Height adjustment mechanism for slider crank mechanism

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Discussion Overview

The discussion centers on the design of a height adjustment mechanism for a slider crank mechanism, specifically aimed at converting rotational motion into adjustable linear motion. The project requires the linear movement to oscillate within specified ranges, and participants explore various mechanisms that could facilitate this adjustable motion.

Discussion Character

  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant describes the basic operation of a crank and slider mechanism with a slotted link that allows for height adjustment through a pin moving along the link.
  • Another participant suggests that a super-fine-tooth rack and pinion could be a viable solution for achieving the desired adjustable motion.
  • A different participant recalls a method using an eccentric to adjust the height of the 'Big End' center, which would affect the effective piston stroke, and references historical steam engine designs for further inspiration.
  • One participant asserts that the Stephenson valve gear mechanism is appropriate for achieving the adjustable motion required, emphasizing its historical significance and functionality in steam engines.

Areas of Agreement / Disagreement

Participants present multiple competing views on the appropriate mechanism for achieving adjustable linear motion, with no consensus reached on a single solution.

Contextual Notes

Some suggestions depend on specific interpretations of the mechanisms discussed, and the effectiveness of each proposed solution may vary based on the project's requirements and constraints.

Deepanjali
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In the current project, I need to convert rotational motion into linear motion using a crank and slider mechanism. The project requires the linear movement to range from 7 cm to 15 cm. Additionally, the system should allow for manual adjustment of the height, so the linear motion can oscillate from 0 cm to 8 cm, 0 cm to 9 cm, and so on, as needed. Can you suggest the appropriate mechanism to achieve this adjustable motion?

Mentor note: Thread moved to homework forum from technical forum, so no template.
 
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Welcome to PF.

A rotating crank, with a connecting rod, rocks a slotted link back and forth about a fixed fulcrum.
A pin, in the slotted link, moves in proportion to its position along the slotted link.

https://en.wikipedia.org/wiki/Stephenson_valve_gear
 
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IIRC, there was a solution using eccentric to adjust height of 'Big End' centre, hence effective piston stroke.

You may find more inspiration for adjustable stroke among the 'variant' steam engines etc here...
http://www.douglas-self.com/MUSEUM/museum.htm
Note: As few such proved to be commercial successes, 'Due Care' advised...
 
Deepanjali said:
Can you suggest the appropriate mechanism to achieve this adjustable motion?
The appropriate mechanism is the Stephenson valve gear, or a simple derivative of that. It gave steam engines every combination of variable valve timing from full forward to full reverse, all by moving one control lever. First applied in 1841, it is still in use today.

You do not need inspiration to reinvent something, you need only understand the Stevenson valve gear mechanism. It may look complicated when surrounded by an entire steam engine, but in any of its forms, the mechanism is really just a rocking bar that does the job.
 
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Likes   Reactions: Nik_2213

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