I am part of a second year team that hasn’t really done a complex lift yet. Is there any tips or tricks you guys have for building a reverse double 4-bar lift. If you know of a good tutorial video, that would be nice. Also, would a cascade lift work any better?
Honestly, just build it! You learn by doing! I went through 4 different iterations of DR4Bs last year before I arrived at one I was happy with, and I ultimately had one of the fastest lifts in the world by late season.
That said, if you have specific questions, of course feel free to ask them and we can help you work through them.
Also, be sure to check out good examples of DR4Bs before you start! Most good teams in Skyrise and ITZ had DR4Bs, so you can get a lot of ideas from them. See what they do differently, see what they all have in common, and adjust your design accordingly.
Good luck!
+12
I assume that you know the basis of how they work. You make a 4 bar, stick a gear on the end, then mesh it with a similar setup facing the other way. Just look up pictures and build a model, then work on stability and height.
Also, bar spacing is huge for height. Come back with more specific questions, and we’ll be happy to help!
So I will put some videos of great dr4b’s below, but I really don’t think that dr4b’s are necessary. They are hard to perfect, and you encounter a lot of problems. Although if you spend some time with it, and you get it working well, they would be great for this competition. Furthermore cascade lifts would not be a good idea because they are slow, and that is why i would be against them. You could easily build a 4, 6 or even 8-bar and do the same thing as a dr4b would. But its mostly you and your teams choice, if you feel like you are up to the challenge of a dr4b, then absolutely go for it. 
These were two great robots last year, although its ITZ, they are good lifts.
Skyrise, but again good
Bar lifts
Contradicting what i said above, it is a super fast cascade lift. But this is probably one of the hardest things to do, so i wouldn’t recommend it
Biggest thing I would recommend is don’t skimp on cross bracing! especially on the lower level stage 4 bar. it will be worth getting at least one or 2 5x c channels. this is the biggest issue I see with teams.
Next is not building a symmetrical 4 bar. this can cause the lift to lean heavily foreword or backward when overextending the lift.
the other big problem is gearing. there are lots of ways to do it and if done right you shouldn’t need a lot of motors. I wouldn’t be surprised to see single motor DR4B’s this year. DR4B’s are finnicky to build great. come back to the forum when you have a prototype.
Wait, what do you mean by this? what should it be like then?
@Fusion is saying asymmetry is one of the biggest problems, in addition to a lack of cross bracing. The DR4B should be symmetrical. Asymmetry will cause rotations, torques from gravity, and the like to not be the same on the two sides. As a result, that lack of symmetry will cause skewing, leaning, etc. This includes applying things like rubber bands symmetrically, not just building the sides symmetrically.
does this extend to the four bars? does the top four bar have to be identical to the bottom four bar?
Not really, but depending on what isn’t identical you may lose the linearity of the lift. You also may hit limits for the lift for one part before the other part has reached its limit.
Although side to side symmetry is very important, I was talking about symmetry between the top and bottom 4 bar lift system. In my experience, a DR4B that lifts close to linear is the way to go because you get maximum extension and keep your weight centered over the chassis.
In my opinion the whole system functions much smoother if everything is the same between the top and bottom lift so yes. there are some things that don’t matter as much, but bar length, and initial angle to the ground are very important to keep the same in my opinion. These things matter more if the size of the lift increases.