I’m in the process of designing a robot for the 2018 game with all the tech we have in 2024, and have kind of run into a wall with elevator designs. Our team hasn’t built an elevator since I joined, so I really don’t have a great understanding of how they work.
I’ve gone through a ton of videos and threads explaining them, and I think I can understand continuous rigging based on diagrams, but I can’t wrap my head around how cascades work. I’ve also CADed out the practice cascading elevator on FRCDesign.org Stage 2, which makes sense to me but I think is missing some parts that many other elevators have that I’ve seen(i.e. CF springs) because the FRCDesign elevator is quite small(only extending to 34in).
As most people have seen firsthand, 2018 elevators are MUCH bigger and have to handle the weight of one(or two!) full robots in order to climb and score when the scale is tipped away. For this reason, I’ve tried to figure out how other successful elevators have worked and they’re generally rigged very differently to the FRCDesign elevator. In particular, 4414’s 2023 elevator and 2910’s 2018 elevator have been two that caught my eye. After reading(and not understanding) 4414’s writeup on their elevator and trying to see 2910’s 2018 CAD(the STEP and grabcad links aren’t working for me ), I decided that it’s probably better to ask CD rather than trying to piece together a bunch of really old and really new information.
Question Barrage:
What are the pros and cons of running different rigging styles? My understanding right now is that cascade is more common and easy to assemble, but continuous offers some benefits in the final stage torque department because cascades half their torque and double their speed with every stage. Also, am I right in saying that cascades actually only drive their first stage and the rigging sort of handles the rest by using fixed cable lengths to pull up their other stages?
What are the pros and cons of different driving methods? Right now I see 4 main options: Full cable, full chain, full timing belt, or some frankenstein of these(EX: the FRCDesign elevators, which have the 1st stage chain driven and the rest with dyneema)(which seems to be a common way to do elevators).
How important is counterbalancing your elevator? CF springs seem to be very common, but I don’t think I heard of any robots running them in 2024. Is counterbalancing a must for a heavy duty elevator like one for 2018, or have super powerful brushless motors made them nonessential?
How is rigging actually physically done with these different driving methods? As someone who wasn’t very involved in the construction of our robot last year, rigging seems a lot less straightforward than assembling other mechanisms. As far as I can tell, with full dyneema, you attach a spool to your motor, belts and chains you obviously use pulleys and sprockets, and frankensteining is weird. Whatever you use to drive is then run up and down your stages to pull them up and down. There also seems to be rigging done inside and outside of elevator tubes(not sure what the pros and cons are there).
Side question based on the previous one: 4414 said that their 2023 elevator was very low maintenance, and was a continuously rigged belt elevator. What makes this kind of elevator special and is it a significant improvement over other rigging types?
Obligatory:
I likely won’t try to replicate any of these top tier elevator designs for reefscape even if it does call for an elevator just because we haven’t built one ourselves yet. In that case we’d probably snatch a GreyT elevator and call it a day
Hello! I’m in the opposite state of you, I only understand cascade elevators but have basically no idea about continuous.
For cascade, I recommend starting with the FRCDesign elevator design. Driving the first stage with chain and second with dyneema isn’t too difficult, and tensioning both is fairly straightforward (turnbuckles for chain, CAM for dyneema). Other designs add a bit more complexity, so starting with the FRCDesign/TTB-WCP Frankenstein is a good intro.
We counterbalanced with CF springs this past season, mainly because we used our elevator for climb. Depending on the weight of the elevator and cube scoring system, I’d add CF springs, but if you are climbing you’ll most likely be using them. I’d guess the reason many teams didn’t use CF springs in 2024 was because they didn’t climb on their elevator and used light amp/trap scoring mechanisms. IIRC 5940 ran CF springs for their climb so they could climb/trap with it.
I ran into this same problem, but the chain-dyneema setup makes this pretty simple. The chain is attached to the first stage, and lifts it up. As it does so, the dyneema between the top of stage 1 and the carriage/stage 2 shortens, raising it up. Internal rigging saves some space, but from what i’ve read it’s a lot harder to maintain and build.
We used a continuously rigged belt elevator in 2023 (pictured), and it was easy to maintain. However, it often broke (mostly REV bearing blocks, but at Fort Worth the belt snapped). I don’t fully know how to design one, but it allows for clean packaging (all belt is to one side or within elevator) and doesn’t require any maintenance (if done well).
While elevators aren’t too complex, they are easy to get wrong. So, after using continuous belt in 2023 and cascade chain-dyneema in 2024, i’d recommend the chain-dyneema TTB-WCP crossover (or avoiding an elevator altogether).
Continuous requires less reduction in the gearboxes, since the final stage moves at the same linear speed as the drive belt/chain/rope. This isn’t a big deal with a 2-stage, but it matters more with 3+ stages.
However, it makes a big difference if you’re trying to do two things with your elevator – as was common in 2018. In that case, the fact that your first stage is moving at half the speed and twice the torque of the second made it possible to elegantly use the same elevator to lift cubes (with the last stage) and climb (with the first stage only).
Anyway, rigging…
Continuous and chain don’t go together well; the chain is excessively heavy and the long length means chain “stretch” matters more.
Continuous and rope don’t go together super well, although they can be combined; a capstan or drum is more effort to get right (search for discussions of “fleet angle”) – for accurate control, you have to ensure that the rope spools in a single layer, or you need a capstan system that isn’t available off-the-shelf. This stems from the problem of needing to attach to many points along the first stage rigging (e.g., teeth on sprockets meshing with chains or belts).
Continuous and belt work great; the belt is light and flexible (small-ish bend radius), and low-stretch. That means running a bunch of it up and down the elevator for the different stages doesn’t add too much weight or space for the pulleys.
Cascade lends itself to hybrid rigging methods (as TrevJag mentioned) because each stage gets its own rigging. All of that pain with capstans or spools for rope? Irrelevant for the second or later stages of a cascade. Chain is heavy? For those stages, you only need to grab two points on the loop, instead of needing to engage at many points, which is the whole point of using chain or belt. You can even mix and match drive positions: one centered chain for the first stage, multiple ropes at the sides for your subsequent stages.
True counterbalancing is much easier and better with cascade elevators, or single-stage elevators. This is because all stages move together, so the counterbalancing can just be applied to one of them, and will affect all of the others.
HighTide employed an “anti-counterbalancing” scheme in 2023, where they used CF springs to hold the intermediate stages down until the elevator was fully-extended. This meant their CoM stayed lower when performing partial extensions; only the required stages extended; the rest stayed collapsed. This is something you can only do with continuous elevators; cascade elevators move all stages at the same time. If your intermediate stages are heavy enough and the friction is low enough, this happens for free. However, as soon as something binds, you may have a random intermediate stage extend. This problem is far worse if you try to counterbalance each stage individually in a continuous elevator; you don’t know which stages are going to move at any given time. In short, I wouldn’t recommend trying to counterbalance a continuous elevator, unless it’s extremely heavy and you’re only trying to take up some of the weight.
One advantage of counterbalancing in this era of many-powerful-motors is that it makes your maximum up and down speeds more closely match.
The disadvantages of counterbalancing include making the elevator worse for climbing, safety hazards (stored energy, both out-of-match and in-match – if the robot falls over), and general complexity.
I mostly covered hybrid rigging of cascade above. Here’s the gist, though: the first stage is a rotary-to-linear converter; you’re trying to make a motor extend the elevator. You want a loop so you can drive the elevator both up and down.
Each subsequent cascade stage is a force-direction-reverser: you have the linear motion already, but it needs to cause movement in the opposite direction. The fixed point is the top stationary spanning bar; from the point of reference of your first stage, it’s moving down. This is probably the most confusing part of cascade elevators. You can also think of it as being a 1:2 increaser, which is what you get when you have one end of a rope fixed and you move the sheave. Again, you want a loop so you can drive the elevator in both directions.
There are various topologies that work, but they mostly boil down to “which direction are the pulley axes pointed?” and “where along the elevator do you position them?” Some combos are possible to position inside the tubes, which is how you get that. You’re best off looking at examples. Then, there’s tensioning, which always involves “how do you make the length of the flexible drive thing adjustable?” Chain turnbuckles, belt clamps with screw adjusters, regular turnbuckles, cams, dyneema lashings, etc…
Continuous rigging is a back-and-forth deal. Again, go look at some examples and you’ll see how it works. It’s one big loop instead of a bunch of smaller loops, though.
In their case, I believe it was generally that the system was well-engineered, and that they used high-quality belting.
For what it’s worth, our scrappy 2023 cascade-rigged elevator was also low-maintenance; once we got it tensioned up, it pretty much stayed tensioned.
It’s easier to list common failure points and try to nip those.
One is: if your elevator tries to force the belt/chain/rope to change length, you’re going to have a bad time.
The two most common ways for this to happen are to have a fixed mounting point (e.g., that chain-to-tube mount used in The Thrifty Elevator, or the rope clamps) that isn’t quite placed along the axis of motion. When the clamp moves, it tries to stretch the chain/rope/belt to the side, and usually stretches the elevator top and bottom pulleys/sprockets together as a result. This sometimes results in plastic deformation of the elevator and de-tensioning as a result. Then, you tension it back up and it happens again. High-maintenance.
The second common way this can happen is by positioning a moving pulley such that a belt/chain/string run isn’t parallel to the direction of motion, so a fairly similar problem. This is most common in a continuous elevator where the pulleys are larger in diameter than the distance between the belt runs, such that the belt needs to run diagonally every other turn. In this case, it’s the same end result: the elevator tries to force the belt/chain/string run to change length, but instead, it deforms the elevator. The key: when one of the runs needs to be “diagonal”, it should be the run between two pulleys that are attached to the same structure and always stay the same distance apart, not two pulleys that move with respect to each other as the elevator extends. The run between two pulleys that move needs to be parallel to the direction of motion.
Finally, the biggest problem with elevators is connecting to electrical or pneumatic components that are on the moving part. With arms, you can kind of phone this in, but with elevators, you need to plan out your cable management from the beginning. It’s not an electrical component; it’s a mechanical component that participates in the electrical system. Energy Chain can be the way, but the kit stuff is usually too small. Coiled cable and coiled tubes can work pretty well, though coiled cable is expensive and is harder to find in 12 AWG. This problem is the worst because it bites you even if you buy a COTS elevator.
Thanks for the super detailed answer! Are there any other tips you have for planning the wiring on an elevator? I haven’t payed a ton of attention to the different wiring techniques for the elevators I’ve looked at?
Minimize how much you are sending up there is the first rule imo.
This is an excellent exercise in "picking the correct hardware " not everything needs a big old brushless motor. Servos and pneumatics (with their own gotchas of course) can sometimes be a way cleaner solution than a regular motor and gearbox.
Agreed. My favorite optimization is a brushed motor, like a RedLine, on a 30A breaker, since you only need two 14 AWG wires. With the addition of a 2-, 3- or 4-conductor signal cable, an encoder or limit switch is also pretty doable. However, if you are connecting to a brushless motor, the 3x stator connections plus 6x encoder are worse than 2x power, 2x CAN (or PWM!) and putting the controller up top in most cases. This is especially true if you plan to use a limit switch that could connect to the motor controller or CAN bus instead. If you do take the plunge and send CAN up your elevator, definitely put the terminator up there; the only thing worse than sticking your CAN bus out on an elevator there is doing it twice.
Pneumatics can be great if you can get away with a single-acting cylinder. Otherwise, you’re probably running a pair of 1/4" OD tubes, and those have a min bend radius bigger than even a pair of 12 AWG wires.
That said, once you’ve figured out how to get one thing up the elevator, you’ve done the bulk of the work; it’s less complex to upsize whatever you’re using for more wires/tubes.
), I decided that it’s probably better to ask CD rather than trying to piece together a bunch of really old and really new information.
