Zipped STEP attached.
For context, I have zero experience with elevators. I took what advice I could from other CD topics and published elevator designs (1678, COTS elevators, etc.).
The 2x1 extrusion the motors and bottom piece of the elevator are mounted to is part of my team’s [more-or-less] perennial tank drive frame.
Features/choices:
Continuous rigging, driven by chain (bolts through the chain links, similar[ish] to Thriftybot’s design. I forgot to add the bolts, but their [clearance] holes are there at the bottom of the moving 2x1)
2 NEOs on 12:1 CIM Sports for 1.5s lifts, minimal current draw
Tightening eyebolts for cable tensioning
Skipping the 2x1 across the elevator in many designs in favor of churro standoffs/the orange hexshaft.
Thriftybot bearing blocks
Around 7.5ft of traverse
Designed for 2018 height limit (would be ~0.5in under if mounted to previously mentioned tank drive frame)
I think you’d get better/faster replies if you posted pictures of the elevator from various angles or a grabcad/onshape link. A lot of people are out for the holidays and opening a CAD file is a bit of an extra step.
In addition to that, what are your current machining capabilities? Depending on this some answers may change.
GrabCAD link [has screenshots]: https://grabcad.com/library/elevator-cad-2
Current machining capabilities: 3 axis CNC router [24x48in], drill press/bandsaws, 3D printer (Stratasys UPrint or something like that).
It is an aspect to be aware of. If you needed to have a powered retraction then you would redesign for that purpose. It may also impact position control and chain tension. Some approach with return springs and some with a winch. If you use a winch then you need to synchronize with the extension chain.
I’m confused. You are using chain and cable for continuous rigging? Typically using 2 different kinds of rigging like that would be cascade.
Also, while not entirely required, driving the elevator down is a good idea - especially with the TTB and Greyt elevator being driven down. This is going to help keep the rope tensioned and may also make your elevator faster since you don’t have to weight for gravity and friction to help you down.
I’ve seen teams be successful with only driving their elevator 1 way, but with modern COTS, this feels like disadvantage.
Got it. Cascade rigging isn’t too hard, so I’m sure you can figure out how to power it down.
In 2019 we did all of our rigging of a 3 stage cascade with pulleys and springs from our local hardware store and normal rope. While I don’t recommend our method, our 2019 elevator was fairly effective. You’ve at least had the foresight to plan the rigging in CAD (unlike us), so I’m sure you’ll get it.
Do you have a BoM showing the price your design would cost for your team? I am skeptical that your custom additions will save a meaningful amount of money, especially considering the performance sacrifices being made.
I don’t currently have a formal bill of materials, though some back-of-the-napkin math I did earlier showed it would save a couple hundred.
What specific performance sacrifices are you noticing?
The few-hundred dollar figure was using custom bearing blocks replicating Thrifty’s (essentially, machining something functionally identical to theirs out of aluminum with our CNC, then doing the zip tie slot on the back with an angle grinder. We’d have to skip the bits that stick out the back and on to the sides if the 2x1).
Whole lot of stiffness issues. I can see a lot of bowing, bending, and breaking going on, primarily on most of the custom components. Assembly looks tricky at best and downright annoying at worst, with maintenance nearly impossible in some areas. The hex/churro tube replacing the 2x1 gives you nothing of value while being noticeably less stiff, and there doesn’t appear to be any way to connect many of the components outside of welding (and you should not be welding your elevator closed). The elevator doesn’t appear to have a bottom to rest on and it seems like you’re investing more time and resources into making this elevator work than you’re likely going to get benefit out of it.
My hot take for the day: It is really, really hard to make a good elevator design that is cheaper than the kits sold by venders, and therefore if you cannot afford to purchase an elevator kit, you are better off not using an elevator and investing your money instead into other mechanisms that are less resource-intensive for your team.
I should clarify - I give props for this being your first elevator design. There’s a lot that’s done right that I haven’t listed, since you specifically just asked for the issues. Keep practicing and keep iterating. If I were to make a suggestion - take the COTS components of a Thrifty or Greyt elevator kit and design your own elevator using those components. It will not only be a more viable elevator design to use in-season, but it will also be better practice for designing elevators as it will solve more of the difficult problems for you, allowing you to focus on designing the elevator to fit your specific requirements and integrate it into the rest of your robot design.
I just did a quick mock up so don’t judge the dimensions too harshly but you could copy thrifty’s pretty quick. As said above you lose the tabs on the back to square it on the 2x1 (which are nice but honestly not necessary). Then the center holes could be made a little bigger and the zip tie could just be a little longer and go through the 2x1 (a little annoying but not a big deal). the center bit is 3d printed. holes have 1/2" spacing to fit common designs.
Can you point out where in particular you’re seeing the bowing/bending/breaking/assembly difficulties? I’m not doubting you, I just want to know where to improve.
I did forget to mention this, but there would be a few L brackets in there that I skipped CADing earlier in the process and then forgot to add them when I was doing finishing touches. Same with a bottom to the mechanism.
That’s an entirely valid take. We will be seriously considering a COTS elevator if the game lends itself to it.
Thank you!
I haven’t listed specifics since I’m at work right now, but once I get some time I’d be happy to go over the overall design with you if you’re interested.
Sorry to dash your hopes but this was the CAD equivalent of napkin math. I don’t think my team will be going with this idea or even try it. It was simply made to convey an idea with only 10 mins of thought put to it.
However, if anyone does take inspiration from it tag us. It’d be cool to see.
