Currently there’s a lot of talk about the various lift systems in vex. However I have noticed that there isn’t a detailed list anywhere on this forum. Therefore, why don’t we start posting about every type of vex lift there is or has been.
Some guidelines and tips:
DON’T REPOST IDEAS (if someone has already mentioned a type of lift here, don’t say it again, this is to avoid filler)
DON’T REDIRECT TO ANOTHER DISCUSSION (just copy and paste the information, it will save time scrolling through posts)
ADD MISSING INFORMATION (if someone left something out about a lift, quote them and and the info)
SPECS AND DETAILS ARE KING (just saying the name of a lift isn’t helpful. Talk about the range, motor count, power, etc)
Scissor Lift!
Reasons to use:
It’s both slow AND unreliable!
It’ll probably require more motors than any other lift!
It takes more upkeep than any other lift!
It weighs 2* more than any other lift!
Is hard to band!
It bends metal like crazy!
Questions like that can’t truly be answered without designing a full robot, a scissor lift could have any range of motors on it and depending on how you build it it could be lighter or heavier than others affecting how long it would take to fully raise. For example you could build a 1 motor scissor lift with an extremely high gear ratio or a 12 motor scissor lift with an extreemely low gear ratio.
Linear slides:
Pros:
-Stable
-Reliable
-Vertical lift (manipulator will not move back and forth)
Cons:
-Slow
-Limited to ~20 in. In height before friction makes it REALLY slow
Reverse Double n bar, AKA rd4b, rd6b, rd8b, rd46b, rd48b, etc. These bar stack a four bar, six bar, or eight bar on another one, reversed, so that they will lift linearly
Pros:
Can reach very tall
Can be very stable
Can be very fast
linearly lift
Cons:
Somewhat harder to build
If built incorrectly, can be very unstable and slow
I would think another limitation of reverse 4-bars is that your robot cannot reach out to score. The straight-up-and-down behavior can be both a strength and a weakness.
I’d be curious to hear what facts back up these statements. The reason I’ve generally seen people’s linear elevators are slow is because they just did not make an effort to gear the mechanism correctly. Also not sure how you came up with the 20in figure. A standard linear elevator when done correctly can get probably 25" of lift with only 2 stages. And adding a third stage does not hit the threshold for diminishing returns like your statement suggests.
I feared someone would bring up my 20" figure, I completely forgot how long the base slides are, my bad.
As for the “slow” figure, that is in comparison to the, as far as I know, indisputably faster DR4B, or 2 bar (though maybe not a scissor lift). To attain these speeds, as far as my experience dictates, the motors on the liftv would have to be externally geared up.
Linkage lifts tend to be externally geared down in most VRC applications, so not sure why there is a downside of having to gear up linear elevators when comparing systems…
When done correctly all of the different lift options can be effective. In the end which one is best generally ends up being which is able to be the lightest, most stable, and most efficient system which will depend on the application for the most part. Arguments could be made that scissor lifts would not be included in this, at least for most competitive robotics applications.
I will disagree that scissor is totally not suitable for robotics games.
There are many great examples of teams using scissors and did very well.
Some that came into my mind - many of the Chinese teams and also 8066 teams built some real mean scissors lift.
And how abt 7682 scissor lift for skyrise?
All these are great examples.
Granted it is technically challenging to build a good scissor lift (especially when it is more than 2 tiers), but if built right, they can be very effective for linear motion.
Scissor lifts have some advantages, which is why they are used so much in the real world. For example, all your motors can be at the bottom with even a very tall lift. This matters a lot more with gasoline than with electric motors in VEX, but it could still save you from needing many extension cords. Also, the need for the joints to move away from each other makes it really easy to lock scissor lifts in place for safety.
Let’s say you want to build a lift that rises 10’ (just over 3 m) straight up while maintaining its orientation out of VEX parts but is small when collapsed. What method would you use?
I’m not saying it’s the best type of lift in general, and especially not for VEX competition. But if it were truly never the best type of lift for any purpose, I doubt we would see so many of them used in the real world.
