Vertical Chain Lift

Majority of vertical chain lift mechanism follow the 1103 style, that is to say, 2 sets of linear slides per stage. however, i feel that these linear slides are too close to each other ( 5-holes apart ). thus i am thinking of having one which is about 18-holes or 20-holes apart. technically speaking, it should be more stable than the 5-hole apart ones as the 5-holes apart can turn left and right when suddenly stopping after turning. am i right? please correct me.

Actually, (if I am understanding your question correctly,) having the Linear Slides farther apart would cause you more problems. The slides being far away from each other can allow more bending, as they are stretched to a far extent, causing the slides to have a lot of friction, as they still needing to move in sync. It would be best, theoretically, to use a single Linear Slide. However, this allows a lot of twisting when turning, for instance, as you said. To fix this most robots have two, but I believe (if you build it structurally sound enough) you should be fine with ~5 holes apart, and I think that is plenty good spacing to prevent twisting. Look at 1103’s robot, as you mentioned. He uses 5 holes apart and yet I don’t see any problems at all with his vertical lift twisting, and he had a semi-fast robot, which was turning quite quickly.

Just my opinions, someone else may come back and prove me wrong, but I’m pretty sure my hypothesis is correct.

~Jordan

that is true. but my school has a special way of making linear slides slide properly vertically with very little problem. by loosening every screw that connects every linear slide to a metal structure. tighten one of them, and test. repeat the process until all screws are tightened. at most, i could use locking screws and they would never loosen. wouldn’t they remain and not bend/loosen to cause more friction?

The rotational torque on the linear sliders that occurs after turning can be countered by finding linear slides that fit really well, securing the slides strongly to the rest of your mechanism, and tightening the sliders so they don’t wiggle (like you said your does).
Generally, the slides slide well enough with a little lubrication and you don’t need to worry about any severe wobble. Spacing the slides further apart (at ~20 instead of 5 holes) will probably not make a significant difference, as there is quite insignificant rotational wobble even when the slides are 5 holes apart and mounted correctly.
The reasons I would mount the slides closer together are: 1) More compact system; 2) Relative movement is limited due to short support pieces connecting the slides; and 3) More jam resistance (when the slides are tilted to the side, there is more displacement with slides that are further apart).

ok. now, i hav a working vertical chain lift which worksrather well. 6 269 motors, powering a vertical speed of about 21 ( 30 being the largest sprocket driven directly and 6 being the smallest sprocket driven directly ) and a not so weak strength. however, my linear slides are not lubricated/smooth and reaches to ~35" in 4.9 seconds ( iphone timer ). which means, i can power a 24-teeth sprocket with 6 motors at 1:1 ratio with a little help of lubrication and elastic. what i am worried is whether its strong enough.
3008a have a similar lift of speed 18 and the strength of about 5.2 motors.
1103 had speed 16 and 6 motors, but he needed to carry his whole robot.

What unit are you using for the “speed” of your lift? When making a vertical chain lift in which the chain is fixed to the linear slides, the only determining factor in its vertical speed is the first sprocket and anything between it and the motors. The 6t sprockets that the chain moves over should not affect the speed because the axles are free to spin.

6 motors on a 24t sprocket gives you ~50in-lbs of stall torque, so at 1.5" (the radius of the 24t sprocket) you will have 50in-lbs*1/(1.5)in=~33lbs, so you’re running optimally with about 15lbs of force, which is a lot…
The reason 1103’s was so slow was because it had elastics pulling the list down to assist in hanging. I think you should be able to get at least twice as fast as 1103 with 6 motors considering you don’t need to lift a robot and you can actually use the elastics to help your motors.

6 motors, 60-teeth gear each, driving one 84-teeth gear which is connected to a 30-teeth sprocket. ( very huge “supermotor” concept gearbox ) from what u said, its possible for 6 motors to drive a 30-teeth sprocket with a 1:1 gear ratio? thats fast.

It’s physics people.

Think about it. It’s the same principle that ice-skaters use. If everything is close together, it can spin fast, but if you spread it out, you slow down.

Moment of Intertia:
I = 1/2 ω^2 m r^2

m is mass as usual.
ω is angular velocity in radians per second. (good units when you aren’t being specific… Like with a robot spinning)
r is the distance from the axis of rotation.

I know it’s difficult to figure out what the specific weight is, the specific distances and all that, so I would recommend an integral for anybody who wants to really do the math.

Anyways, with the equation, you can see that as you get further from the axis, your inertia will expand exponentially. So my recommendation is that unless you really want to over-design your system, stick with the 5-hole C-channel…

Try it and see. I would first set up your lift with all of the elastics set up, then run it by hand and get any frictiony spots taken care of. Once that’s done, 6 motors if more than enough power to raise the lift. I’m considering just using 4 269s on our lift.
1103 had enough force downwards to hang the robot (~18lbs). Assuming your intake with all of the objects loaded into it is 5 lbs max and you have elastics pulling it up, you should be able to go even faster than 1:1. I know I didn’t take into account the weight of 1103’s intake, but it was probably less than 5lbs and the main force on the lift I was concerned with was the hanging part.

We’re talking about a vertical lift here, so the only moments of inertia we’re dealing with are of the gears and sprockets (no arms I think).
But good stuff :slight_smile:

Oh, sorry… I was referring to the questions beforehand, about stability… Regarding lifts being spread out, or compacted to a small area…

I have built three of these lifts at 5 holes wide and put an intake on suitable for gateway and I find that 5 holes wide is stable enough and it is a lot lighter then larger ones

now, i have a working lift of speed 30 ( 1:1 on largest sprocket ) using 6 269 motors with the help of a little elastic. its rather fast . but there is no mechanism on it. it even goes down slower than it goes up.
this is only achieved today after lubricating the slides and having the elastic helping the lift up. thanks people for ensuring that i can have a faster-than-what-i-thought-it-can vertical chain lift.

Nice :slight_smile:
We just built a double-extending elevator today to prototype, and it works with surprisingly little friction already.

in one day? thats fast. and i realised to day that my lift was powered only by 5 motors, one wasnt working at all. so i changed, and it works fine now. apparently, the elastic snapped. twice. gotta work on that

Well we had an hour and wanted to make a prototype. It is quite ugly and doesn’t run too well (chain is hitting stuff, no stops, etc.), but it demonstrates the idea well enough.

Are you using rubber bands? The challenging part of using elastics on a vertical lift is that the elastics go from being stretched all the way to not being stretched at all, so the force is not very constant.

i know a counter weight would have a constant force helping the lift up, but mine doesn’t seem to have enough space for heavy and compact objects
and because of the above, i feel like giving up on it

Think about the physics of springs vs energy, and you may be able to come up with a plan for elastics or Vex latex tubing that will give more constant force.

Gravitational PE (Potential Energy) in the dead weight of each section of lift is MGH.
The last section has the smallest mass,
the next to last section has mass of last section plus its own
the next to that moving section …

The PE in a spring is 1/2kxx (hooke’s law)

The difficulty is that the PE needed is linear with linear slide displacement H, but the spring energy is squared with displacement x, using H = x doesn’t fit very well.

One way I’ve mentioned in the past to align these two is to use a cam.
You already have (or can add) an axle whos rotation is linear with H.
It may work to gear this up to another axle that runs slower, put an offcenter sprocket (acting like a cam) on this axle, with a chain ending in elastic spring.
Its a little complicated, but if you can design it with a spreadsheet and document it in your engineering Notebook, it would look really good for Notebook based awards. Plus its “real engineering”

https://vexforum.com/showpost.php?p=214438&postcount=19

This would be a relatively easy way to use elastics without going outside of your basic lift shape (the narrow verticle column).

I would not recommend a counter weight just because you can use elastics to do the same thing.