Hi, a while back I created this thread about an idea I had for a Geneva mechanism using differentials. It had major problems with backlash though.

I've created a new version:

It's bulky and complicated but gives me hope that I can create another much more compact version.

I don't even really know how to explain it, it's basically the mechanism in my previous thread but doubled, with the second mechanism running in reverse and pushing against the first. The first output has a ratchet so they push against each other, creating tension and minimizing backlash.

The magical ingredient in this assembly is tension, so I believe it may be entirely possible with elements that have more slack such as standard diffs with gears etc.

I'll be working on some prototypes soon. For now there's proof that it works and in fact works rather well. Unfortunately it's large and not at all modular (limited to a 5:1 ratio without completely re-engineering it) but now that I've learned what works I can experiment with variations and hopefully can find something more practical. I believe I am on the verge of a great discovery here.

Edited December 24, 20213 yr by arieben

I have absolutely no idea what you are talking about or what this thing is, lol. Time to educate myself.

1:5, eh? Sounds like an easy gear ratio away from 1:10, which could be extremely useful for whenever I get around to making V3 of my base-10 mechanical calculator! I don't understand it either, but it looks very cool!

5 hours ago, 2GodBDGlory said:

1:5, eh? Sounds like an easy gear ratio away from 1:10, which could be extremely useful for whenever I get around to making V3 of my base-10 mechanical calculator! I don't understand it either, but it looks very cool!

If I go silent here and you want to mess around with this mechanism feel free to message me. In the meantime I'll try to draft up a better explanation for the whole thing.

22 hours ago, arieben said:

If I go silent here and you want to mess around with this mechanism feel free to message me. In the meantime I'll try to draft up a better explanation for the whole thing.

Alright, thanks! I'm not sure when I'll be looking into that project, but I'll let you know if I'm looking for more detail.

 

interesting mechanism, if im understanding this correctly you're effectively driving the output straight from the input but then use the differential to throw in some intermittent negative rotation to cancel the input rotation?

16 hours ago, markaus said:

interesting mechanism, if im understanding this correctly you're effectively driving the output straight from the input but then use the differential to throw in some intermittent negative rotation to cancel the input rotation?

yes! It's a glorified subtractive mechanism. much easier to build and understand intuitively than explain. thank you for that lol.

It reminds me the intermittent mechanism found in this old GBC Cardan Lift version :

In order to achieve the intermittent motion, any oscillating planetary mechanism (a differential is a special case of planetary mechanism) can do the trick.

As I observed in several designs (usually GBC modules), the simplest LEGO implementation of an intermittent motion (now found everywhere) relies on an eccentric gear. Examples : Torso's Cardan Lift,  Tomáš Ullrich's Draw Bridge, and countless of other designs.

But, with any of these solutions, because the output gear's speed changes continuously, it never stops completely : close to zero for a more or less long time, then high on a brief period (but I currently don't master the theory or the factors which govern the steepness of the transition).