Hello, for an offseason project our team built an elevator. It works ok however it’s a little heavy using a #35 chain to both lift the carriage and the second stage. The biggest issue we have with it is that when descending quickly the chain can slack and the carriage can return a bit too slow for fast cycle times if this were going to be used in a competition. Currently we are only using a #35 chain attached to the mock chassis to lift the carriage and a single sprocket at the top. It uses only gravity to return to home. I’ve studied the Thrifty Bot dyneema pulley kit and it appears to work the same way in principle however in videos it’s way way faster/smoother even when run at an angle. I also looked at 1678’s swinging elevator from 2023 (awesome btw) that obviously can’t depend on gravity to return to position. What am I missing here? Even if someone could tell me what 1678s rigging from 2023 is called or if adding 2X the thrifty bot pulley rigging would solve our issues that would be awesome.
A) It appears to be a really tall elevator so it is going to take more time for it to travel.
B) IDK what it is but I would look at your gear ratio for your gearbox because a lower ratio means a faster elevator, but also high current draw so beware
C) I only see one point where bearings or rollers are keeping the elevator from wobbling back and forth and that side to side movement could definitely be slowing the elevator down
D) granted this is a offseason project but having the long chain set up in that way is going to restrict the amount carriage space you can use because you have to mount from the side instead of being able to use the entire carriage so you’ll have to offset and major mechanisms like pivots away from the chain.
The two common types of elevators are cascade and continuous. Both types can (and arguably should) be rigged to have a pull down.
If you followed the TTB design (and based on the picture you did) it looks like you are running cascade. 4272 has run both, and generally I find that cascade is more hassle free. You get some CoG advantages with continuous, but (in my opinion) it isn’t usually worth the hassle unless you have specific goals. I think 1678 was using continuous that year (could be wrong) but both can be very smooth if done right.
This is the common picture used to describe both. The cascade picture doesn’t have the full pull-down, but you have that figured out on your design.
As far as why your elevator doesn’t go as fast: #35 chain is pretty aggressive and heavy. I personally like using chain on the stage that doesn’t move (like you have) and then timing belt or rope for the other stage. Usually 25 is fine for that non-moving unless you are doing some really heavy lifting. Rope is nice because any center distance works (see the TTB elevator) but tensioning things and tying knots sucks. The TTB kit has some ways around that to make it easier. If you design it carefully, I find timing belt easier to assemble.
You also may have excessive friction from your 2x1 slides. TTB, SDS, WCP, Rev, and Andymark all sell different slides with different form factors. You may be a lot better off purchasing those if you can. They will run very smoothly.
Thank you for all the responses! We’re gonna try replacing the chain with dyneema for the carriage propulsion mechanism while we wait for TTB’s pulley kit to come in.
Can anyone say definitively if TTB’s pulleys/carriage rigging doesn’t depend on gravity to return the carriage to ground? Man I am struggling to see the commonalities between it and the continuous/cascade rigging. However with the spring offsetting the weight and how well it appears to work on youtube I would almost have to assume that it does not need gravity in order to return to home. In short we are looking for the ability to extend laterally if needed.
The TTB elevator does not rely on gravity if it’s rigged the way I think it is. Looking at your photo, I think your “cascade” loop needs an attachment to a crossbar at the top of the “0 or ground stage” in order to properly “transmit” the motion of stage 1 to stage 2. See sketch below, and let me know if my guess is wrong:
The thing that isn’t super obvious at first is the clamping of the dyneema cable which creates a fixed amount of cable on each end for both sides of your motion. In our setup this is done on the crossbar -
You’ll need the attachment point to be at the top of Stage “0” (where the cross bar would usually be. If you attach it to the bottom, Stage “1” won’t be able to travel upwards.
May suck, however this is a very minor thing that is easily learned. You can still use a turn-buckle if you need to. As far as knots are concerned: frc teams have figured out far more complex things than tying a knot in the correct spot… It’s not that hard.
Yup and a fid can be made out of a plastic drinking straw and some tape. Word of warning, getting splices to exact lengths is a chore and a half and requires a fair bit of practice, the 8-strand Dynema (7/64") often used in FRC (while plenty strong) is a pain to splice. 12 strand is FAR easier, but massive overkill strength wise.
In all seriousness though… just learn how to tie a proper bowline knot.
the rabbit comes out of its hole, runs around the tree, and goes back down.
Not that hard and one of the best knots to save your life.
It only sucks if you set it up wrong, there’s ways to make rope behave. Clamping the rope is not only an option, but usually best when available, because you don’t lose strength from a knot, and can change the length of rope in seconds. Various ratchet or turnbuckle tensioners also eliminate the need for re-tying knots, as you can just use the tensioner for increases tension.
Continuous is often less hassle actually, because you only need a single tensioner for the entire elevator, have a generally lower partcount, and you save a gearbox stage in most cases. You only really get one challenge for continuous, which is handling the sheer amount of rigging, but with attention to detail, isn’t too bad to work around. Cascade elevators can be very finicky when managing multiple independent rigging runs, all of which need their own tension while being synchronized off each other (doubly so when running cascade retraction, while continuous still only needs a single tension point).
If you do a Cascade elevator with belts tho, you can achieve a perfect center to center with no need for extra tensioning as you can increase the distance between the endpoints slightly from when the belt calculator gives you.
We made some makeshift brackets and a tensioning mechanism today using cable for a continuous system. It’s a million times better than the gravity pulldown. Thanks all!
