Continuous vs cascade lift

[nitai]

hey!
part of our team project at the mechanic sub-team is to build a lift.
now we start to search for types of lifts and we got in trouble between continuous lift and cascade lift, we didn’t really found out what are the differences between them.
thank you for you’re help!

[Peyton_Yeung]

Continuous and cascade refers to the cable rigging on a telescoping lift.

In continuous rigging, a single cable spools to raise the output. This generally lifts the output stage first and once that is at the end of travel then the next stage goes up (assuming equal friction between stages).

In cascade rigging, each stage is connected to a previous one causing all stages to move at the same time.

[Alex_Y]

Its also worth noting that a well built continuous lift will perform about the same as a well built cascade lift. A N stage cascade lift can be though of as an N:1 upduction compared to a equally geared continuous lift. There are rarely cases where cascade or contentious superior to the other, and which type of rigging should be done really depends on the specifics of the robot design and game and team’s manufacturing ability.

Personally, I think continuous rigging is slightly easier and more practical in most situations. Continuous rigging is build due to only needing a single tension point to keep the rigging tensioned, whereas cascade rigging will need a tension point every stage. Continuous rigging can be ran with a lower gear ratio than a cascade lift to get similar performance saving a bit of weight. The main downside is that the spool has to spool up the entire length of travel of string, however this is very manageable with proper spool design (low fleet angle, grooves if you can manufacture them) to ensure only a single layer of string forms.

Cascade does have its merits however. Cascade rigging is easier to counterbalance with springs due to only needing to package the springs on one stage to counterbalance the entire system. Cascade rigging also has more force on earlier stages which in some games makes it a practical option to use the first stage of a 2 or 3 stage cascade lift to climb due to the higher effective gear reduction. Cascade rigging also avoids spooling issues if spool space is limited. However, it is difficult to run a retract string on cascade rigging. Different diameter spools can be ran but at that point continuous might be easier, or cascade retraction can be done but this adds significant complexity to the rigging.

[Patrick3357]

I greatly prefer cascading elevators for a couple reasons. First, as all stages move at once you have greater stage overlap and therefore greater strength/stiffness when the elevator is partially extended. If done well, the rigging can drive up and down without using any winch spools or spring tensioners to account for slightly mismatched feed rates. Rigging isn’t continuous so each individual rope needs far less turn buckle to tension. Meaning less retieing knots though-out the season, the tensioning is quick, tieing new knots is much slower and ropes typically need much more frequent tensioning shortly after new knots are tied. The long rope on a continuous elevator can be harder to route than the series of shorter ropes on a cascade. On partially extended continuous elevators the only thing keeping individual stages from extending in random orders is gravity, and sometimes friction can cause them to extend oddly ( final stage opens 50% then hits a tight spot and middle stage starts extending etc.) If you are unlucky, opposing sides of the same stage can start to rack and jam, racking can still happen in a cascading elevator, but it’s less likely. Not really an advantage, but it’s worth noting that cascading elevators can use different ropes for each stage as needs vary.

Overall I’d say that well designed cascading elevators are stronger, more reliable, more compact and their only downside is a little extra gearbox reduction (usually an extra stage in the planetary).

In 2019 and 2022 we used chain to drive the first stage and ropes to drive the other stages.

In 2018 we did have the cube gripper on a higher stage than the climb which gave us a small mechanical advantage, but even then, we used a shifter to go from place to climb modes if I recall.

[nuclearnerd]

We messed with continuous in 2019, before testing the whole thing out and going with cascade. There were two reasons for our shift:

1. continuous can’t control the position of the “intermediate” stages. That’s not always a big deal, but it was for our mechanism.
2. chain loops are easier and more predicatable than rope spools (which can suffer from unpredictable wrap and tangling). With continuous, you’re pretty much forced into rope spools. With cascade, you can have a simple chain loop on the first stage, and simple rope or strap loops on the upper stages.