Ratchet mechanism without springs or gravity? Possible? - Page 1
Forum section: electronics / general

author: Infraviolet
author_rank: Super Contributor
timestamp: February 11, 2023, 07:17:21 pm
content: Consider a ratchet mechanism, a toothed wheel or bar which runs past a levered catch. Usually either a spring, or weight via gravity presses this catch against the teeth, the wheel can turn in only one direction (rt the bar moves linearly in only one direction).Is there any way to make such a mechanism which relies neither on springs (a spring here meaning any piece of material whatever its shape which undergoes some of amount of deformation via compression or bending and resists this with a force which returns it to the normal configuration when possible) nor on gravity (because plenty of applications can be on systems such as joints on robotic arms which might well be in any orientation with rexpect to the gravitational field direction).Thanks

author: Gyro
author_rank: Super Contributor
timestamp: February 11, 2023, 07:41:02 pm
content: Maybe substitute a little friction? Mount a peg on a friction arm and they have it running in a constrained groove in the 'ratchet' wheel (so that the peg is positively guided in both directions sideways). When the wheel is running forwards the peg will be guided side to side by the ramps in the groove, in the reverse direction, the peg will catch on the flats (or recesses if you want stronger locking). A similar track guided arrangement is used in push on - push off switches but substituting a little spring pressure for friction.What's the problem with springs?

author: jpanhalt
author_rank: Super Contributor
timestamp: February 11, 2023, 07:57:52 pm
content: Just have whatever is moving press against a lever/latch to lower it into a cog. Envision a clock escapement without a pendulum. It will only "beat" one click per movement of the latch. Of course, gravity and a pendulum are needed if the clock is to keep time. Nothing new.

author: Benta
author_rank: Super Contributor
timestamp: February 11, 2023, 08:20:06 pm
content: Take an old,fashioned bicycle rear wheel hub apart (you know, the ones where you brake by reversing the pedals). Then you'll see how it's done (hint: think roller bearings).You'll probably find one free at the local garbage dump.

author: Infraviolet
author_rank: Super Contributor
timestamp: February 11, 2023, 08:31:13 pm
content: Gyro, can you link to a diagram or photo? ThanksWhy not springs: I'm interested in working without "spring" like elements, particularly as I'm thinking of trying some 3d printed mechanisms of this form, and want them to be long lasting, and know that living hinge type "springs" in 3d printed parts aren't very durable.Benta, bearings, yes I think I see what you're on about. Thank you.

author: Gyro
author_rank: Super Contributor
timestamp: February 11, 2023, 08:35:44 pm
content: QuoteNot without sitting down and trying to draw it, no. Just think sawtooth shaped groove (actually double sawtooth with alternate slopes in each direction) in the flat surface of the wheel rather than sawtooth shaped edge.Maintaining predictable friction is probably more troublesome than forming a spring with very low flex stress though.P.S. A Verge escapement locks in reverse...https://en.wikipedia.org/wiki/Verge_escapement

author: jpanhalt
author_rank: Super Contributor
timestamp: February 11, 2023, 08:50:00 pm
content: It appears that Infraviolet's question has been answered in the affirmative. Now, what does he/she want to do? Is this just another "what if's?"@Infraviolet: What do you want to do and why?

author: Ian.M
author_rank: Super Contributor
timestamp: February 11, 2023, 08:54:02 pm
content: https://en.wikipedia.org/wiki/Sprag_clutch

author: pqass
author_rank: Super Contributor
timestamp: February 11, 2023, 10:26:40 pm
content: Quote from: Infraviolet on February 11, 2023, 07:17:21 pmPermanent magnets seem like an obvious solution here.

author: langwadt
author_rank: Super Contributor
timestamp: February 11, 2023, 10:39:06 pm
content: one way bearing

author: Psi
author_rank: Super Contributor
timestamp: February 12, 2023, 12:45:56 am
content: Quote from: langwadt on February 11, 2023, 10:39:06 pmyeah, was just going to say that

author: Infraviolet
author_rank: Super Contributor
timestamp: February 12, 2023, 11:30:49 pm
content: Thank you for your ideas, they've given me a good list to look further in to.This has been a sort-of what-if, I don't have an exact application yet, but have some thoughts in my head and wanted to check on the feasibility of a few key features within them before getting more concrete in my ideas. I know I tend to have a habit of asking these sort of questions, considring methods and building up a "library" of solutions before really approaching a problem.

author: jonovid
author_rank: Super Contributor
timestamp: February 17, 2023, 04:45:30 pm
content: coaster brake bicycle hubs have this. the steel rollers jam in one direction only.Quote from: Psi on February 12, 2023, 12:45:56 amnow I know what to call it , its reliable and without the click click click sounds of most ratchet mechanisms , took a bit of time to figure it out.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 22, 2023, 10:23:19 am
content: Something like a centrifugal clutch may work, it will have some "friction" in "pass" directon, and in the "block" direction some pawls could catch behind hooks, or depending on angles, they can also lock on a smooth surface. Some sticky grease can help with extending the pawls in the "block" direction, so there is no dependence on centrifugal force at all.

author: DavidKo
author_rank: Frequent Contributor
timestamp: March 01, 2023, 12:20:56 pm
content: It depends on the application. You can simply use worm drive if the speed reduction is OK for you.

author: Infraviolet
author_rank: Super Contributor
timestamp: March 01, 2023, 06:26:46 pm
content: A worm drive prevents backdriving, turning the output and thereby turning the input, it doesn't do anything regarding allowing one direction of backdriving but not the other though.The magnets idea is the one I'm going to go with when I get to that point in my project, I should have thought of it, so simple but so ideal.

author: DavidKo
author_rank: Frequent Contributor
timestamp: March 02, 2023, 10:07:34 am
content: As said. It depends on the desired application. There are many unknows - loading force, safety required, why not to use spring, will it be in slippery condition (teeth or smooth surface), should the material withstand aggressive fluids, should it withstand weather etc.You can simply take one hand clamp principle for linear movement, clock movement ratchet, ratchet for rock climbing or heavy duty car jack mechanism.For example if you are worried of rusting spring, than is high probability, that ratchet itself will rust to the pin and will stop working. If you want small loads or inspiration only than you can look tohttps://www.thingiverse.com/search?q=ratchet&page=1&type=things&sort=relevantfor example.