How can I design a linear to rotational crank mechanism without using gears?

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Discussion Overview

The discussion centers on designing a mechanism that converts linear movement into rotational movement without the use of gears. Participants explore various configurations and components, including a uni-directional drive and crank designs, while addressing specific application requirements such as speed and movement direction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a mechanism that converts linear movement to rotation, specifically avoiding gears.
  • Another participant questions the requirements, asking if the goal is to prevent the rotational part from driving the linear part, and whether the linear movement is one-directional or reciprocating.
  • A participant clarifies that the linear movement will drive the rotational part and that reciprocating motion is necessary for the crank to function.
  • Concerns are raised about the effectiveness of a conventional crank at low speeds, suggesting it may not maintain consistent rotational direction.
  • A suggestion is made to use a uni-directional drive with a crank that has a long stroke to avoid reaching points where it could get stuck.
  • There is mention of an arbitrary input force that may not synchronize with the shaft's angle, indicating potential complications in design.

Areas of Agreement / Disagreement

Participants express differing views on the suitability of conventional crank mechanisms and the specific requirements for the design. The discussion remains unresolved with multiple competing ideas presented.

Contextual Notes

Participants have not fully defined the parameters of the mechanism, such as the exact nature of the linear movement and the implications of speed on functionality. There are also unresolved questions regarding the synchronization of input forces with the rotational mechanism.

D9 XTC
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I'm looking for a crank that can give me linear movement to rotation (not the other way around).

There is a component that I'm aware of called a uni-directional drive that turns rotation movement in either direction into movement in only on direction... stick a rack in the mix and there is linear movement to rotational. The only thing is is that I don't want to have to deal with gears.

Anyone have any ideas?
 
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D9 XTC said:
I'm looking for a crank that can give me linear movement to rotation (not the other way around).

There is a component that I'm aware of called a uni-directional drive that turns rotation movement in either direction into movement in only on direction... stick a rack in the mix and there is linear movement to rotational. The only thing is is that I don't want to have to deal with gears.

Anyone have any ideas?

Isn't clear what you want that makes a conventional crank unsuitable. Do you want to prevent the rotating part from driving the linear part? Is the linear movement in one direction or reciprocating? Do you need it to be self-starting in any position? A more linear force-torque relationship?
 
My bad

For my application the linear part will drive rotational part. There's no need to prevent the rotational part from driving the linear part but it would be interesting to see if you have ideas for that. The linear movement has to be reciprocating for the crank to work. Not sure what you mean by self starting in any position and linear forve-torque relationship.

The reason why I think a crank with the usual config won't work is because the speeds I'm running are relatively low. Seems like the crank may not be able to rotate the shaft it's connected to the same direction all of the time.
 
Last edited:
D9 XTC said:
The reason why I think a crank with the usual config won't work is because the speeds I'm running are relatively low. Seems like the crank may not be able to rotate the shaft it's connected to the same direction all of the time.

Ah, gotcha. That's what I meant by "self starting", which is a term I just made up :P

How about the uni-directional drive, driven by a crank that has such a long stroke that it never completes a full revolution, so it never hits TDC or BDC where it might get stuck.

I suppose you have some arbitrary input force that can't be synchronized with the shaft's angle the way it is in an engine.
 

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