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

Greetings fellow mech-maniacs.
Our team is in somewhat of a pickle this year, since we can't quite agree on what would work best. I've presented the concept of a 4-bar lift (used in some heavy industrial forklifts), which would be capable of lifting the ball to overpass level via worm-gear or lead-screw, and then releasing it to complete the hurdle.
We are also debating the use of a scissors-lift, although I am not very fond of them because of the large amounts of force necessary to lift them from compacted positions, and starting them from semi-open positions means they are taller.
We were thinking about using an angled crane which sloped back over the robot, potentially mounted on a scissors lift to carry it the extra few feet to the overpass, but I think that might be rather complex, and we've had bad experiences with complex machinery.
Finally, we were thinking of a combination of a 4-bar lift and a gas-spring. The lift would center the ball over a motor-wound gas-spring, which would then fire and kick the ball over. I'm skeptical about it, because our '06 tests showed that pneumatics and the like were barely capable of firing a poof-ball, let alone these new trackballs.
Any comments to help settle the predicament would be VERY welcome!

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

Can you build some quick mockups to test some of the different ideas?

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

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

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

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

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

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.

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

The biggest thing I can advise you keep an eye on is where your designs put your bot's CG... too high and you're in danger of tipping, and unless your manipulator is also able to reorient your bot, your match will be a disaster. The inner tubes from last year weren't all that heavy, but the trackballs this year are pretty big; the difference between the CG of an unladen robot with its manipulator at full vertical extension and the CG ofa laden one in the same configuration is probably going to be substantial.

Anyway, your team has probably already thought of most of what I'm about to say, but just in case...

The scissor lift is good if you want your bot to have a low profile without a trackball; you can get a lot of vertical height out of an extended scissor lift for relatively little height in its starting configuration. The main drawbacks are power and speed, though. It takes a lot of power to get the lift going, and you'll probably have to gear down a motor (maybe a worm gear or something similarly drastic) or use a lead screw, both of which sacrifice a lot of speed. It's also a pretty tough task to build a robust scissor lift that is also mass-efficient.

The four bar linkage sounds viable, but depending on where it sits on your bot it could wreak havoc on its balance. Hold the trackball too far out in front of the bot, and you're all but asking it to fall forward. On the plus side, this sounds much easier to implement than the scissor lift.

The crane seems like a good idea balance-wise, but it would need to be robust. Team 1757 used a crane-like system last year with a claw on the end; we'd definitely be able to lift an inner tube over the overpass, but I don't think it's tough enough to lift a trackball.

My last word of advice is not to combine lifters! Not only does that fly completely in the face of K.I.S.S., I would bet you'd see a significant rise in man-hours required both for design and fabrication, and then for integration. It could certainly be done, but I think you'd need to be pretty confident...

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

I forgot to mention the gas spring idea, but that's because it's beyond my ability to even think about designing something like that. I can say that one of the teams at the 2006 Boston Regional had a pneumatic poof ball launcher that could score from about half court, so I feel like you could get some pop out of one.

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

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

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

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

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

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

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

For our team too.

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

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.

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

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.

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

I agree, never use a scissors lift.

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

we had to learn that the hard way :( although it was extremely powerful, enough to lift a 150lb person. but it was slow and heavy..
you can look at my avatar thats the bot, it does look cool though.

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

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.

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

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).

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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?

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

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

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

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.

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

id say use the forklift

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

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

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

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.

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

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

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

we used 120lbs gas springs last year for our rams........... never again, be burn out a drill we used to get them to shut.