[LT] Portcullises

[vicky_molokh]

Originally Posted by Figleaf23

Drawing raw ropes over a rough beam would be more efficient than this mechanism!

Strictly speaking, how much they can lift is a function of their weight, not their strength.

[Figleaf23]

Originally Posted by vicky_molokh

Strictly speaking, how much they can lift is a function of their weight, not their strength.

The depends on the mechanism, but, yes, it's true of a pure conversion of the force to a downward pull. But that points up even more the questionablity of needing 8 men to draw up 450 lbs.

[vicky_molokh]

Originally Posted by Figleaf23

The depends on the mechanism, but, yes, it's true of a pure conversion of the force to a downward pull. But that points up even more the questionablity of needing 8 men to draw up 450 lbs.

I was referring to raw rope(s) over a beam that you mentioned.

[Edges]

450 lbs sounds a bit light.

[Anthony]

I feel like that sentence about the lifting mechanism is referencing text that no longer exists. In any case, a mechanism that allows lifting a 450 lb object at 1'/3s is doing about 200W of work, and with good axles could be done by one person.

[Ze'Manel Cunha]

Originally Posted by Anthony

I feel like that sentence about the lifting mechanism is referencing text that no longer exists. In any case, a mechanism that allows lifting a 450 lb object at 1'/3s is doing about 200W of work, and with good axles could be done by one person.

Sounds like someone dropped a factor somewhere...

15 lbs for a 10 foot square grate of iron also seems a factor too light.

If we were looking at a small portcullis bars which were say 2" on a side, we could calculate the weight of each 15' bar at:

15' = 180" = 450 cm
2" = 5 cm

5x5x450 = 11250cc x (Iron at 7.80 g/cc) = 87,750 grams

So each 15' bar would weigh 87.75 kg, or 193 lbs.

Each 10' bar at:

20' = 240" = 610 cm
2" = 5 cm

5x5x610 = 15250cc x (Iron at 7.80 g/cc) = 119,000 grams

So each 20' bar would weigh 119 kg, or 262 lbs.

If all the bars are 1' apart, and the gate is 20' wide, we'd have 21 bars which are 15' high, and leaving sharp ends we'd have 15 bars which are 20' long, that'd add up to:

(21x193) + (15x262) = 7,980 lbs ~ 4 tons


Having 8 men raise a portcullis which weighs 4 tons isn't unreasonable...

(Someone please check my math if you will.)

[Figleaf23]

Originally Posted by Ze'Manel Cunha

Sounds like someone dropped a factor somewhere...

15 lbs for a 10 foot square grate of iron also seems a factor too light.

===================

I was confused by that at first too. However, upon rereading it refers to 10 square feet (3.16' x3.16'), not 10 feet square.

[Figleaf23]

Originally Posted by vicky_molokh

I was referring to raw rope(s) over a beam that you mentioned.

Yes, I know. The fact that a system that permits the crew to use weight rather than ST (3 average men weigh 450, a fourth would overcome the fricton of the rope) would be so simple makes it even stranger that anyone would build a mechanism that needs double the men.

[Lord Carnifex]

I don't know about 8 men, but I would imagine a well constructed mechanism is going to have a ratchet system installed, so that if someone slips, the whole thing doesn't slide down. That will add some mechanical resistance, although not four people's worth.

[Figleaf23]

Originally Posted by Lord Carnifex

I don't know about 8 men, but I would imagine a well constructed mechanism is going to have a ratchet system installed, so that if someone slips, the whole thing doesn't slide down. That will add some mechanical resistance, although not four people's worth.

Any kind of decent counter-weight system would mean that the only work the crew needs to contribute is control and overcoming the resistance of the mechanism itself.