Counterbalancing the trapdoor. Pt.3.

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Friday: I measured the load required to lift the trapdoor at half way along its length. Minimum of 13kg but actual lifting is not required. Just enough force to make the job of opening and closing the trapdoor fairly effortless. Cables or ropes would run inside the stepladder's handrails to avoid obstructions when climbing the ladder. I certainly don't want t trip wires near floor level! Grooved pulleys can be fitted to the the insides of the handrail extensions.

After passing over the pulleys the cables or ropes would drop through small holes in the floor beyond the top tread of the ladder.  Weights will hang just above the ground/floor of the obs. building to reduce the risk of damage from falling. Downside is that the trapdoor can't travel beyond the pulleys.

See image right for a quick mock-up. The crossbar would be replaced by individual 4" pulleys fixed near the tops of the handrail extensions. I have arranged the ropes to put the weights up high with the trapdoor down. These temporary weights just reached the floor when the trapdoor was fully raised. They aren't heavy enough to lighten the trapdoor properly and the real ones would rise and fall out of sight down near the floor in the lower building. This area is under the stepladder so no foot traffic is possible.

A simple hole in the obs. floor will suffice to let each rope pass unhindered. There is no need for a slot where a rope runs over a pulley to fall vertically under the tension of a weight.

Weights and levers might still be preferable but difficult to arrange. This is due to the angle which has to be covered from trapdoor flat [closed] to beyond upright. Approximately 0-107 degrees at present. I am using sliding door bolts to secure the heavy trapdoor from falling back down again.Though in practice the trapdoor is leaning well past the vertical when open. Once counterbalanced there should be no risk of the trapdoor falling accidentally.

Click on any image for an enlargement.

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