I am currently making a robot that uses scissor lifts. It seems like there are few ways to make a scissor lift so can anyone tell me the most efficient way to make a scissor lift? Thanks!
It depends a lot on the scissor lift. The biggest issue a scissor lift faces is instability caused because the 2 halves of the lift can move independently of one another. To solve this issue, cross bracing, a relatively narrow lift, and independent PID on each side of the lift can ensure the entire lift moves rather than just 1 side. A few other innovations are possible as well:
While there is no one most efficient way to construct a scissor lift, using screw joints, reducing friction in each joint, reducing the number of joints, and using rubber bands to cancel the weight of the lift all increase the efficiency of the lift. It's also possible to increase the speed by adding motors or increasing the gear ratio.
Scissor lifts are very tricky to built correctly, but a few outstanding scissor lifts have been made in vex before, and they can get quite close to the speed of a DR4B. Good luck!
Just look at the real world, you'll see plenty of examples of scissor lifts in use. They are good for certain purposes. Sure, in VRC they tend not to be preferred. However, I see nothing in the OP saying VRC. Maybe this is a learning thing, maybe it's for a totally different purpose than VRC, maybe it's something else... Just saying things like "don't" when we're not even given context isn't helpful with regard to the OP.
Unfortunately, I haven't played around with scissor lifts enough to give much good advice at this point. From what I've seen of VEX scissor lifts, you'll want to pay a lot of attention to stability. They seem to twist a lot, so you'll want to put a lot of effort into keeping things lined up well and keeping the joints from being too rocky while letting them slip without too much friction. As for locating the bottom of it, I would tend to prefer locking one bottom corner in place; I don't think trying to slide both is good - you need more stability. As for motor location, I would mount motors at the bottom, not at an X. That's certainly not the best for all situations, but why raise the motors if you don't have to put that extra strain on the motors. As for rubber bands, I would tend to place them horizontally between the pivots at the ends of bars. But those are mostly under-informed, general opinions not specific to whatever purpose you want.
@Alumination Robotics Yeah just look at pretty much any Skyrise video and tell anyone that scissor lifts are good.
So like this video which shows that 33% of the World Finalists that year used Scissor Lifts. Or this one which showcases an undefeated number one division seed that used a scissor lift? Sorry I just hate how this year bashing of a perfectly good linear lift system has happened because "everyone" used a rd4b in 2015. As far this year goes this video has about the highest scoring teams I think I've seen so far.
As far as building a scissor lift goes, friction and stability are the major items to overcome. Here are a few things our team is trying to help fight those items. Using nylon nuts with screws at the joints to help reduce friction. Using two linear rails at the bottom of each side to help with stability and travel. It's not a fast build to get right, but honestly no linear lift is. Another "standard" if you will is the lift should barely stay down with the rubber bands, and if you lightly press up on the top of it with your finger and no motors attached it should go up without any help.
I don't have much advice to give, but I can tell you this: unless you have had more than a bit of experience in robotics, your first build will inevitably look like this. Scissor lifts are not easy to build; you will need to keep working on it and improving it.
I think scissors lifts, done well, are a great solution this year. My word of warning is this...
...the lift should barely stay down with the rubber bands, and if you lightly press up on the top of it with your finger and no motors attached it should go up without any help.
Be very careful about the height of the robot when it gets to this point. Several years ago I witnessed a robot that would be "mashed" down to pass inspection. This would get some of the arms locked to each other. On the field the drive team would "fluff" the robot to make sure everything move freely, but the opposing teams called for sizing check and the robot was more than 18". They would then have to mash the robot down to start the match and their scissor lift would not work nearly as well.