engine of 100n or more.

I would be amazed if the retracts failed to work at all with hydraulics. You will need to bleed the air from the lines to get it to work well.


John
Old 03-18-2014, 03:04 AM
  #73  
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John,

I have been following up on the hydraulic retract systems and i am very interested to get into a reliable setup. the main problem is that information on the subject, even in a same thread are a bit unclear (at least for me, no one is to be blamed).
I would be very grateful if you could find the time (at your convenience) to provide a recap of the different components you have to get to achieve a hydraulic system, in addition to source for getting each part.
This could be used as a working manual for many who i am sure would be interested to switch to this mod.

Thanks in advance,
Regards,
Dany
Old 03-18-2014, 08:37 AM
  #74  
Jgwright
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Dany


The whole thing about Hydraulic conversions is that they are really quite simple to get to work well. You do not need an expensive 'system'. Think of it as a liquid based pneumatic system with a few extra items.


Ok here is a list


You need:-


1) a means of getting pressure i.e. a pump. Standard kero pumps work well except for the very small Flightworks one.
http://www.xicoy.com/catalog/product...roducts_id=237
2) A means of limiting the amount of pressure. An accumulator system as Mick uses made from an old cylinder with a spring fitted on one side that operates a micro switch OR a pressure limit switch like the GEMS PS61-19-4MGZ-B-SP (this is fitted in the negative line of the servo lead to the servo switch. The pressure switch will need tapping M5 and fitted with a Festo M4 fitting
http://uk.rs-online.com/web/p/pressu...tches/7794238/
3) A servo operated switch like the Battleswitch that turns the pump on
http://www.dimensionengineering.com/...ch-diagram.jpg
http://www.lipoly.de/index.php?main_...d=Battleswitch
4) High pressure 4mm od pipe. Use Festo special tube or Nylon that will stand 225 psi is required for all lines.
http://www.kiowa.co.uk/Festo-PAN-R
5) A valve, the Eurokits one is best but the UMS one is also ok. It is available separately. (The valve is operated with a servo the same way as a pneumatic system.)
http://www.airfighter.eu/Fahrwerke/e...aulics/Eurokit
6) An oil reservoir tank, the UMS one is good and has a nice O ring seal.
http://www.hobbyking.com/hobbyking/s...etracts_.html7) The retract cylinders need tapping M5 and fitting with Festo 4mm fittings
http://www.kiowa.co.uk/products/QSML...P00016769/1008
8) The Incoming line to the valve needs a M4 Festo non return or check valve (this is a spring loaded ball inside the fitting)
http://alshobbies.com/shop/cat.php?i...=21&NumShow=20
9) Oil, I used Citroen hydraulic LMM+ fluid.
http://www.ebay.co.uk/itm/like/28101...d=604521252137
10) Battery to power the pump, I used a small 1100 mAh A123 2 cell pack, but a small Lipo would also do.


The connections are simple just as you would of pneumatics except you need the pump, the pressure limiter and the one way valve on the line into the valve. It can be a bit messy when you first put the system together so keep plenty of paper towels handy. Just be aware if you undo a Festo with the system under pressure it will squirt oil out. You will soon get the hang of how to bleed the system and should be very pleased with the results.


If you use an electronic sequencer or a Powerbox Cockpit SRS you should be able to switch the pump as part of the retract cycle rather than leaving it on all the time at the flying field.
Hope this all helps.


John

Last edited by Jgwright; 03-18-2014 at 02:20 PM.
Old 03-18-2014, 09:44 AM
  #75  
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John,

That's fantastic - thank you. I'm planning on a hydraulic system for a Tomahawk-Design Hawk. Would I be right in thinking that the specifications you gave will be sufficient for a landing gear of that size?

Thanks again

Bob

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