Hi, i m from team 1241C, theory 6 robotics, and i was wondering how a double stage linear slide works without using chains. i have seen a lot of teams do it and just couldnt figure it out. If anyone can explain how it worked, or post a pic or vid that would be great!
Thanks
Check out this thread: https://vexforum.com/t/team-1103-robot/18347/1
It’s long, I know, but if you really want to learn, you’ll dig for it… 
I’ll warn you: it’s a little hard to get “smooth” - the slides like to stick/jump, especially if what you’re lifting is heavy.
You could use string given you have enough to do that through pulleys and such. use the winch kit and you can make one pretty easily. It would work just like the chain but only with string and pulleys instead of chain and sprocket.
True, but then you lose the ability to “power down” - it won’t have the motor’s force while lowering. In Gateway, this isn’t so much of a problem, but it was (slightly) in Round Up.
check this thread for some pictures of my team’s bot from this year. You can see we simply powered each set of slides with two motors. We used small gears on the back to hold the weight and larger gears in the front to get extra speed. There can be some friction that needs to be eliminated, but overall the slides worked great. Just make sure you don’t put too much weight on them. Hope this helps!
https://vexforum.com/t/team-1200e-bot/18769/1
You can use string to power it down, just use a second pulley that’s geared to the first with string running up the length of the lift.
To do a double-extending lift without chain, using string would be easiest, but I think what you’re asking is about how to use racks and pinions. In that case, you just need to set up the rack and pinion mechanism like you would with one set of slides, but add another set on top of it.
There are lots of explanations in this forum about how to do this, just search 
THANKS!! exactly what i was looking for! i just have one question, i have seen that in these types of lifts, the 1 set of slides go up first then when they reach the top, the second set starts to go to the top. How does it know to switch to the second set of slides once the first set reaches the top? is it controlled through programming? or are there some kind of mechanics involved?
If you use string both lifts would probably go up at the same time depending on the way you did it. It would be a mechanical thing in anyway I would do it.
i m not using string. i m talking about how u would do it in rack and pinion.
Why would you want that? Your lift would be faster if both extend at the same time. I have a feeling that you were looking at chain-based double staged lifts and thought it was done with rack/pinion.
If you do want that motion, then you could use limit switches or encoders to determine when each stage is extended completely.
Yeah, i was watching some videos and saw some robots whose lifts went up at the same time, how are they doing this? is it controlled with programming? or mechanically?
You could also have 2 rack and pinions back to back. With the inner forward rack being attached to the top of the backwards outer rack. You have the gear thats driving the forward rack be at the top. And the gear thats driving the backwards rack at the bottom. then chain them together. so they both move at the same time. but from one set of motors. Its confusing I know, but can be worthwhile.
Ok, with our lift, each set of slides was controled individually. This doesn’t mean that you can’t raise them at once, just that you have more control over them. It’s much faster raising them at once, but if you do need them to move individually (one making it to the top, then the other extending) you could use bumper switches. Place a switch so that it is pressed when one set of slides is extended, then program it to start the other motors when this is pressed. The easiest way is to simply program them to run on different buttons, or run all the motors on one button. Its up to you. Any more questions? GOOD LUCK!
This is the easiest way to power both at once, as it consolidates your motors because they’re all mounted to the same slider, so there are less bulky parts moving relative to each other, and the parts are moving slower.
Yeah, i asked a couple of our mentors, and they said the same thing. THANKS FOR ALL THE HELP, i m gona test each scenario and see what works out best 