Scissor Lifter?

[waialua359]

Originally Posted by asid61

Why and how? This seems to be a very contradictory veiwpoint here, and I'd like to hear your thoughts. What is your experience?

We built one in 2003 stack attack and it stacked bins very nicely. The scissors lift only had to go 2 bins high max.

[sviridovt]

Let me just repeat every one here: NO SCISSOR LIFTS unless you want to know what hell feels like. The only time one should even consider a scissor lift is when you have to lift for small distances, with only one layer. Anything more will be waaaaay unstable.

[waialua359]

Originally Posted by sviridovt

Let me just repeat every one here: NO SCISSOR LIFTS unless you want to know what hell feels like. The only time one should even consider a scissor lift is when you have to lift for small distances, with only one layer. Anything more will be waaaaay unstable.

While our team probably won't be making one, I'd bet that it's still possible to create an effective one for specific purposes.
How ironic that the best VEX robots this year all use scissor lifts, where the game requires precision and going really high.

[InFlight]

A scissor lift to raise totes is probably an overly complex and likely too slow in operation compared to the alternatives.

Ideally you should want to raise the totes in an about a second or two at most.

[Matt C]

If you look at my avatar, we built one during my high school team's rookie year (1999, team 311). Took us 4-5 weeks and 2-3x the allotted weight to get it working properly. I tend to steer students away from the scissor lift, though I don't like to outright eliminate it as a possibility.

The 1999 application was before pneumatics and I think using pneumatics would make it to develop the scissor lift, but I still don't think it's worth the weight, size and complexity when other options are available.

Originally Posted by IndySam

#1 No casters.

One note; team 311 went to the rubber match as the alliance captain in the finals on Einstein in 2002 with casters.

[TheCrayButton]

Our team had great success with a scissor lift in 2012. We actually won a regional with it. Here is a video of it. http://youtu.be/jFwkC_s2BAQ?t=53s

[JCharlton]

Originally Posted by ShinyShips

There are only two rules when designing on our team:

1. No turntables
2. No scissorlifts

Ours are:

1. No Tank Treads
2. No Scissorlifts

We did both in our first year and haven't done either since.

[EricH]

No experience, except that I spend a lot of time on man-rated industrial scissor lifts.

If stability is important, scissor lifts of more than one stage should be rated as do not use. I walk from one end of a lift to the other, it sways a bit.

If simplicity is important, scissor lifts in general should be rated as do not use. (See: elevator system, pneumatic lift)

If you can't do much precision work... See the bold text above.

If you are seriously considering doing a scissor lift system, you should do the math. I've heard of engineers getting scared of that math. You need to account for all the stages, the stability, and the precision needed. It's not easy.

[Nemo]

Two more things that make scissor lifts hard:

1) One or both of the bottom sections has to slide across the bottom surface as it extends upward. Getting that to work smoothly with low friction and without wobbling around is tricky.

2) Powering a scissor lift without hydraulics is hard if you're lifting a decent amount of weight. When it's fully retracted, you have to supply a lot of force to get it started, because the initial angle is unfavorable. Certainly it can be done with motors, but I think it's a lot trickier than powering an elevator or an arm.

[asid61]

Originally Posted by Nemo

Two more things that make scissor lifts hard:

1) One or both of the bottom sections has to slide across the bottom surface as it extends upward. Getting that to work smoothly with low friction and without wobbling around is tricky.

2) Powering a scissor lift without hydraulics is hard if you're lifting a decent amount of weight. When it's fully retracted, you have to supply a lot of force to get it started, because the initial angle is unfavorable. Certainly it can be done with motors, but I think it's a lot trickier than powering an elevator or an arm.

Thank you! We'll keep these in mind if we prototype one.

[pmangels17]

In our initial prototyping, we drew a number of designs on a big whiteboard for lifting the totes, including a scissor design. That image was quickly circled with red marker multiple times, and then in bold and exclaimed letters indicated as "Do Not Use!!!" I cannot tell anything else about our design (because we are still finalizing stuff) other than we will most certainly not be using a scissor lift because its incredible complexity and inconsistency. There are many more successful designs available, if you are stumped I suggest you start by looking at the various RI3D elevators and arms, they might serve you better.