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[ballastanksian]

That array of detail looks very well Paul. The screw and captured nut idea sould work well as long as the screw threads are absolutely parallel. Perhaps worked through a few times with some valve grinding paste just to loosen the threads up a bit before fitting everything together will reduce friction and possible distortion.

[Rob47]

On Hermes  I used scissors action driven by one long threaded rod, positioning controlled by micro switches, worked a treat, very quiet and quite scale looking

[Paul Swainson]

Hi Rob,


Do you have photos and or drawings of the system you used.  If so would like to see how it was done.

[Paul Swainson]

Had a wee think and came up with this idea using the system of four shaped guide post one on each corner running down to a support platform below the level of the hanger deck. This would give the lift support on all corners.  Grooved would suit and easy to shape from B&Q picture frame wood.  The base of the lift would have a cross section made from copper or light alloy with a centre point holding a screw rod about 65 mm long.  The distance of travel will allow the rod to fil in below the hanger deck and can be controlled using  a nut with a groove cut to control the rod travel.  ( I think) have to see if that will work.  Simple drive motor with two limit switches. 


Thats my first idea.

[Rob47]

Hi Rob,

Do you have photos and or drawings of the system you used.  If so would like to see how it was done.

Sadly no and she is long gone but will see if I can draw something for you, might be a bit rough though

[Rob47]

Paul
Hope this makes sense, if not PM and I will give you my phone number and I can talk you through it.  It basically was two H frames with a swivelling cross piece between each one, one had a support hole in it the other had a nut fixed to it  Both frames ran in rails and when the motor powered up the shaft turned and either pushed the H frame away or drew it in.

[Paul Swainson]

Hi Rob,


Thanks for that and got the idea,  will see how thinks go and will show how I get on.  Once again thanks for the information.

[derekwarner]

Paul............the Scissor Lift design suggested by Rob47 is essentially a design used in thousands of RO-RO vessels for movement of product [coils or slabs] between decks

With care & attention to scale robustness it would make an absolutely reliable/workable solution  to your requirements

Derek

[warspite]

Just type images of scissor lift into any search engine and there will be countless number of images of these to help the design.

[Geoff]

Correct me if I'm wrong but for a scissor lift don't you have to have a left and right hand thread to make it move truly vertical? Otherwise it will pivot about one axis. Its quite possible to purchase left hand taps and dies but they are not cheap but I agree the motion would be very good.

Cheers

Geoff

[Rob47]

Geoff
You may be correct but in my configuration on Hermes (as sketched) it worked and no issues, it is only winding one of the H arms in or pushing it out so I don't see the need for left and right thread. Suffice to say it worked and all designed on a table in my room in the mess 

[Paul Swainson]

Think this will do the job with just one layer of scissor with one gear on each screw rod driven by one centre gear cog connected to a motor.  Would have to work our where to put the limiters on for top and bottom.
https://www.youtube.com/watch?v=VEJzHizTYSU


Would make a compact set up.



Also found this picture but with a single screw.  Not sure if it would be stable, may dip or be springy on either side if load not central.

[Geoff]

As an alternative you could consider a screwed rod on one side with a 90 degree support under the lift so turning the rod elevates the lift up and down with the sides running in guides. A micro switch top and bottom act as limiters. This would give a very direct vertical movement with no chance for misalignment.

Good luck

Geoff

[Paul Swainson]

I have completed the lift cage which will mount on the support floor and have made the support beams and temp fitted the setup for height and position in the hull.  The lift floor slides up and down without binding. 


Question is there a method on how to work out the lengths of the scissor arms so that I can keep them within the the size of the cage!  Understand the fixed rear scissor arm will be the same length as the lift floor.  Is the other one shorter?

[Rob47]

mine were both the same length, also I may be wrong but in the image it looks as if the arm moves along the lift, mine were fixed to the underside, also as Geoff said I had micro switches as stops, no other support and it dropped into the well rather well, centralising on the lift should not be an issues as the plane will have to be central.  Good luck Paul, your almost making want to build Hermes again, but Bristol to finish then HMS Gloucester 1/72

[Paul Swainson]

So when making the scissor arms each side is on a central pivot, the top arms are fixed to the under side of the lift frame.  The lower arms of the scissor one side is fixed to the base and the other side is able to slide along guides each side.  The drive screw when operated by the motor it will pull the scissor action together to raise and push to lower.


Do I really need two screws or one.  If I used two screws can the be of the same right hand thread.

[Rob47]

Paul
as I said I used only one, do not see a need for two, it simply a bolt (long one) being screwed into then out of a nut, the idea was encompass the KISS principle and it seemed to work.


Bob

[derekwarner]

Paul......this is what I meant ......'with care & attention to scale robustness'

One main drive screw will work......two main drive screws has the potential for the lift floor to bind/skew/seize 

Derek

[Paul Swainson]

Well make up of the scissor lift failed.  The arms of the scissor was too long. I made them the same length as the left base but when connected up there was to much hight and offset the top platform to the front.  If the next attempt does not work will go for the single screw as per my first plan.

[John W E]

Hi there Paul

Have you thought of using the principle that the new old Ark Royal used to use?   Form of a Y Fork Lift - the principle is quite simple, you could replace the hydraulic rams with threaded screw bar or you could use cable and a sale winch servo.

john

[derekwarner]

Oh no shock horror there Bluebird  .......[beautiful picture......all reminiscent of HMAS Melbourne]

Just imagine trying to replicate that hydraulic nightmare in mechanical linkages 

We see opposing principal cylinders for the major lift, opposing secondary cylinders, 3 of 4 lowering cushion cylinders.....a bank of Fawcett Cristie hydraulic accumulators, a Filter Pall filterstand......a pump station, 3/4 of a ton of headache load sensing servo controlled valving all designed in theory to keep the platform level  ...... if a Loading Officer managed & misplaced the footing of a 3 ton Turbo Prop  Fighter

I think Paul is far better keeping the Y front for his jocks & maintaining an X frame with single screw platform lift

Derek

[Paul Swainson]

The second attempt was worked out on paper with detail measurements and the size of the left base would not allow a scale version of a scissor lift to work the arms would not work within the cage and the depth was not good either.  So now making my first idea and will post photos of the build and working in the lift case, before installation.  Just need to work our how to set up the drive motor and the limit switches.   

[derekwarner]

Morning Paul.......there are a number of considerations for limit switches in model structures.....

1. install the switching in the drive unit......+ accurate repeatable positioning, .... - difficult to attain in scale versions with the switching being relative to the pitch of the threaded hoist rod 

2. install the switching externally with the load as the switching interface.....+ easier to accurately limit of movement, ..... - can be difficult to disguise the equipment

The great image from bluebird shows 3 of 4 lowering hydraulic cushion cylinders from Ark Royal ......the hoist frame plate comes to rest on these 4 cylinders when fully retracted....they are also load sensing so each one sends a hydraulic signal to stop the main cylinders retracting any further

It would be pretty simple to install 2 micro switches [on the diagonals under the floor of the hoist frame plate] with small tubular extensions, their function replicates that of the original

Hoisting limits could be mounted in a similar manner under the main upper deck of the carrier

I am pretty sure hoisting & lowering could be achieved by using DPDT [double pole/double throw] limit switches, however I would stand back and ask a member knowledgeable in the Black Arts for confirmation

The image below from Ark Royal with one of the lowering hydraulic cushion cylinders shown [fully extended]....the rod spherical round landing pad is also seen in the rod closer to the camera

Derek

[John W E]

Hi Derek

partially correct - the 4 hydraulic rams at each corner are there to give initial lift to help the main hydraulic rams when they first start the lift from the ground position - the sensors for up and down are actually on the edge of the lift platform.  Here is a better picture.
john

[Paul Swainson]

The forward lift cage has been made and positioned in the hull with the lower deck supports in place to obtain the lift height.