I’ve seen all of them work extremely effectively, however, lots of people are trying to avoid using 6+ bars. Is there any competitive disadvantage in using a well made 8 or 6 bar?
I’m asking this because I’m worried that 8 bars will have an advantage over 4 bars that require additional modifications to reach the 30" goal in sack attack.
I shouldn’t think so. I am personally using a single central eight bar arm. I would say it’s equal to, if not MORE stable than two outside eight bars. I don’t think an eight bar or six bar would have any sort of disadvantage of a four bar. Eight bars can fit inside the 18 inch size limit and can reach far higher. In short, I see no downside. they all have different positives and negatives to using them. It just depends on your design I guess
I have a 4 bar that goes to 30 inches currently fits in 15in^3 If that doesn’t saysanything about needing an 8 or a 6 bar to do anything, I don’t know what does.
Mostly, it is because good 6 and 8 bars are hard to make, that’s why 4 bars are preferable. I would imagine that 4 bars are also more efficient because they are, in general, lighter. “Elbow” or “double four” bar 8 bars have issues regarding applied moment at some of their joints, but this can be dealt with.
We can currently achieve the goal with a 4 bar, however, my thoughts were that an 8 bar would require no modifications to our initial design and therefore would also be more efficient and on the long run, simpler.
Did you also have to add additional mechanisms to achieve this? Or is it just a long 4 bar?
What are the “Elbow” and “double four” bar designs?
None. Just a 4 bar. 
Running at the same rotational speed, a six bar (or eight bar) can reach the same height more quickly than a four bar. The difference may only be a second or so, but every second counts, especially in a game where descoring can drastically change the score in an instant.
Would the six/eight bar be achieved with the same torque? Or will the weight be increased since you’d have a longer mechanism?
Well our 8 bar design was very small. We never factored in torque because we are running at 1:25 already. Anyone else?
The mechanism wouldn’t necessarily be longer. In Gateway, we were able to reduce the length of our lift by using six bar. Of course, your mileage may vary. I won’t be participating in VEX this season, but based on my past experience, I’d be more concerned about whether or not you can lift enough game objects. In other words, a four bar might be a bit easier to lift initially, but that difference may become negligible when trying to carry a bunch of game objects.
How about a double reverse 4-bar? 
4 bars are far simpler than 6 or 8 (or even more) bar linkages. It is very possible to have a 4 bar linkage using just the long pieces of metal to reach 30". Sure, it may be easier to reach with a 6 or an 8 bar, but really, it isn’t that hard a challenge to do the same with a normal 4 bar.
I have seen 4 bar linkages with no modifications whatsoever that are also able to reach 30+ inches. For example, in Round Up, the team that won the College division, team aMEss (Massey University, Auckland, NZ) reached the 30" goals very comfortably with only 17.5" wide c channels as their arms. Finals Match 1 video.
Also, it can be very hard to build a well built 6+ bar, since at all the extra joints you potentially have a bit of wiggle room and extra friction.
~George
Just use “one bar”, in other words grab a 17.5in C-channel, connect a sprocket set up (2 sprockets attached to the piece 2 to the beginning of the arm, as the arm lifts the sprockets will remain aligned and the piece will stay in place) so that the piece you are lifting doesn’t turn.
Pros of one bar:
-4 times lighter than 4 bar.
-Easier to lift, make, and set up.
-It still reaches 30’'.
-Yields for faster ratio since it weighs less and the torque acting against the arm is much lesser.
Cons:
-Doesn’t reach as high as 6 or 8 bar.
We built an 8 bar … works well, not a problem that we have noticed as long as you use heavy duty gears
Would it be possible to use a chain lift this year? One of the winning alliances in worlds had a chain lift this year.
Yes. Why couldn’t one be used?
I don’t know. Everyone is talking about n-bars, so I figured there must be something wrong with the other arms.
Why can’t any other arm be used? Creativity is awesome if you can come up with something cool to use or find some cool linkage online that you like, Design your bot around it.
We are naming off different kinds of linkages that can get the job done thats simply what we are doing.
That’s the spirit!