Just wanted to talk about elevator lifts. Specifically how to power them and what gear ratios to use. I have already built mine and am satisfied, but id like to see how the rest of the vex community is powering theirs.
My team’s lift is a 5 stage, 6 motor loft geared 2:1 with high speed motors. It is very fast. It can only support 1 cube at a time and of course a skyrise piece. It goes to 70 inches. However, our lift is not very strong. While it can support 1 measly cube, it can not lift the cube to max height. The cube goes up around ~60" because the torque requirement is too high as the lift goes to raise the final stage.
I really like the chain driven elevator lifts, but I don’t have any chain. I can’t seem to understand how multi-stage linear motion elevators work, or just the timing of the different stages going up 
Our team has a 3 stage lift with six torque motors. We use the 18-tooth sprockets to power it. We can lift 3 cubes to the middle post and can reach the 4th skyrise, but can build 5. We are going to add another stage in the future.
I think if people are going to describe their lifts and what ratios they’re using, etc. then you need to include if it is a continuous or cascade system. That changes how quickly/how much force is needed to lift up.
I’m guessing your elevator is continuous? If it is getting harder to continue lifting towards the end that sounds like continuous to me. With continuous, you extend one stage at a time, so the higher you go, the more stages you’re holding up in the air. So that last ~10" is about the extension you have left from your last stage. That last bit of weight is probably proving to be too great for your motors to overcome. To fix this you would need to add a motor or two, or slow down your ratio.
I’m not going to post a lengthy explanation of elevators and the various ways to set the system up, as I know there are other threads that have gone over this before. Try searching for “elevator”, “cascade”, and “continuous” and see what you find. PM me if you’re still wondering about things or have questions.
I’ll just leave this basic diagram that shows how a continuos and cascade elevator are rigged. Keep in mind that with cascade, all of the stages extend simultaneously at the same rate, so it moves faster than a continuous elevator, but requires more force.
What continuous vs. cascade really does is change your drive ratio for the elevator. The more stages, the faster a cascade will travel vs. a continuous. For example, If I have 3 moving stages on both kinds, If I pull my chain on the system (or cable, etc.) 12in to make the systems extend, the continuous will extend 12in while the cascade will extend 36". If they were 4 stages, the continuous would still only extend 12", while the cascade would now extend 48".
Please PM or reply here if you have more questions.
-Nick
We built a three stage lift with string and pulleys and a four motor powered wench with four 64 tooth High Strength gears.
We had a 4 stage cascading elevator powered by both string and chain. We used 6 torque 393 motors on a 1:3 gear ratio and could get up to 2 cubes to max height (almost 60 inches) in about 7-8 seconds.
Yeah sorry, my lift is indeed a continuous lift design. Also, there is no way we can add more motors, there are already 6 put toward it. However, we could change our motors to high torque.
One of the teams I mentor uses a 6 stage continuous lift with a 1:1 ratio with a 2:1 torque mechanical advantage (half-inch winch). Reaches the top of the skyrise in about 8 seconds with a cube and skyrise but it did begin to burn out near the end of competition.
Yup, exactly that. I totally forgot the link when I finished typing, my mistake.
If you cannot add more motor power to it, then you need to re-evaluate your gear ratio. Changing the internal gears on the motor (High Strength, High Speed, Turbo) is included when looking at your gear ratio. I would definitely suggest starting by changing the internal gears to high torque, as that would not require you to take apart and re-do the whole system. It’s also the smallest speed reduction you can do (without getting very complicated with multiple stages of external gearing).
If changing your motors to high torque still isnt enough, then change your system to a 1:1 ratio after the motors and try running it that way with your motors back at High Speed.
If it’s still no good then last ditch effort keep the system at 1:1 after the motors annd switch the motors to high torque. If it still has issues then your ratio/motor power isn’t the issue.
Just to keep things straight-forward:
Turbo Internal Gears (240rpm output) x 2:1 system ratio = 480rpm
High Speed Internal Gears (160rpm output) x 2:1 system ratio = 320 rpm output
Turbo Internal Gears (240rpm output) x 1:1 system ratio = 240rpm
High Torque Internal Gears (100rpm output) x 2:1 system ratio = 200rpm output
High Speed Internal Gears (160rpm output) x 1:1 system ratio = 160rpm output
High Torque Internal Gears (100rpm output) x 1:1 system ratio = 100rpm output
You can figure out your linear speed output based off of that along with knowing the diameter of t=your drive sprocket.
I would suggest doing some trial and error and finding which setup listed above works best. It’s all about finding that happy medium. This is a great example of how designing ahead of time can really save time in the long run. Running some numbers can tell you quickly what ballpark you should be in to use for a ratio.
Another thing that could help would be to find places you could reduce weight without affecting the performance. However, I highly caution you to not sacrifice your desired cube capacity to fit your strategy just so the elevator works. Make the elevator work for your strategy. You will find more success in your season.
Hope that helped some.
-Nick
What would happen if you had a cascade lift with seprate motors powering each stage? As in two motors on the tower, one on the first stage, one on the second stage one on third stage ect. Would that help, or would three motors on the tower, two on the first stage, one on the second stage? Is anyone feeling me?
I’ve never tried it, but it would probably reduce the backlash similar to powering different stages of a scissor lift with orbital gearing or with the rd4b. However, its probably not worth the extra weight and vulnerability since cascades don’t have much backlash compared to either of those systems.