Help with gear rack mechanism

[Ocelot]

Hi all,

Long time lurker, first time poster here. I have reconstructed the mechanism shown here at 2:50 , and it works well; specifically, the way a 'clutch' gear is used to prevent the gear rack skipping once it has been pushed past its driving gear. However, I am having an unusually awful time adapting that mechanism for MOC purposes (it turns out to be quite sensitive to small changes in gear placement or size). Can anyone suggest a similar mechanism for me to try instead? (Or even the name of the mechanism that I'm looking for).

PS: Thank you; this forum is very inspiring!

 

Edited August 3, 2019 by Ocelot

[Jim]

Hi,

Welcome to EB!

You can include the video by pasting the url.

 

What is it exactly that you want to accomplish? Can you be a bit more specific, about the mechanism and your MOC?

[Ocelot]

Hi Jim,

Thanks for the reply. The video link was starting at 1:50 which was confusing. I've fixed it now. I didn't repost the video since you have that in your reply.

Details (my words are going to sound confusing, video clip at 2:50 explains it best): when a gear rack is driven upwards and the end of the gear rack moves past the driver gear, the end of the rack jitters and skips up and down since the driver gear is still turning (+gravity). This jittering motion is very unappealing. In the video, they use a 24 tooth gear connected to a friction pin to 'lock' the rack in the raised position; this works, but doesn't generalize well to other models/ different sizes.

What I'm looking for: Idea for a mechanism that raises a gear rack to predefined height, then keeps it fixed at that height while the drive is still connected. When the drive is reversed, the rack needs to retract downwards.

Edited August 3, 2019 by Ocelot

[Ocelot]

Update: I've managed to solve it! I'm attaching a picture of my (prototype) solution here in case it helps anyone in the future: as you can see, when the gear rack is pushed to the top, the gear driving it is stopped by red bricks, and the rotation is passed through the differential to the 24 tooth gear instead.Moving the friction pin gear to the fixed frame helped a lot.

 

gear_rack_small by Sal Ahmad, on Flickr

Edited August 3, 2019 by Ocelot

[skppo]

That seems a lot easier than the original design I have to say

[Gray Gear]

Additionally, you now cant break it by cranking it too far down, so your solition definatelly has some benefits 

[aeh5040]

Even simpler would be to replace the differential with a white clutch gear.

[Ocelot]

@skppo and @Gray Gear: Thank you!

 

@aeh5040: Absolutely, the simplest realization of this would be with an actual clutch gear. Unfortunately the white clutch gears (ones I have at least) require a fair bit of torque to slip, so they can't drive the gear rack directly. However, gearing down to the clutch (for eg, with input -> Z8 -> Z24 clutch + Z24 gear rack driver gear) does work; thank you!

The one (unexpected) advantage of using a differential is that one can chain these mechanisms together easily for sequential motion with only one input drive.