Cascade VS Continuous Elevator

With the overall theme of 2020 being “Rise The Force is Building”, it can probably be deduced that there will be some form of stacking involved in next years game. With the last post being over 6 years old (Dec 2012) and as we now have access to new technology not available or uncommon back then (3D printing, neos), I was wondering the pros and cons of the two elevator types. My team has used a cascade elevator for the past 2 years but noticed that some powerhouse teams use continuous instead and wondered what the benefit was over cascade and if the said benefit was worth the risk of creating a new elevator design. Or maybe I’m just wrong on the whole access to new technology thing and the old post is still just as relevant in which case whoops

God please not another elevator game

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3 elevator games in a row would just be ridiculous.

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I think the best way for you to find answers might be to search “cascade continuous” or similar in the CD search bar. I found a few other threads where this was discussed. I would like to here more recent thoughts after the past two seasons, though.

Maybe the following poll would be in order? Vote based on what type of elevators (if any) your team built on it’s competition bot.

  • We built only cascade elevator(s) over the past two years.
  • We built only continuous elevator(s) over the past two years.
  • We built both continuous and cascade elevators over the past two years.
  • We did not built an elevator over the past two years.

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Also, I doubt next year will be a game that encourages elevators.

With the cadathons and the last 2 frc games and the offseason projects and etc etc, personally I am VERY tired of cading elevators

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I’m tired of elevators. I want a game with having to throw bowling balls.

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As awesome as this would be, FIRST wouldn’t let a dangerous or impossible to test object be the game object.

Dangerous! We’ll wear safety glasses won’t we? It’ll all be fine.
Although I would like a game with shooting something like fuel, or maybe discs or footballs.

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I agree. A shooting game is definitely something we haven’t seen in a number of years. This game however just doesn’t sound like a shooting game and that’s unfortunate. Perhaps a sorting game?

Back on the original topic, regardless what next year holds our team is looking to do some learning on building elevators. The first one we built in 2018 literally ripped itself apart and I don’t foresee elevators ever going away forever even if we don’t need them for 2020. So I’m interested to see what the general consensus is on continuous vs cascade.

Also dumb question, the difference between the two is whether you’re using one long chain run or different runs for each stage, right?

I’d also be interested in seeing what people think of nested vs…not nested? I guess the word there would be cascade but different meaning. Basically, whether to stack stages in front of each other or nest each stage inside of the one before it.

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A continuous cascade has a single, long cable snaking throughout all of the stages. Often, this means making custom pulleys, or sourcing a COTS option. We used aircraft cable in 2018, as we needed the strength for our double climb. It stretched, and frayed and let me tell you- you DON’t want to be checking something on your bot and suddenly get an arm full of little metal splinters. Not fun.

Conversely, a cascading elevator uses a “cascade strap” to link the movement of the second stage to that of the first. Most teams use a thin chain, but it’s also possible to use belting. The cascade can be any variety of things, but most teams seem to use a strip of webbing (we used a ratchet strap) or some sort of rope.

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One big factor to consider is how much torque you need on your final stage. With continuous elevators the torque is the same for every stage of the elevator but with cascade elevators each stage will have half the torque but twice the speed of the previous stage. This is a problem we ran into in 2018 when we tried to add a climber to our cascade lift.

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We ran a 2-stage continuous elevator in 2018 with one rope run in the center of the elevator. In 2019, we used a 2-stage cascading elevator with 2 1/8" Dyneema rope runs on each side of the elevator. We had to use two pull-up runs instead of one in the center due to our passthrough design. Neither of our elevators had pull-down runs or CF springs.

One thing to keep in mind is the center of mass. Because all stages move in a cascading elevator, your center of mass moves upward more quickly than a continuous elevator when extending (although we did not have problems with this phenomenon this year).

From a programming standpoint, both elevators are equally as easy to program with respect to encoders and preset heights.

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One challenge with continuous elevators is that unless you add some extra latching mechanisms (which I’ve seen), you can’t be guaranteed that the carriage won’t lift the intermediate stage (by friction) before it hits the top, which might cause interference if you flip over it or through it.

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This may be a niche consideration, but (assuming your robot is max height) at the start of a match your cascade elevator stages must be lowered all the way to stay within the height limit. A continuous elevator stage could start at any point in the first stage of movement.

Could save you from having to move the elevator in auto, but I wouldn’t design specifically for this

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We used velcro on our continuous elevator this year to fix this problem we just added and removed it to the bottom of the second stage depending on our friction and our power

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I wish our team didn’t scrap our 2018 practice bot so we could have looked at ways of making our cascade elevator better. Plus we could have converted it to a continuous elevator and learned even more about elevators.

We ran a cascade elevator last year and a continuous elevator this year and the reason we switched from one to the other really just revolved around a specific feature we were trying to design the robot to be able to have… As far as controls are concerned I would recommend cascade as being easier to get consistency with… as you don’t have a sudden change in load as you go halfway up.

Like 5190, we also switched from a continuous elevator in 2018 to a cascade in 2019.

Our 2018 elevator was a 3-stage nested design based on the Andymark elevator brackets and 1x2 aluminum tube. It was rigged with two continuous runs of #25 chain (one each side), since it was intended to be our climbing mechanism as well as lifting our cube claw. That means that it did have a classic return (pull down) path for the chain, since that’s necessary if you expect the elevator to lift the robot. It worked moderately well for lifting the claw, but due to too much flex in the system did not provide for a good climb (the drive chain slipped under full load, no matter what we did.) It was also fairly difficult to rig and required continuous adjustment to keep it working properly, as well as being very slow due to a high gear ratio on the motor (64:1 planetary on a CIM, since it was meant to lift the robot.) It was not our most successful design.

This year’s elevator was a stacked 4-stage using 1" t-slot extrusion and plastic t-slot glides from 80/20, with the two stacks of extrusion only joined by the face frame that held the mechanism. It was cascade rigged with 3/64" extra-flexible aircraft cable, tiny pulleys from McMaster-Carr, and eye-bolt tension adjusters at the lift point of each cable. We still used two sets of cable runs (one on each side) since our hatch mechanism was very long and ran up the center of the elevator stack. It was powered at the bottom by two reels on one shaft, run by a 775 in a VersaPro 25:1 gearbox. No return line was used, since it only had to lift the mechanism up and we could depend on gravity for the return. It proved extremely fast and reliable, so much so that we were able to make a pure hatch-bot competitive (along with one of the best hatch mechanisms out there.) It was also much lighter, more stable, and cleaner running (i.e., no jams or shifting out of true) than our previous design.

I can’t say that we’ll never try another continuous elevator, but for most applications I can’t imagine we’ll use anything but a cascade design that builds on this year’s very successful one.

I’ve seen this concern listed before, but we’ve never come close to encountering it with our continuous elevator (in 2018 and 2019). I’d be interested in looking at a design that had this issue to see how the friction/binding occurred to lift the intermediate stage. Gravity usually holds it down.

I was initially hesitant during our first continuous elevator mechanism build in 2018 because of concerns listed on CD, but it came out smooth as butter. There are a lot of good designs and resources out there.

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