With the 2023 season approaching, its only fair to assume that next years game might be an elevator game for the 2020 and 2022 seasons have both been shooter games. With that, our team has taken up the task of designing an offseason elevator and with every elevator design comes the argument of cascading vs continuous. We have read through the many post about the pros and cons and people always seem to lean towards cascading over continuous, but when you look at top teams like 254, 1678, 2910, 1619, in 2018 and 1323, 3310 in 2019. All of these robots used continuous elevators.
We want to make a 2 speed elevator, (one for game pieces and the other for climbing) similar to 254’s, 2018 robot, and have the game piece go through the middle of the elevator. We have a LARGE amount of machining capability and a decently large budget. So, should we go with a cascading or continuous elevator?
In our messing around with both this pre-season, I think I like the simplicity of making a cascade, but I think that the continuous offers some small advantages if done well.
Let me explain: with cascade you have shorter runs of rope/chain/belt/whatever you use. This makes it less likely that things are going to bind. In 2019, 4272 didn’t know what they were doing with an elevator, but pulled off a 3 state cascade with some pulleys and springs from Menards. It worked fairly reliably.
Cascade is also easier to add constant force springs to, as you can add them to any stage, and it will help lift all the stages.
Third, cascade is predicable. You know where each state is at all times. With continuous, there isn’t a guarantee.
Now… continuous has some advantages with center of mass. Usually, a continuous elevator will lift the final stage first before the other states. Makes your robot less tippy for scoring game pieces in the lower goals, like the cargo ship in 2019. There are also some subtle advantages with pass-throughs, but this is very game dependent.
Honestly, if I were to recommend one to you, based on the description you gave, I’d run cascade. It’s basically November, so the simpler mechanics would help you perfect the elevator more. But … You won’t go wrong with continuous.
Another solution that may get some traction with the popularity of light brushless motors is controlling each state independently. This has many of the advantages of cascade as far as predictability, but has the added benefit of the low center of mass.
Whatever you can manufacture faster. With little more than a month left before build season, you have very little time to design, build, program, and test an elevator. Get something so your sub-teams can get experience with it, then if we do have an elevator this coming game, iterate on it if you have time.
If you’re making a passthrough elevator, definitely continuous. Because of how cascade moves, you’re not able to do a passthrough for a large range of its travel, as the stages are too close together. With continuous, it’s easy to do a passthrough everywhere except the middle of travel.
True, but only sorta. Continuous doesn’t control the middle stage(s) at all. If the friction and weight of the mechanism doesn’t come out in your favor, it’s easy for continuous elevators to block pass through unpredictably.
I’ve read about how some teams counter the stages moving unpredictably with Velcro on the bottom stage. It seems like you have some experience with unpredictable stage movement am I’m curious the solution to that problem.
Our 2018 elevator was continuous so we could “dunk” crates over the back at medium to high heights.
Our 2019 elevator was cascading so we could get 2x the torque on the middle stage that we climbed off of without sacrificing speed of the end effector.
Dual speed elevator, or anything for that matter, is fairly pointless since 2019. It’s neat to design and show off, but the effort is better spent throwing more in-stock brushless motors at the problem.
Using a cascade elevator allows you to put more force into the first stage while keeping speed in the other stages. We did this in 2018 and put hooks on the first stage for the climb.
Also the cascade elevator allows for a single loop (usually of chain for the base stage) so that you do not need to worry about managing the rope on a spool.
There is also a place for continuous elevators, and we have used those as well.
The decision on cascade vs continuous probably comes down what you intend to use the elevator for. If you use the elevator for more than just moving a lightweight game piece up and down, then there are a lot of good reasons to pick cascade over continuous.
At first I didn’t think the math added up but if you use 3 or 4 falcons you can get around 12 feet per second and still have the power to climb with continuous rigging. We stared with the idea of a shifter because of our shifting swerve we have been using for 2 seasons.
I agree with many of the responses here, and whether it’s a satisfying answer to your question or not, the short answer is that it will depend on your design intent, and your strengths and weaknesses as a team.
The difference between cascade and continuous rigging has some qualitative differences that you’ll have to consider.
Continuous rigging - Each stage is connected to each other using a continuous run of (usually) string, running from the winch to the top of the first stage to the bottom of the bottom of the next (so on and so forth). This means that the velocity of the final stage is equal to the tangential velocity of the drum. In 2019, my team found this type of rigging is easier to design than a cascade elevator, however, milage may vary.
Cascade rigging - The cable run her starts fixed on the stationary elevator frame, then wraps around the top of the first stage and is fixed with the next. This repeats with the start of each subsequent cable run attached to the previous stage. As previously mentioned, we found this the trickier design to make because the rigging was more complicated for our design and the return cables are attached in the same manner (in order to maintain the same up/down travel speed with a constant drum). Since each cascade stage is pulled up by the upward motion of the previous stage, the final stage velocity is equal to the tangential drum velocity * the number of moving stages. This allows for a higher final stage speed for a given gear ratio vs continuous, or a higher gear ratio for the same linear speed.
There are many more implications that I wont go into because others have already mentioned them. Overall it’s very important, to consider your design intent and goals when it comes time to choose.
We built a pretty close replica of 254’s 2018 elevator for the 2019 season. We are about a 30 minute drive away. Feel free to message me if your team wants to drop by our bay to take a look at one in person to see how they operate. We also have a 1/3 scale version a student built for a ROMI back in 2021.
There were a couple snags with slack in the rigging (especially under rapid acceleration), but by the end of the season we figured out how to address the issue without using springs.