FallDownGoBoom

My Feedback: (1)

Once you've made it this far, the rest is easy. Very carefully and neatly cut the sheeting over gap between the retract rails, put the retract body where it needs to be, drill the screw holes, and sand out an opening for the spring loop in the strut. Before I did all the sheeting, I also put another styrofoam block between ribs W3 and W4 to support the sheeting. You could also use some of the expanding urethane foam to do this. I also put small pieces of scap balsa between the sheeting and the top of the retract rails so that the sheeting doesn't wiggle around.

I lined the interior of the retract opening with 1/32" balsa so that everything looked neat. At this point things looked like this.

I'll finish the story of the installation tomorrow, as well as add the infamous "... if I had it to do over ..." section.

MinnFlyer

My Feedback: (4)

In the future, you can just tack-glue the retract to the rails before installing them (I guess I should have mentioned that)

Also, I still don't quite understand why you made the retract rails so long?

FallDownGoBoom

My Feedback: (1)

Their length comes partly from my tendency to over-engineer everything. The other part probably comes from having seen the landing gear mounting blocks on my Venture 60 and miniShowtime, as well as some other folks aircraft, separate from the fuselage on "normal" landings. Our field is fairly rough, so I was concerned about speading the stress generated when landing over a larger amount of surface area. That's why I used 1/2" ply, and created a fair amount of glueing surface with the doublers and additional ribs.

If (when?) I was to build another, I think there would be adequate support if I made the rails out of of 3/8" play, and just created rib doublers out of 1/4" play that went on the outboard side of W4 and the inboard side of W5.

MinnFlyer

My Feedback: (4)

When I moved to MN 17 years ago, I had to start flying from rough grass. One of my dilemmas was that I kept ripping the gear out of my US40. I found that Robostruts provided enough shock absorption to prevent that.

They're pricey, but they work!

FallDownGoBoom

My Feedback: (1)

Here's the finished product. I used 6x3/4" socket head sheet metal screws to hold everything down.

When I first installed the retracts using my DX7/AR7010 flight set up, they didn't work consistantly. Sometimes they'd go up (or down), sometimes all I'd hear was a "thunk" from the microswitches, and sometimes one side would work and the other wouldn't do a thing. But if I took them out of the plane and hooked them up to an old 72Mhz test system I use, they'd work fine. So I'm thinking the problem's in the retact switch on my DX7, or a faulty receiver channel, or ??? I finally figured out they weren't working because the end-point adjustment on the retract chanel in the DX7 wasn't set to +100 and -100%. I corrected that, they tested perfectly, so back in the wing they go. I flip the switch, and all I hear is the motors straining, and one of them coming up to about a 45* angle. At which point multiple four letter words were used .

After a bit, I figured out the strut coil was rubbing on the retract rail, and that the 1/32" balsa lining I'd put between the top sheeting and the rails was rubbing on the outside of the retract body. These relatively small amounts of friction were enough to stall the electric motors. With a little sanding and cutting, adequate clearance was obtained and, at least to this point, they're 100% operational

FallDownGoBoom

My Feedback: (1)

A few thoughts:

1) As was said above, I think you could get away with using 3/8" ply for the rails, and shortening them up a little, as long as you made sure the W4 and W5 ribs were properly reinforced.

2) The retracts pull about 0.9amp in normal operation, and will draw about 2amps if they stall. There's some kind of timer in the micro-switch, so they only pull maximum current for about 5 seconds, then go back to idle current. But your flight battery needs to be able to deliver that much current without experiencing a voltage drop. I didn't notice any difference in their operation on when using 6V or 4.8V systems.

3) Make sure there's no binding in their operation. The motors have enough torque to get the wheels and structs up and down, but don't appear to have enough power to overcome any additional friction.

4) The included struts are 5mm in diameter, slightly larger than 3/16" music wire. But I don't think the Eflite steel is as strong as music wire. When I cut them to the proper length, my Dremel seemed to go through them easier than through a piece of music wire. And there was a slight bend in one of the struts after my first (and so far, only) landing.

5) I think Mike's idea of using Robostruts in combination with the retracts is a good idea. Which means you have to drill a 5mm hole in one of the Robart bushings, or void the Eflite warranty by drilling a 3/8" hole in the retract block. What would really be nice is if Eflite offered the retracts with an option for direct mounting 3/8" struts.

I hope all of this has been helpful if you're thinking about putting electrical retracts in an US, or for that matter, anything like a P47 or P51 where the gear retract sideways.

MinnFlyer

My Feedback: (4)

There is a way you can have a second battery back dedicated to just the retracts. I forget how to do it but does anyone out there have that schematic?

I'd like to see a diagram to run two retracts (or two servos) from a dedicated battery pack.

FallDownGoBoom

My Feedback: (1)

I'd draw up the circuit, but my drawing program is on my other computer and my home network isn't working today... so a verbal description for now. I'll assume (always dangerous) that we're talking about standard NiXX batteries with standard 3 wire servo plugs, and that proper polarity and continuity is observed.

We have to build a female/female jumper that goes between the male plug coming from the retract battery and the male plug on the end of the retract "Y" connector. Step one is to take a couple of 4" servo extensions, cut them in the middle, the set the male ends aside for the moment. Take the female ends and solder the red wires (+voltage) together, then the black wires (-voltage) together. Leave the orange wires (signal voltage) unconnected for the moment.

Next take one of the male ends from the operation above, and put heat shrink tubing over each of the red/black wires so they don't inadvertently short circuit. (They carry +/-voltage from the receiver, which we're not going to use.) Now solder the orange wire form this extension to one of the orange wires on the female/female jumper (it doesn't matter which). Put heat shrink over the other orange wire.

So we end up with a funky Y connector: a female end with two wires that goes to the retract battery pack for power; a male end with one wire that plugs into the receiver's retract port for signal; and a female end with three wires that connects to the retract Y.

Once every thing's plugged in, it provides power from the retract pack directly to the retracts, and signal voltage from the receiver. And no, I haven't tested this... but I think it'll will work.

JNorton

My Feedback: (2)

The concept might be more easy to explain and grasp than a word description of each individual wire. Basically you use a common ground between all batteries, servos and the receiver. The individually powered servos use their own battery, the negative connected to the common ground, the positive to the servo split off from the receiver. The signal lead from the receiver goes to all the servos. Hope that makes sense.
John

MinnFlyer

My Feedback: (4)

I'll wait till I see a diagram [&:]

FallDownGoBoom

My Feedback: (1)

My illustration skills are not equal to yours, Mike. So my pictures aren't worth 1000 words

I left out switches between the batteries and the receiver and the Y connect, and also didn't label +/- voltage wires. But this should give us a rough idea of how the circuits should work.

MinnFlyer

My Feedback: (4)

Gotcha! It's perfect.

FallDownGoBoom

My Feedback: (1)

I'm not sure if this meets John's idea of using a common ground. But I just figured the signal wire needed some form of negative connections, which should be supplied by the retract battery.

JNorton

My Feedback: (2)

The common negative rail is inside the receiver. All the negatives leads are connected togther anytime you plug into the receiver. I did misspeak however - the signal lead - is opposite the negative or ground wire, you show it as orange. The positive wire is in the center - just as you have shown. Your first diagram is confusing. Your second diagram on how you wired it is correct except the black wire you show as taped off should be connected to the other black wires. This provides a signal path back to the receiver for the servo signal control wire.
John

JNorton

My Feedback: (2)

It's easiest to understand if you just use one servo. You need the negative or common return for the signal return to the receiver. Otherwsie you only have the signal wire alone going to the retract servo. There is no path back to the receiver for the signal pulse to operate.
John

FallDownGoBoom

My Feedback: (1)

John,

I understand what you're saying, at least to some extent. In simplest terms, as wired there's no return signal path for the orange wire to the receiver. I keep thinking I'm gonna have to go spend $8 for a couple of servo extensions and try this for real

But if we do that, doesn't it also open a path for the positive current from the retract pack back to the receiver? Which would, in effect, result in dual batteries wired into the receiver?

JNorton

My Feedback: (2)

For the signal loop you do have current flow fron the receiver battery, but the motor load comes from the auxillary battery. Trust me on this.
John

MinnFlyer

My Feedback: (4)

So... Like this?

JNorton

My Feedback: (2)

Exactly.
John

FallDownGoBoom

My Feedback: (1)

Nice drawing, Mike. This might be the most valuable piece of knowledge to come out of this thread.

MinnFlyer

My Feedback: (4)

Thanks. I think I'm going to try this on my next US60. I picked up a cheap pair of electric retracts that seem to work well. But I'll plan to switch back to my mechanicals just in case!

JNorton

My Feedback: (2)

Fred,
Do you have the part number for the H9 retracts you are using. I really wanted a set of Minn's mechanical retracts but finances were tight. By the time I had the money they were off the market. Money's still tight but hopefully I can sneak in a pair by spring.
John

MinnFlyer

My Feedback: (4)

If any of you guys are machinists, I'd be happy to share the design of my retracts

They require a CNC milling machine, but the design can be dummied-down for a standard mill

JNorton

My Feedback: (2)

Minn,
I'm not but one of the guys in the plant owes me some favors! PM me and I'll send you my email.
Thanks,
John

FallDownGoBoom

My Feedback: (1)

John:

The part number on the electrics is EFLG400 60-120 90* electric retracts, listed at $149.99. Maybe your LHS might make a deal.

Thanks for the electric help... nice to know that the electrons will go where they're supposed to.