Constant torque spring - damping question

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Discussion Overview

The discussion revolves around the design challenges associated with a constant torque spring used in a Geneva mechanism, specifically focusing on achieving a slow rotation of the drive wheel while also requiring high torque for a brief period. Participants explore potential solutions, including the use of rotary dampers and flywheels, to manage the rotational speed and torque requirements effectively.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests using a rotary damper to slow down the drive wheel's rotation when not engaged with the Geneva wheel, but questions how to disengage the damping when high torque is needed.
  • Another participant proposes the idea of incorporating a flywheel to help manage the irregularities in angular momentum required during operation.
  • A different viewpoint indicates that a liquid rotary damper may not prevent full torque delivery but could limit the rate at which torque is delivered.
  • One participant critiques the idea of damping for most of the rotation, arguing it may waste energy, and suggests using a heavier drive wheel instead to manage speed changes more effectively.
  • Another participant mentions that using a constant force spring does not inherently waste energy when slowing rotation during part of the cycle.
  • The original poster expresses a need for a rotary damper that can handle a specific torque and maintain a low rotational speed, while also noting size constraints for the component.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best approach to manage the torque and speed requirements, with no consensus reached on a single solution or design. The discussion remains unresolved regarding the optimal method to achieve the desired functionality.

Contextual Notes

Participants have noted constraints such as size limitations for components and specific torque requirements, which may affect the feasibility of proposed solutions. There are also unresolved questions about the effectiveness of different damping methods in achieving the desired performance.

DaanW
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Hi all,

I have a constant torque spring that rotates the drive wheel of a Geneva mechanism. I am facing the following problem. I would like a very slow rotation of the drive wheel whenever the drive wheel is not driving the Geneva wheel of the Geneva mechanism (which is 270 degrees of a rotation). However, when the pin of the drive wheel rotates the Geneva wheel by 90 degrees, I need a lot of torque because there is a load connected to the Geneva wheel. Therefore, I need to use a high torque constant torque spring (7.50 in-lbs.).

I think that a rotational damper can help me slow down the rotation of the drive wheel (it is a timing mechanism, and the rotational velocity should be ~1 rpm), but when getting to the point of rotating the Geneva wheel, I would need the damping to be gone (because there, I need full torque).

Does anyone have a suggestion for a rotary damper that is capable of doing this? Or are there other ideas/designs that can solve the same problem in your opinion?

Thanks in advance!
 
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Hallo Daan, :welcome: !

How about a kind of flywheel to even out the irregularity of the angular momentum required ?
 
Do you need a change in rotation speed; if not, a liquid rotary damper will not prevent the mechanism from delivering its full torque, it will only limit the rate at which the torque can be delivered.
 
It's not logical to dampen the drive wheel for 3/4 of the time: waste of energy.
Still in favour of the flywheel idea :rolleyes: - but even that has air resistance; perhaps it's better to use a heavy drive wheel that slows down during 1/4 turn of work and revs up 3/4 turn ?
 
If you are using a constant force spring for the full rotation then there is no waste of energy if you slow the rotation for the 3/4 portion.
 
Thanks for the replys. An additional constraint is that the component can't be any bigger than 1 inch diameter.. I think I can solve the problem by using a rotary damper, only problem now is to find one that can resist a ~1 N*m torque and bring the rotational speed down to ~1-2 rpm. Let me know if you have a design/manufacturer for such a component. Many thanks!
 

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