Scissor Lifter?
 

Hey all, I was just wondering about experiences that other teams have had regarding scissor lifts??

All comments welcome, I'm just trying to explore all of the possibilities!!

Re: Scissor Lifter?
 

Put it this way, I doubt anyone has ever built a Second scissor lift:)
Seriously though they rarely work very well, they all seem to wobble a lot when they get very high.

Re: Scissor Lifter?
 

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.

Re: Scissor Lifter?
 

Very well put. Scissor lifts are just way more complex than they need to be for FRC application. Most of the Ri3D teams chose to use elevators for a reason. They are simple, can be light weight, and effective.

Re: Scissor Lifter?
 

No. Absolutely not. But I am sure we will see a few teams using them.

Re: Scissor Lifter?
 

We used a scissor lift once on 842 back in Ultimate Ascent. We used it to bring Frisbee to our shooting mechanism because we somehow forgot about gravity. I don't think you could pay us enough to make another scissor lift. Despite it being very small and simple, it was very inconsistent, never landed right, jammed regularly and overall wasted dozens of hours due to having to adjust it. Even if you can get one working quickly compared to an elevator, the time spent fixing and adjusting it is not worth it at all.

Re: Scissor Lifter?
 

At the start of each season, I remind the team of our two absolute rules (born from very bad experiences):

1. No mecanums (yes, even this year)
2. No scissor lifts

My FTC team came to me with a design that included a scissor lift. I asked if that was the best design the could come up with. They said it was. I said you need to try harder! The have a much better design now!

Re: Scissor Lifter?
 

There are only two rules when designing on our team:

1. No turntables
2. No scissorlifts

I haven't had any experience with scissorlifts, but our mentors must have a really good reason for not wanting to ever have one.

Re: Scissor Lifter?
 

The Digital Goats have two rules.

#1 No casters.
#2 No scissor lifts.

Re: Scissor Lifter?
 

I have one rule that applies to FTC more than FRC and it is as follows:

Unless you have to raise an object more than 20ft in the air. A scissor lift is not the answer.

(Bascially unless we play a game like 2011 (bowled over) again you shouldn't need to use a scissor lift.)

Re: Scissor Lifter?
 

Bowled Over was 2011-12. I'll agree that it was probably the only time I've ever seen a scissor lift that was actually effective. Seeing teams shoot those crate 20-30 feet up with elastic powered scissor lifts was both really cool and really scary.

If you want to be successful this year at competitions, a scissor lift is almost certainly not the way to go. Build a nice elevator or something. You only actually need one stage this year.

Re: Scissor Lifter?
 

Out of curiostity, what's if it's single stage? I.E. Two bars that cross with a joint in the middle.
Assume that it's milled accurately and not made on a drill press.

Re: Scissor Lifter?
 

We used a scissor lift in 2013 to score the colored discs while our robot was on the pyramid. We needed a compact mechanism to lift a few frisbees a few feet, and I thought it worked great for us.

Obviously this is very different than lifting totes;however, I think they can work well in specific applications, and to automatically rule them out is a mistake.

Re: Scissor Lifter?
 

Ours are:

1. No Tank Treads
2. No Scissorlifts

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

Re: Scissor Lifter?
 

I understand why casters and agree.
but whyscisser lifts

Re: Scissor Lifter?
 

Nothing wrong with scissor lifts!:)

Re: Scissor Lifter?
 

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

Re: Scissor Lifter?
 

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

Re: Scissor Lifter?
 

We built one in our rookie year (1996), we never even thought to replicate that experience since. I use a scissor type man lift here at work on a regular basis. In order for it to work well, a rigid precision frame and bearings in the joints are essential. The problem with most is the non-precision with which they are built. This leads to instability while moving and therefore intermittent loads that exceed the ability of the drive to overcome.
We have a do not use list too...
No casters/shopping cart wheels for obvious reasons.
No omni wheels on ramps.
Anything else that does not fit the game.

Re: Scissor Lifter?
 

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.

Re: Scissor Lifter?
 

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.

Re: Scissor Lifter?
 

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

Re: Scissor Lifter?
 

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.

Re: Scissor Lifter?
 

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.


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

Re: Scissor Lifter?
 

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

Re: Scissor Lifter?
 

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.

Re: Scissor Lifter?
 

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.

Re: Scissor Lifter?
 

I remember doing a scissor lift and once you get all the kinks worked out its fine, but the amount of moving parts makes it more likely that things will go wrong the taller you get with it. There is a niche that scissor lifts fill and if this niche needs to be filled go for it.

Re: Scissor Lifter?
 

I am quite frustrated by the "we'll never do X because we tried it once and it didn't work" attitude. I find it very narrow-minded and a bad precedent for our students. Technology, collective experience, and requirements all change, and we should be willing to reconsider past decisions and be able to admit to ourselves that we could have done something better.

95's name-sake robot, Grace Hopper, used a scissor lift with great success. The compact storage profile of the lift allowed the robot to be completely mobile on the field and still reliably, and quickly, score in the high goals. Also, Grace's scissor lift was fabricated with a lathe, drill press, and belt sander. Precision machining equipment is not required.



Here is an old match video to show what the field was like: https://www.youtube.com/watch?v=YCcBXMrR8DY

Scissor lifts have a very specific application: they allow a mechanism to reach very far while being stored in a very small space. With the lack of height-restricting obstacles and lack of size constraints this year I don't think a scissor lift is appropriate. But I would consider it in the future.