The lift is an essential part of any robot that has to pick parts up. Lift come in two main varieties: rotational lifts, which operate by turning arms, and linear lifts, where the claw is lifted strictly up.
The simplest lift is the arm, where a long C-channel (usually 35 holes long) is turned from one end using barlocks or the holes in gears, so that it spins and causes the claw to go up. Arms typically require a wrist at the end so that the claw does not move, either.
Arms, however, are often wobbly and wrists are a waste of a motor. This lead to the invention of the 4-bar; a design featuring a parallelogram which allows the claw to maintain an orientation parallel to the floor.
4-bars are often paired side by side, for additional stability. Note, however, that 4-bars are much heavier than arms, although this weight will likely be much smaller than that of the claw, and offset by the additional motor gained by not having a wrist.
Another flaw of the rotation-based designs are their limited height. Arms and 4-bars can’t go very high, although occasionally the height is sufficient. When it isn’t, teams sometimes build n-bar lifts, with n usually being 6, but theoretically being capable of being up 10 or 12. Each additional pair of bars increases the height further, but adds more friction and weight.
Vertical lifts tend to diverge drastically in how they do things. The best-known vertical lift is the scissor lift. The scissor lift consists of two linked stacks, each powered separately. Each stack consists of two C-channels back-to-back, connected by a pivot in the middle.
There are three main ways to power scissor lifts, the first being to push the bottoms closer together, the second being to turn one bar relative to the other, and the third being to use some other vertical lift to push the bottom joint up, causing the scissor lift to act as a height multiplier. Scissor lifts are useful for the large amounts of weight they can lift.
Rack and pinion lifts are the simplest vertical lift. They consist of a line of rack gears on the back of a linear slider, and a motor with a gear that meshes with the rack gears and can slide freely on the linear slider.
The third type of vertical lift is the elevator, or chain, lift, which comes in two varieties, continuous and cascading. Continuous elevator lifts can operate with either winches or high-strength chain. Low-strength chain will definitely snap, don’t use it.
The continuous lift works by pulling the chain, which pulls the top of each stage closer to the bottom of the next stage. The chain is connected to the claw, so it lifts things instead of spinning wildly. Cascading lifts work differently; they have a separate chain for each stage. Each chain is connected to the top of the previous stage and the bottom of the next, this means that when the bottom stage goes up a little bit, the next stage lifts twice that high. Elevator lifts are good for relatively quick vertical lifting, but often have problems with slack and instability.
Sometimes, you can combine two different lifts, to get the benefit of both, or to go higher than normal. One such lift is the double-reverse 4-bar, which consists of a 4-bar lift, on top of a 4-bar lift in the opposite direction. The two are usually mechanically linked, so they lift at the same rate.
The double-reverse 4-bar is the fastest lift by far, and also lifts extremely high with long enough bars - it was the dominant lift used in skyrise, where robots would lift 5 feet.