Uni-Directional Brake: Best Way to Accomplish

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Discussion Overview

The discussion centers around the design and implementation of a uni-directional braking mechanism for a rotating disc. Participants explore various mechanical solutions that minimize friction in the free spin direction while providing instant hold against reverse rotation when the driving force is stopped.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a mechanical solution for uni-directional braking with minimal friction and backlash.
  • Another suggests a well-lubricated ratchet, noting that design variations depend on friction, backlash tolerance, and reverse torque requirements.
  • A participant emphasizes the need for a mechanical solution, explicitly excluding magnets or solenoids, and reiterates the requirements for low rolling friction and minimal backlash.
  • One suggestion involves using bearings or rubber bearings instead of a ratchet mechanism.
  • A participant mentions one-way clutches as a potential solution, linking to external resources for further exploration.
  • Another participant proposes a sprag clutch, acknowledging that mechanical solutions may not be silent.
  • One contributor recommends a one-way bearing, sharing personal experience with its application in RC helicopters, while also noting potential complexity and cost issues.
  • A participant shares a resource for finding locking devices from old copiers, suggesting it could be a practical approach for sourcing components.
  • Another participant identifies a specific product called a Roller Ratchet, which they found after researching, expressing satisfaction with their purchase.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best mechanical solution for uni-directional braking, with no consensus reached on a single approach. Various mechanisms such as ratchets, bearings, and clutches are discussed without agreement on the optimal design.

Contextual Notes

Participants express varying requirements for friction, backlash, and torque, indicating that the effectiveness of proposed solutions may depend on specific application contexts and constraints.

zydubion1
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Can someone direct me to the best way to accomplish uni-direction braking of a rotating disc. I want very little friction in the free spin direction of rotation, and when the driving force is stopped, I need instant hold from reverse direction spin. Like a ratchet but quiter and smoother.
 
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A well lubricated ratchet? :)

The design of such a device could vary greatly depending on how little rolling friction you desire, the amount of backlash you can tolerate and how much reverse torque the device needs to withstand.
 
Sorry, I should have specified that this must be mechanical, no magnets, electromagnets, solinoids etc. Want VERY little rolling friction, and zero to mimimum backlash. Reverse torque is in the range of 10 ft/lb.
 
Instead of a set of teeth...why not apply a bearing?...or rubber bearings.
 
Something like a sprag clutch but it probably won't be silent. Nothing mechanical will be silent.
 
What you want is a one-way bearing. I am very familiar with them as I use them in my RC helicopter for autorotation. They have very little friction and provide very smooth rotation in one direction but prevent any rotation in the other. They work very well when used properly but because of their complexity they can be very expensive (for nice ones) and can also be very prone to failure.

OneWayBearingSpragueDetail_700.jpg
 
Thanks to all for you input. Good stuff!
 
Topher,
That bearing is actually a small version of a sprag clutch by the looks of it. I have never seen those. Who makes them?
 
  • #10
zydubion1 said:
Sorry, I should have specified that this must be mechanical, no magnets, electromagnets, solinoids etc. Want VERY little rolling friction, and zero to mimimum backlash. Reverse torque is in the range of 10 ft/lb.

This is a good place to start.


http://www.smallparts.com/features/fathersdaygifts/?utm_source=internal&utm_medium=homepage_banner&utm_campaign=gifts_for_dads_6_2_09

If cash is a problem, go to some copier repair places, sometimes they will give the old ones away, the old behemoth copiers (and I guess the newer ones that do everything) are filled with different types of locking devices. A little work involved, but lots of interesting things can be pulled out.

Ron
 
  • #11
FredGarvin said:
Topher,
That bearing is actually a small version of a sprag clutch by the looks of it. I have never seen those. Who makes them?

It basically is just a sprague except instead of having a ratchet like mechanism it just uses friction. The bearing is from an Avant Aurora RC heli, I'm not sure who makes it though. SKF maybe?
 
  • #12
After searching based on information on various posts to this forum, I have been able to locate exactly what I was looking for. It's called a Roller Ratchet. Available from www.omegatec.com I purchased one and it is fantastic. Thanks everyone, you are the best.
 

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