A Very Simple Lift Analysis

VEX V5 General Discussion Technical Discussion
1

I don’t see any of those lifting to heights of, let’s say, 12 feet. Neither this thread nor the one I posted in earlier exclude heights like that. Being trained professionally as a scientist, I find it very disconcerting to see a whole group of comparable height examples used to show a method is the fastest for all heights. It’s like swinging many pendulums with amplitudes only up to 5 degrees, seeing they’re all very nearly simply harmonic, and then claiming pendulums always undergo simple harmonic oscillation without having tried much higher amplitudes which would have shown this to be a false conclusion.

I wouldn’t disagree with you for these lower competition heights. My post elsewhere about the utility of a scissor lift was specifically questioning about pushing to much higher heights and about the simplicity of locking it down well for safety. The DR4B will need arms around 6 feet long, so at very least there is no way it will fit in a small length/width region, which is something the scissor lift can still do. If I get the opportunity soon, I’ll try to build two very tall lifts to compare them. It would also be good to build two (or more) stacked DR4B (QR4B?) to improve the comparison. Even with aluminum, this is going to take a lot of motors and rubber bands. Hopefully someone can get this done before I can.

Maybe the DR4B will still be faster. Maybe not. But until I see something a lot higher, I’m not buying such a general conclusion from such a limited set of example heights. Statements that people like me who recognize that the “blanket evidence” really isn’t because it is severely lacking in breadth and so are holding off on judgement until we have a better set of evidence are “ignoring or not accepting” bother me. Some people probably are “ignoring or not accepting” such evidence. But some of us are very careful about sample sizes, breadth of the sample, and extrapolation.

2

I don’t see any of those lifting to heights of, let’s say, 12 feet. Neither this thread nor the one I posted in earlier exclude heights like that. Being trained professionally as a scientist, I find it very disconcerting to see a whole group of comparable height examples used to show a method is the fastest for all heights. It’s like swinging many pendulums with amplitudes only up to 5 degrees, seeing they’re all very nearly simply harmonic, and then claiming pendulums always undergo simple harmonic oscillation without having tried much higher amplitudes which would have shown this to be a false conclusion.

I wouldn’t disagree with you for these lower competition heights. My post elsewhere about the utility of a scissor lift was specifically questioning about pushing to much higher heights and about the simplicity of locking it down well for safety. The DR4B will need arms around 6 feet long, so at very least there is no way it will fit in a small length/width region, which is something the scissor lift can still do. If I get the opportunity soon, I’ll try to build two very tall lifts to compare them. It would also be good to build two (or more) stacked DR4B (QR4B?) to improve the comparison. Even with aluminum, this is going to take a lot of motors and rubber bands. Hopefully someone can get this done before I can.

Maybe the DR4B will still be faster. Maybe not. But until I see something a lot higher, I’m not buying such a general conclusion from such a limited set of example heights. Statements that people like me who recognize that the “blanket evidence” really isn’t because it is severely lacking in breadth and so are holding off on judgement until we have a better set of evidence are “ignoring or not accepting” bother me. Some people probably are “ignoring or not accepting” such evidence. But some of us are very careful about sample sizes, breadth of the sample, and extrapolation.

3

What do you need a 12 foot lift for?

4

From some game analysis, one can reasonably conclude that one only needs to be able to stack 13 cones high on each mobile goal to be guaranteed victory (if you have questions about how I got that figure, please PM me). Keeping that in mind, we can calculate the lift size that we need to achieve this. Using specs from the Game Manual (again, ask to clarify), the formula to figure out the height of a stack is:


h(n) = 8.87 + 2.75n

Where


n

is equal to the number of cones in a stack. Now,


h(13)

is


44.62"

, and let’s give that 3 inches margin, because you have to go ABOVE the stack. So, one can conclude that the tallest height one needs is


47.62"

Knowing these limitations, we must consider the additional challenges this game provides. I agree with you that, from what I can tell, reverse double n bars, are the fastest and most efficient. But, I think you’re jumping to conclusions by considering only those criteria. To build a reverse double n bar to that height, one needs to give a massive amount of space on your robot. Consider @antichamber 's robot, for example. In his most recent post, he showed off the cone intake on his robot. By doing so, he also showed off his rd4b. Look at how much of his 18^3in cube he is using to lift the tiny cone. An easy ~80% of his robot is used to lift one of the smaller game objects in recent history (excluding NBN balls, but those are another story). This is my biggest criticism of rd4b and families: that they are incredibly space inefficient. In a game like Skyrise, where all Game Objects need to be lifted to ridiculous heights, and everything can be done on the single lift this is fine. But in this game, we (1) only have to lift to 48in, and (2) we have to lift cones to stacks and lift those stacks into zones (if you’re scoring the better way), which has vastly different speed and torque requirements, thus requiring two different lifts (unless you’re really crazy, and put a transmission on your lift :)). I don’t care how great of a builder you are, you will not be able to build 2 different rd4bs in one 18^3 cube, or at least, not 2 where one can extend to 47.62in.

While I concede that rd4b have been proven to be the fastest lifts, they are not by an enormous margin, and in a game like ITZ, where there are contested game objects, more important than manipulation speed is drive speed. Even at the highest levels of play, you can see that robots with the fastest drives (and the best drivers) always do well. Robots in this game will be driving most of the time, to get to the game objects they need. And when it comes to driving fast, and incredibly important decider is weight. Another mark against rd4bs (and related to size), is that they can be heavy compared to similar lifts.

Shall I go on?

5

Drop balls through basketball hoops, reach to the 2nd floor from the lobby of a school building, etc. There could be reasons to lift this high. The OP says a DR4B is the fastest lift to do it based on lots of much shorter lifts. I’m not sure about that, reserving judgement until I see something comparable.

6

@callen, I think the OP was referring specifically to competition lifts. In the real world scissor lifts are very useful for reaching high up places, but in the real world they also have access to hydraulic actuators, so…

Even though what the OP seems to be speaking generally, I think he/she means lifts in a VEX competition, not in the real world (correct me if I’m wrong).

7

OK. I would agree with this for competition heights. I would also note, though, that where a lot of the prior discussion came up the OP also didn’t restrict the list to competition lifts.

8

Please go on. :smiley: So far, we know for now that RD4B are fast and efficient but not so space friendly and you’re only lifting on single cone that doesn’t even weigh more than .3 lbs. Maybe there’s has to be another way to lift such a small load at a high altitude… So much mechanism for a single cone.

9

Yes, see the LOL (List of Lifts)