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griff2379

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Posts: 19
Reply with quote  #1 
HI
I have a problem with the lifting mechanism.
It will rise very well but locks and does'nt lower.
If the fit between the forks and the vertical bars is good then it will tilt and lock
(the basis of some modern clamps).
If the fit is too loose then it will tilt and shed the load, and still not lower !
A good model to build and paint, I used brass tube for the vertical bars to withstand over-enthusiasm ! P1010180.jpg

Wombat

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Reply with quote  #2 
This sort of problem is commonly overcome by using a closed loop string; ie when wound downwards, the string on the bottom pulls the load down, rather than relying on gravity.
 With the suspended winder mechanism separated from the body, it gets a bit hard, but you could do two strings side by side. The crank shaft has one string wound clockwise on one end and the other string wound anticlockwise on the other end.
One of the strings must freely go through a hole in the lift tray, loop around a "pulley" in the base , and back up to join the other string fixed to the lift tray.

You will need to adjust the relative amount of string wound each way so that as one side unwinds, the other winds up.
 ( hard to describe in words)
Then, wind handle one way, pulls up, wind other way pulls down.
 Have not yet built this model myself yet, but had this mod in mind to overcome a perceived problem that you have confirmed. [smile]
 Give it a try and let me know if it works![wink]
 Love your brass tube modification, way tougher ( and more realistic) than dowel.
Thanks for the inspiration.

griff2379

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Posts: 19
Reply with quote  #3 
Hi Wombat
OK then I need a pivot point in the body work and in between the two upright bars ( possibly a simple eye screw)
I'll give it a try and post the result
Thanks for your input
Griff
Peter V

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Reply with quote  #4 
Griff,

is it a possibility that you put some extra weight into the fork? For example, a piece of lead (fishing shop??) in a made groove? Maybe enough for the gravity to fall in???

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Peter V
griff2379

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Posts: 19
Reply with quote  #5 
Hi thanks for your interest.
I would never put small pieces of lead in a toy.
The problem is the mass of the forks(shelf)(tray) so the answer may be the way Wombat suggested or by using two pieces of tube (one inside the other) Screenshot 2019-12-01 at 18.24.37.png  Screenshot 2019-12-01 at 18.26.17.png

Wombat

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Reply with quote  #6 
Griff,
 I like the idea of two sliding tubes.
Effectively that increases the length of the reaction force base, leading to less jams, BUT.....
even 1/4" extra protrusion  above and below the fork tray limits its travel accordingly. You should probably stick them all the way out the top, limiting the height lifted but allowing full lowering. Perhaps make the brass columns just that bit longer to compensate?

Wombat

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Reply with quote  #7 
Hi griff
  had a bit more time to think this out, consulting my copy of the plan.
 I have marked up how I plan to do mine ( going to be fun winding a few loops around the winder axle in-situ, but hey, as the girl said to the sailor " if it isn't hard, it isn't fun!" )
 You might even be able to try it out on one of your two, without building a whole new one.

EPSON001.jpg 
As one side winds up, the other unwinds, so never more than three loops on the axle so it won't jam ( I hope)

griff2379

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Posts: 19
Reply with quote  #8 
Ok Wombat.
To try all these methods I will have to make a few more ! ?
Thanks for the ideas. I'll let you know but don't hold your breath !
Griff
Peter V

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Reply with quote  #9 

Griff,

I mean with lead ... lead (or iron) but completely build in and hidden out of sight in the wood so nobody will know it is there.

The position at which I would try to fix that, is in the piece of wood between the two stands via which the forks are moving up/down.

I made some in a plan which had the urge to fall onto it's nose because of the weightbalance/tail. 


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Peter V
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