Mechanism to Reverse Rotating Axle with Friction: Ideas Needed

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Discussion Overview

The discussion revolves around designing a mechanical mechanism that can reverse the direction of a rotating axle when excessive friction is encountered. Participants explore various mechanical solutions, including the use of springs, gears, and clutches, while addressing the challenges associated with maintaining functionality over multiple cycles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Chris seeks a mechanism that reverses the direction of a rotating axle when friction becomes too high, preferring a solution using purely mechanical components.
  • Some participants inquire about the specifics of the frictional torque and the driving force behind the axle, questioning whether reversing the axle will eliminate the frictional torque.
  • Tom proposes a concept involving concentric shafts, a torque-limiting clutch, and a planetary gear system, suggesting that the clutch could drive a pawl to shift or lock the gear train.
  • Chris expresses confusion about the pawl mechanism and raises concerns about the need for the pawl to unlock for repeated operation.
  • Another participant suggests researching "Tumbler gears," which can toggle between forward and reverse motion, proposing a spring-loaded mechanism that could switch direction under overload conditions.

Areas of Agreement / Disagreement

Participants have not reached a consensus on a specific mechanism. There are multiple competing ideas and uncertainties regarding the functionality and practicality of the proposed solutions.

Contextual Notes

Some participants note the need for further clarification on the mechanics of the proposed solutions, particularly regarding the behavior of the pawl and the implications of friction remaining after reversal.

Who May Find This Useful

Individuals interested in mechanical design, particularly those exploring mechanisms for reversing motion in response to friction, may find this discussion relevant.

Chris184
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Hello,

for my current physics-project i am searching a mechanism:
When there is to much friction on a rotating axle, it should reverse the direction and go on, till the mechanism starts all over again. I would love to solve this with pure mechanical parts, like springs gears etc...

If you have any ideas on how to realize this mechanism, or even an existing mechanism, please share your thoughts with me. I am happy about every idea.

Thanks, Chris

p.s.: and sorry for my english, I am from Austria ;)
 
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Welcome to the PF.
Chris184 said:
When there is to much friction on a rotating axle, it should reverse the direction and go on, till the mechanism starts all over again. I would love to solve this with pure mechanical parts, like springs gears etc...
Can you describe the behavior a bit more? What is applying frictional torque to the axle? What is driving the axle against that frictional torque? Will reversing the direction of axle rotation zero out the frictional torque, or will it remain just as strong after the reversal?
 
I don't know how practical, but this concept comes to mind.
  • concentric shafts, one the drive the other driven
  • a torque-limiting clutch, as used in some battery operated screwdrivers
  • planetary gear system coupling the two shafts
  • when the torque-limiting clutch slips it drives a pawl that shifts (or locks?) the planetary gear train
Still lots of details to work out!

Cheers,
Tom
 
"...drives a pawl that shifts (or locks?) the planetary gear train"

thus reversing the rotation of the driven shaft. (Is this what you mean to say?)
 
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berkeman said:
Welcome to the PF.

Can you describe the behavior a bit more? What is applying frictional torque to the axle? What is driving the axle against that frictional torque? Will reversing the direction of axle rotation zero out the frictional torque, or will it remain just as strong after the reversal?

Yes sure. There is a torqueslip built into a linear actuator. The linearactuator shall be driven in and out by this mechanism. When reversing the direction the friction will remain as strong as before the reversal.
Thanks for your comment.
Tom.G said:
I don't know how practical, but this concept comes to mind.
  • concentric shafts, one the drive the other driven
  • a torque-limiting clutch, as used in some battery operated screwdrivers
  • planetary gear system coupling the two shafts
  • when the torque-limiting clutch slips it drives a pawl that shifts (or locks?) the planetary gear train
Still lots of details to work out!

Cheers,
Tom

Hey Tom, thanks for your idea. It was helpful. Even tho i did not completely understand the pawl. The problem which comes in my mind is that the pawl has to be unlocked again, since i want the mechanism to be repeatet more than twice. Do you understand my concerns, or did i misunderstand you?

Thanks for your comment!
 
Last edited:
AZFIREBALL said:
"...drives a pawl that shifts (or locks?) the planetary gear train"

thus reversing the rotation of the driven shaft. (Is this what you mean to say?
Yes.

Chris184 said:
Do you understand my concerns, or did i misunderstand you?
Probably a bit of both!

Chris184 said:
When reversing the direction the friction will remain as strong as after before?[/color] the reversal.
I think that shoots down my (shadow of an) approach. But I do wonder how the driven element doesn't immediately switch back to the first direction.
 
Google 'Tumbler gears'.
Two gears that act forward or one of which reverses. Used on the lead screw on a lathe when thread cutting.
Take a look at a thread cutting lathe to see how Left/Right thread is selected.
You could over-centre spring load the gear mount plate so that when it is overloaded it toggles or flips to the other mode and reflects direction.
 
Baluncore said:
Google 'Tumbler gears'.
Two gears that act forward or one of which reverses. Used on the lead screw on a lathe when thread cutting.
Take a look at a thread cutting lathe to see how Left/Right thread is selected.
You could over-centre spring load the gear mount plate so that when it is overloaded it toggles or flips to the other mode and reflects direction.

Thank you very much, that's exactly what i needed!
 

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