What are the correct terms for linkages and lifts

[ASmith1675]

When first refers to a "4-bar" or "4-bar linkage" they typically are referring to the system you described, where one side moves parallel with respected to the fixed side. Like you mentioned, this is only one particular case of a 4-bar linkage. The lengths and orientations of the bars and pivots can be adjusted to create a wide range of motion.

If you are interested, you can do some research on Kinematics (I took two full quarters of classes in college on this topic), and specifically 2 and 3-position synthesis. These are design problems where you specify 2 positions of motion and determine the lengths and mounting of the other links.


The "stacked 4-bars" you are referring to are known as scissor lifts. They seem like a simple concept, but can be very difficult to execute well. They require a high degree of precision as the links need to lie in the same planes as well as have the same lengths to prevent the lift from leaning.

Hopefully this answered some of your questions.

[Chowmaster4695]

I'd like to point out that fore-bar linkages need not nessacarily have 4 bars.

[JeremyLansing]

Originally Posted by Chowmaster4695

I'd like to point out that fore-bar linkages need not nessacarily have 4 bars.

What is a fore-bar linkage? A quick google search turned up a bunch of results about four bar linkages (as well as this thread). I'm curious what you are talking about.

[EricH]

Originally Posted by Smitty1707

The "stacked 4-bars" you are referring to are known as scissor lifts. They seem like a simple concept, but can be very difficult to execute well. They require a high degree of precision as the links need to lie in the same planes as well as have the same lengths to prevent the lift from leaning.

The other term for a scissor lift, at least in FRC, is "What were you THINKING???" In addition to the degree of precision for the manufacture of individual links, they all have to go together precisely, and one end of the stack needs to be free to move horizontally, but not vertically. (This on top of the lift being rather unstable when fully extended--even a typical 26' lift can sway a bit when an average person walks from one end to the other while it's near the top of its travel.) Speaking as someone who uses one on a minimum of a weekly basis (and spent most of today on top of one), if someone successfully uses one in FRC, I will be quite surprised. (Current count of scissor-lift robots I've seen in elims: 1, maybe. On Einstein, 0.)

[Thad House]

Originally Posted by EricH

The other term for a scissor lift, at least in FRC, is "What were you THINKING???" In addition to the degree of precision for the manufacture of individual links, they all have to go together precisely, and one end of the stack needs to be free to move horizontally, but not vertically. (This on top of the lift being rather unstable when fully extended--even a typical 26' lift can sway a bit when an average person walks from one end to the other while it's near the top of its travel.) Speaking as someone who uses one on a minimum of a weekly basis (and spent most of today on top of one), if someone successfully uses one in FRC, I will be quite surprised. (Current count of scissor-lift robots I've seen in elims: 1, maybe. On Einstein, 0.)

Technically, 254's ball lift this year was a scissor lift... Just a very short single stage one.

[Abhishek R]

Originally Posted by Thad House

Technically, 254's ball lift this year was a scissor lift... Just a very short single stage one.

Does a scissor lift require the two parts to be connected in the center? IIRC, and please correct me if I'm wrong, but their pinniped was two separate mechanisms that acted individually or at the same time (so they could eject the ball out either end). If they were connected, they would never be able to remove the ball through their intakes.

[AdamHeard]

Originally Posted by Abhishek R

Does a scissor lift require the two parts to be connected in the center? IIRC, and please correct me if I'm wrong, but their pinniped was two separate mechanisms that acted individually or at the same time (so they could eject the ball out either end). If they were connected, they would never be able to remove the ball through their intakes.

Correct. The claptrap was two separate arms essentially, pneumatically toggled independently. No scissor.

[GeeTwo]

I have heard of the four-bar linkage with equal-length opposing edges referred to as a "parallelogram linkage", though I don't recall that I've ever read it.

[Boe]

Originally Posted by EricH

The other term for a scissor lift, at least in FRC, is "What were you THINKING???" In addition to the degree of precision for the manufacture of individual links, they all have to go together precisely, and one end of the stack needs to be free to move horizontally, but not vertically. (This on top of the lift being rather unstable when fully extended--even a typical 26' lift can sway a bit when an average person walks from one end to the other while it's near the top of its travel.) Speaking as someone who uses one on a minimum of a weekly basis (and spent most of today on top of one), if someone successfully uses one in FRC, I will be quite surprised. (Current count of scissor-lift robots I've seen in elims: 1, maybe. On Einstein, 0.)

In 2013 842 used two small single stage scissor lift to raise frisbees into their shooter
https://www.youtube.com/watch?v=4nHd_bG5dZE