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

[Ianworld]

From my experience almost every rookie team has to build their one scissor lift to learn firsthand why they're a tough choice for FIRST. In almost every robot situation a different mechanism will be just as effective and really the key point easier to make. A scissor lift requries a large amount of careful machining and has certain issues such as how to start it and stability when fully extended.

I'm a big fan of keeping things simple. This year the object is spherical, a 4 bar linkage on the arm isn't necessary. The main advantage of sucha mechanism is that it keeps an object at one end level throughout the whole motion. A ball is a ball no matter which way you rotate it.

Anyhow think simple and functional. I'm a big fan of just simple rotating arms. You just need to think of the torques and the power necessary to move a ball at a distance.

[AdamC]

Thank you all. We've become very interested in a gripper that pinches the ball from the sides, and retracts into the body of the robot to secure it. It's a real debate as to whether or not we should hurdle the balls, or if just having a powerful robot that can push impeding robots out of the way and run lots of laps. I have a personal want to hurdle, because with 6 robots on the track, running a lot of laps is highly unlikely.
If we do go for hurdling, it will probably be an articulating arm, somewhat along the lines of (I believe it was Swampthing's) robot in '04 (or was it '01? I'll check on that).

[Phil Ross]

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.

you have to be careful when "launching" if you endanger other robots on the feild and other feild components you are going to have a bunch of reffs telling you to do something about your manipulator.

[hipsterjr]

I've heard from others that have tried that launching via pneumatics won't work well.

As for everyone putting down scissor lifts, we built one our rookie year (2000) and won the rookie all-star award and made it to the Florida regional finals. It is possible to make a good scissor lift.

[lukevanoort]

Originally Posted by wadidievrdo2u

you have to be careful when "launching" if you endanger other robots on the feild and other feild components you are going to have a bunch of reffs telling you to do something about your manipulator.

I think you are committing a judgment error that I have noticed many on my own team doing. Just because the ball is HUGE, doesn't mean it is necessarily more destructive than a smaller object. Consider this, a trackball (assuming 8lbs, which, from the reports here, seems to be a more accurate weight than the 10lbs the manual reports) traveling at a rather fast speed of 5m/s (11mph or 16ft/s) has roughly the same kinetic energy as fully laden robot (120lb robot + 13lb battery + 15lb bumpers = 148lbs) traveling at 3.7 ft/s. I know from personal experience that FIRST fields can take impacts by object with a more KE than the ball without breaking. Robots... I can see them being damaged, but that is just part of the challenge of game. Build 'em robust, folks.

[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.

[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?

[fordchrist675]

scissor lift is also not that sturdy given you have to lift a 10 pound ball up 7 feet kind of a challenge but hell more power to you. crane top heavy, 4 bar lift possible


a forklift hey theres an idea haha

[Bomberofdoom]

Think it's been said in this post before, but our team discussed some of the ideas, especialy the crane idea, and we found out that the crane that we would might want to use would require a 12.7 battery at the back of the crane because of power and balance (center of gravity) issues. It came out to be too dangerous and unreliable.

So IMTeam'sO, don't go for the crane.

[Urban Hawk]

id say use the forklift

[BK Lounge]

i am researching the scissor lift right now. what is the best way to extend it.

[lukevanoort]

You could likely end up getting similar performance by not building it at all. Seriously, scissor lifts probably have the highest failure rate of any design commonly used by FIRST robots. There may be effective ones, but I have never seen one in person.