Scissort Lift vs. Crane vs. 4-Bar Lift vs. Gas Springs

[Hiteak]

I would not recommend doing a scissor lift. We did that for last year and it was really slow.

[dtengineering]

Not all scissors lifts need be slow. Team 639 built a scissors lift that could extend to grab "the bar" in about one second back in 2004. http://www.team639.org/index.php?page=r2004

What was more impressive was that it did this from a fully collapsed state. Anyone from 639 care to give some specs on how you did it?

Jason

[sethw]

Originally Posted by dtengineering

Not all scissors lifts need be slow. Team 639 built a scissors lift that could extend to grab "the bar" in about one second back in 2004. http://www.team639.org/index.php?page=r2004

What was more impressive was that it did this from a fully collapsed state. Anyone from 639 care to give some specs on how you did it?

Jason

We were able to build a very fast pneumatic scissor lift in 2004 using two 1.5" bore pistons. I'm not sure of the exact stroke length, but I know it was somewhere around 10". The lift itself was made of 1" square tubing members with occasional cross braces. However, the system we created was not very sturdy, and was meant to be used more than once in a match. Ideally, it would never be dropped back to its retracted position using the pneumatics - doing so sent it crashing down extremely quickly. It would be possible to prevent this, but the entire assembly was fairly fragile, and we ended up bending and having to replace nearly every part of the lift at least once over the course of two regionals. That was without lifting a load. Also, the pistons we used had to be very large to give us enough force, meaning it drained our air tanks to about half pressure every time we used the lift. Granted we are able to use twice as many tanks this year, but it is still a significant amount of air for a single lift. With modification, it may well be possible to create a similar system able to be used repeatedly - that is one possible design our team has considered. However, we've come to the conclusion that there are definitely better solutions.

[bobdahaxor]

when you decide what you want to do, think about the weight of the ball. The ball is 10 pounds and 40 inches in diameter. that is quite heavy. If I were you,I would make a list of the pro's and con's of each type and then make a list of what you want your arm to do. Then compare the pro's and con's list to the list of what you want the robot to do. Besides that, I want to warn you that scissor lifts are extremely hard to properly manufacture. I also did the math for the spring (gotta love physics 201 and oscillation's and elasticity) and pushing or punching the ball is out of the question. There is not enough of an impulse to do so. I have a hint though (or for what I think is a good idea). That 8020 you got in the KOP is more than likely just sitting there. It can easily be used as more than just a square tube.

[Storm]

My Team did a Scissors lift in 2005, it worked, but it took massive amounts of time and most of it had to be custom machined by one of our sponsors. It took a huge ball screw to actuate and we had a high CG. on the other hand it won the Engineering Inspiration award. Here is a picture.
After that we have the "no scissors" rule like many of the other teams.

[Cartwright]

After a week of brainstorming and prototyping..we're thinking hard about a chained lift. The only time we've ever done a scissor jack lift was the '99, Cyber Blue's rookie year. We did a chained lift in 2005 for lifting the tetras and we think it will work quite well for this year. I think the biggest thing this season will be how you grip the ball really. I mean it really doesn't matter how you get it up there as long as it works and its fast. I think the real matter is once you get it up there, can you place or throw the ball? Will the gripper/holder make it too top heavy?

[graymorr]

Any chance to get more pictures or drawings of your 2004 scissors lift. You have brackets on there for some reason(s). Gray

[hipsterjr]

I have been curious as to exactly how much force it would take to launch a ball 10 ft at a 60 degree angle. ( for about 7ft high and between 5 and 7 ft horizontal from overpass.) I think arms and lifts are going to be too slow.

[dtengineering]

Originally Posted by hipsterjr

I have been curious as to exactly how much force it would take to launch a ball 10 ft at a 60 degree angle. ( for about 7ft high and between 5 and 7 ft horizontal from overpass.) I think arms and lifts are going to be too slow.

Take a look in your physics textbook for kinematics formulas. The math to solve these types of problems is quite simple and is a common part of the Physics 11 curriculum here in BC. My estimates are that to launch the ball six and a half feet (roughly 2m) requires an accelleration of 2g over a distance of 1m.

In other words if you have 20lbs of force behind the ball for about 40" you should be able to get it to go 6 1/2' straight up from the last point you contacted it. To account for your desired 60 degree angle, take a look at breaking a vector down into orthogonal vectors (ie, how much "up" and how much "over" you will need). These are actually quite useful formula for many types of questions and are not that difficult to use and understand.


Jason

[Cory]

Never use scissors lifts is a cardinal rule on our team.

[thefro526]

we used a scissor lift in our 04 year that was plenty fast but it wasn't strong

[Peter Matteson]

Originally Posted by Cory

Never use scissors lifts is a cardinal rule on our team.

For our team too.

[Dan Richardson]

4 Bars With Gas Springs have been used before, and quite effectively. However I feel like not in the way your describing.

http://www.chiefdelphi.com/media/photos/26796

http://www.chiefdelphi.com/media/photos/21477

http://www.chiefdelphi.com/media/photos/27982

Thats 1902, 1369, 217 in 2005, 2056 in 2007 just a few examples that I can think of.

[JHSmentor]

Originally Posted by Stud Man Dan

4 Bars With Gas Springs have been used before, and quite effectively. However I feel like not in the way your describing.

http://www.chiefdelphi.com/media/photos/26796

http://www.chiefdelphi.com/media/photos/21477

http://www.chiefdelphi.com/media/photos/27982

Thats 1902, 1369, 217 in 2005, 2056 in 2007 just a few examples that I can think of.

These are great examples of 4 bar designs - does anyone have some CAD drawings that we can look at for how to opperate something like this (mechanically)? We are a new team and are tossing a lot of ideas around but don't have enough knowledge on any one system to make a good guess.

[Cartwright]

I'm interested why those are your four options. Why not some sort of grabber? A scissor lift is quite difficult and a crane seems quite unwieldy. I don't know...we've not decided on our design, but we haven't really considered lift systems much.