Converting my old pneumatic retracts to electric.

[Flyinfool]

For those that do not know what a retractable landing gear looks like, This is what I am starting from. It is an old Robart 500 series main gear.
My goal is to replace the pneumatic cylinder with an electric motor/actuator. It is the aluminum cylinder and its shaft that I will need to replace with new parts. I will be making a new aluminum cylinder to the same outside dimensions but with the gear motor shown above inside of it. The threaded output shaft will need to be cut to length, I I will have to figure out a "nut" to ride on the thread and interface with the gear trunion while riding in that wavy slot in the side of the gear.

And yes I did manage to loose the Jesus clip that held that pin in place as it left the area at mach 2 as I was removing it. I even held my cupped hand over it and was working on a white towel so that it would not vanish. Of course it is made of beryllium copper and I never got around to buying a Beryllium copper magnet to aid in the search. It is really tiny Ø7/32 shaft and only a 0.012 cross section. New ones are in my McMaster cart waiting for more parts needed, otherwise the postage would be more than the parts. I know I will be needing some tooling and material for this job.

OK Back to the drawing board.......

This is the gear up position



This is the gear down position



Disassembled top view.



Disassembled side view.

 

[wachuko]

Please, lots of photos. Following

 

[Flyinfool]

Ran into first snag.
When the landing gear is in the DOWN position The shaft of the drive motor will hit the screw that clamps the gear leg to the retract.
If I shorten the shaft enough to not hit the screw then I will have less than full thread engagement when the drive pin is in the full UP position.

That green block will have a ball bearing in it to help support the motor shaft and there is a stiffener to help stiffen the shaft and give the bearing something to ride on other than threads. That stiffener will be threaded and installed with red loctite.

My initial options are...
1. Use steel instead of bronze for the Drive Pin and only having .09 of thread engagement at the end. I don't like this idea.
2. Make the drive pin with a shoulder on the motor side. Makes the pin not round so a lot more work to make.

It is late and time to go to bed, maybe it will make more sense tomorrow.........

CAD layout section view with the gear Down.



CAD layout section view with the gear UP.

 

[Flyinfool]

Well I did come up with one more possibility, that would be making a whole new rotating block that is about .125 longer to allow moving that pesky clamp bolt farther out to clear the drive screw. That block has a LOT of precise machining on it that will require a bunch of new cutting tools and a lot of tricky setups.

I am not sure this is the route I will go yet. Still pondering........

 

[verbotenwhisky]

Well I did come up with one more possibility, that would be making a whole new rotating block that is about .125 longer to allow moving that pesky clamp bolt farther out to clear the drive screw. That block has a LOT of precise machining on it that will require a bunch of new cutting tools and a lot of tricky setups.

I am not sure this is the route I will go yet. Still pondering........

Do you have any videos of your jet flying?

 

[Flyinfool]

Unfortunately no I don't.
I do not know anyone with a halfway decent video camera that has a clue how to use it.
It is difficult to vid a jet, It is moving fast, this one has a level cruise speed of about 160 MPH. It can also safely pull over 20 Gs in a turn so it is hard for a cam to follow it.

 

[verbotenwhisky]

Unfortunately no I don't.
I do not know anyone with a halfway decent video camera that has a clue how to use it.
It is difficult to vid a jet, It is moving fast, this one has a level cruise speed of about 160 MPH. It can also safely pull over 20 Gs in a turn so it is hard for a cam to follow it.

I understand...

 

[Flyinfool]

I am beginning to lean toward making a whole new rotating block. I would have to do some machining on the existing blocks for needed clearances anyhow. The current blocks are showing wear from years of landings on a rough runway. Those blocks take the full load of 25 lbs of airplane falling out of the sky and then bouncing along a rough grass field. Landing speed is around 30mph The hole that the actual leg of the gear goes into has stretched over time to where I now have a piece of shim stock to make the strut fit.
This will require some new tooling for making some of the cuts and fixturing.

 

[C-Bag]

I am beginning to lean toward making a whole new rotating block. I would have to do some machining on the existing blocks for needed clearances anyhow. The current blocks are showing wear from years of landings on a rough runway. Those blocks take the full load of 25 lbs of airplane falling out of the sky and then bouncing along a rough grass field. Landing speed is around 30mph The hole that the actual leg of the gear goes into has stretched over time to where I now have a piece of shim stock to make the strut fit.
This will require some new tooling for making some of the cuts and fixturing.

I don’t know if this applies specifically but I’ve always had more problems with trying to repair something then making new. So few times do I find the perfect replacement and then you throw in the wear and the whole thing gets really complicated. You are way ahead of the game it seems in that you are good at CAD. I’m not.

Just out of curiosity why is the track have undulations? To keep the mechanism from only wearing on one point in its travel?

 

[Flyinfool]

The undulation is so that the gear will lock over center at the full up and the full down with little to no force on the drive mechanism.
If you look at the full up and down positions, when you try to move the gear block you can see that the slot in the block is pushing the drive pin almost straight against to wall of the undulation and very little pressure against the drive screw of the motor. This way the motor does not see the landing forces and also does not see G forces in the air that are trying to move the gear in or out. The motor and drive only has to be strong enough to lift and lower the weight of the wheel and leg.