- #1

DaveC426913

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- Summary:
- Is it geometrically possible to have an extensible scissor arm that tapers from large to small?

This is what I am calling an extensible scissor arm:

This one is symmetrical - the same breadth along this entire length. I'd like to design one that

I realize that will change the geometry of each section - they will get shorter and shorter - but

When I imagined it in my head, it was fairly straightforward - a simple incremental scaling-down of the parts, as well as moving each central pivot asymmetrically:

But the moment I started sketching it out, it became quite a bit more complicated. The lengths of each spar are not a simple relationship - the scaling factor is

I have a gut feeling that the problem I will run in to is that the extension amount will be "conserved" from left to right - i.e. a small extension at the right will propagate to form a large extension on the left (like a wave breaking on a sloping beach). The left end will reach its extension limit long before the right end will, meaning its extensibility will be wasted (overengineered).

I'd still be interested in feedback, in case there's a way out of this trap I have not divined yet.

This one is symmetrical - the same breadth along this entire length. I'd like to design one that

*narrows*from one end to the other.I realize that will change the geometry of each section - they will get shorter and shorter - but

**is it doable**?When I imagined it in my head, it was fairly straightforward - a simple incremental scaling-down of the parts, as well as moving each central pivot asymmetrically:

**
**But the moment I started sketching it out, it became quite a bit more complicated. The lengths of each spar are not a simple relationship - the scaling factor is

**shared**between left and right (orange and brown) spars in a way that is not immediately apparent. I'll have to experiment, but I'm sort of going by trial and error.I have a gut feeling that the problem I will run in to is that the extension amount will be "conserved" from left to right - i.e. a small extension at the right will propagate to form a large extension on the left (like a wave breaking on a sloping beach). The left end will reach its extension limit long before the right end will, meaning its extensibility will be wasted (overengineered).

*EDIT: Yeah. The more I think about it, the more I see that the maximum extensibility is determined by the smallest arm. Any arms larger than the smallest are wasted. Which is why there's no such thing as a tapered scissor arm.*I'd still be interested in feedback, in case there's a way out of this trap I have not divined yet.

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