Ratcheting Mechanism Choice Help

I have a somewhat odd question. I need help looking for a ratcheting mechanism that would fit a certain criteria.
-Be able to hold back at least 300 lbs
-Be able to be instantly released under full load of 300+ lbs

I am thinking something like a boat winch except it should be able to be released instantly. Thanks for any help.

-F0ur13r013

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A suggestion. Two separate mechanisms. Shifting and ratcheting. By shifting to a “neutral” that allows free spin, you can release the load. Should enable you to use just about any COTS shifting gearbox.

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Okay, that is a good idea. Do you have any suggestions/links that could lead me in the right direction towards finding a suitable shifting mechanism? Thank you.

Your 2020 infinite recharge robot uses a shifting gearbox for a similar use case. One stage is ratcheting and the other one is neutral on the climber gearbox. I can walk you through it next time I’m in the shop

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Okay. I thought we used something like I just didn’t know how much weight it could hold.

What’s the application? Something @hutchMN or I could help with since we’re both mentors for your team?

No - don’t help him. I want to see how this develops sans 4607. I have no idea what is going on or where this could go. But I am intrigued.

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Lucas and Adam and I where dreaming up ideas for the Twins game robot awhile back using a powerful spring to launch a ball. FAST. Hopefully.

But with control? Yes?

Hopefully :crossed_fingers:

CD has truly come full circle.

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You could do some kind of choo-choo linkage with a ratchet. It only requires the motor to spin one direction, but allows rapid release of something like a spring. Choo Choo Mechanism - YouTube

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Interesting, I will have to look into that.

You can look into 2014 robots for various mechanisms to hold back a heavy spring on a catapult. Some solutions I saw then:

  • Shifting gearboxes (with built in clutch), having one set of gears removed (for a neutral) and replaced with a hex ratchet.
  • Choo-choo linkages (but be careful, these have to be built a lot stronger than you think to work)
  • “Snail (or spiral) cams” which pulls back the spring until it falls over a notch in the cam
  • Car trunk latches with air cylinders pulling the cable

Andymark also sells a whole whinch/gearbox/clutch thing that might drop into your design:

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Thanks for the help. I will definitely look into those mechanisms especially the andymark one.

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You’ll find a number of 2010 designs as well for similar use cases.

Specifically for ratchets, in 2010, 294 did a witch-driven pull back with a custom ratchet/pawl connected to a 4 bar linkage for the kicker. There was a huge amount of force on this–probably several hundred pounds worth–generated by surgical tubing attached to the front of the frame, and of course mechanical advantage through the 4 bar radius. It was pulled back by a wire rope winch that would unwinch prior to releasing the ratchet for a completely free motion. It could easily kick a soccer ball the length of the FRC field.

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That is a cool design. And a very interesting take on it.

Just for fun… here’s a picture of it in the real practice robot.

And here is the competition robot on the Einstein field after winning champs :slight_smile:

That’s awesome. I like the flat top exposed electronics design aspect of it.

In general, you might want to research patents for rail cars, trucks, and ships. Many, many brains have pursued locking-but-releasable mechanisms for generations. (One of my great great uncles filed a few rail patents, one of which involves easy release of literally a carload of coal or ore, which might possibly be extended to a ratchet/pawl configuration.) Unless you’re planning to sell it, right?

Without knowing what you’re trying to do, I find myself pretty much agreeing @marshall at least in principle - have two separate degrees of freedom, one of which serves as a ratchet while the other is engaged, but set up so that the other can disengage cleanly.

A neat concept floated on another recent topic with ratchet in the title* involved pushing a rack (linear gear) laterally [that is, parallel to the teeth] into a gear as a brake. If the gear and rack were constructed with pawl-shaped teeth and this push had enough give to allow the pawl to work in one direction, this could get you there.

3946 did something along these lines for our STEAMworks climber - we didn’t need the robot to release the ratchet, but we did need to know we could get it down after the match. We used a 1/2" pass-through ratchet wrench on a 1/2" hex bar that was part of our climber. The wrench was held in place by some probably unnecessary velcro strap. Even when the climber was two-blocked (jammed) against the top of the climber, we could slide the wrench out perpendicularly to the load.

* I’ll let you find the specific post, because reading the topic should give you plenty to think about.

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