For this season’s game, my team is looking into the possibility of using a scissors lift powered from the center (the so called Chinese scissors)
We noticed that most, if not all, of the scissors lifts we found had the motors mounted on the lower most tier of the lift.
We were wondering if the tier in which the motors were mounted on made a difference since no one seemed to power it from the top most tier. Which would be the best to mount the motors on? (or it doesn’t matter?)
Talking about lift performance, theoretically it doesn’t significantly matter.
However, there are factors to consider. For example, by mounting motors higher, they will take up central space when the lift is compressed, thus there are more limitations for your intake design. Remember if you do put motors higher, you will lift the whole gear and power system higher every time you use the lift, wasting extra energy.
Just a few things that came to my mind.
Plus: i am doing a same lift also!
However, let’s say we have a 5 tier scissors (that’s overkill xD) would mounting it on the center tier be best? Since there is a lot of slack between tiers on a scissors. By having the motors on the center of the lift, there would only be two tiers of slack (top and bottom) as compared to four tiers of slack If it were o be mounted on the extreme tiers.
I see your point. At this point I have only experimented with one powered at the lowest tier, so I cannot give you the definite answer. Situations vary and you can possibly be correct.
By the way, I don’t think that five stage scissor is overkill. Say that you use 17.5 inch bar for structure, which means longest bar possible in high school vex. You make a four stage lift and raise very high, and each stage is 16 inch high. So accounting the height of the base, your top of the lift reaches about 67 or 68 inches or so. You want the point at which you intake your cube to rise above 60 inches and score on a full skyrise. Therefore, you may need a slightly higher lift to score cubes on a full skyrise.
Prepare to overkill your lift… you need 5 tiers to get to 60 inches this year
edit: nvm, cca beat me to it
Yeah we built it a 4 tiers and it would work if you use the intake to pick up and exit out the back so the intake makes up the extra tier. 5 is the only way to get that high.
It’s not overkill if it’s serving your team’s design purposes well. We’re doing a 5 stage scissor and we need all the height we can get.
how did you manage to counter the slack with 4 tiers? my team made one but scrapped it as it was too unstable and had problems lifting due to the enormous forces needed to start.
I have experimented with scissor lifts and the Danny lift and found that the best place to put a motor to counter for the slack of the lift is the top of the lift. This way, the lift only has to overcome one section worth of slack each time, instead of all at once. The downsides to this is that it is harder to fit an intake in with a motor at the top, and you have to lift the weight of the motor farther.
There are lots of issues that affect the overall performance. Is your slide lubricated? Did you directly put screws or shafts into square holes without bearings to make joints? Is your gearing secured and reliable?
In our prototype we used screws and nylon nuts as joints, and we used bearing flats for each single joint. We secured each single bearing flat pretty well because we designed enough spacing. And so far, slack is not that drastic of an issue for us. Maybe trying to design a more reliable system is your improvement space.
Plus, ever tried rubber bands? Unlimited free energy!
We are using only three stages on our scissor lift, and we will still be able to reach ~68". It sounds impossible, but it actually works; I CADed the whole robot already and made a prototype lift IRL, and it does actually reach the five feet and then some. We may add a fourth stage anyways, to maybe add some more stability and speed up our lift, but it is possible to do it in three.
Are you using 17.5" pieces of VEX metal? Even if you could extend the scissor lift so that each of the three stages had vertical components (e.g. stacking three 17.5" pieces on top of each other) that only will measure 52.5 inches above the mounting point. What you are saying is impossible, unless: 1) your definition of “stage” is different than ours, 2) you aren’t using only a scissor lift, or 3) you are mounting your scissor lift > 15 inches above the ground.
Assuming the third option (because I think it’s most likely), you still only have a range of motion of < 52.5 inches–that is, unless your intake has some other way of lifting cubes, you can’t get a cube above 52.5 inches, even though the top of your robot is 68 inches in the air.
Hmmm… what seems odd about this. There is a maximum, it is not unlimited. You are limited to the number of rubber bands in the world. And buying all the rubber bands in the world doesn’t seem free.
Our robot is a little unusual, which is part of the reason that this works; the reason we make it to ~68" is because, while we only have a range of motion of about 46 inches, in our starting position, our intake intakes from below ground level but outtakes at the top of the robot. It shifts slightly upwards once the match starts through the magic of rubber bands, so as to intake at the proper height without moving the scissor. It also expands a little bit at the top in order to cram in an extra cube, which is where it gets a few extra inches to make it all the way up to the top of the pole. Our Skyrise manipulator is going to be a little strange, too, so as to allow for the smaller range of motion; however, it should actually be as accurate and possibly faster than a regular claw 
Basically, if you get creative with your intake design, you can do some interesting things.
Tank Thread? The thing about that is that it is slow to intake and score.
If you use the sprockets the tank kit comes with, sure; but the 60T HS chain sprockets are 4x as fast as those sprockets, and we will be gearing our motors internally for speed as well. We should be able to score 5 cubes in just over a second, and pick them up almost as fast as a “magic intake” with side rollers.