12-02-2007 13:08

MrForbes

Re: pic: FRC488 - Lifts Raised 1

That's really neat! do the unfinished details include something to keep robots from driving off the back or rolling back down the ramps?

12-02-2007 13:21

Madison

Re: pic: FRC488 - Lifts Raised 1

There is a portion of each platform that sits on the prongs poking out toward the wall missing. There's no plan to include anything to stop folks from driving off the non-ramp side simply because our experimentation has shown that it's not necessary.

This video demonstrates how simple it is to drive up and stop on the platforms, I think. Shown is our 2006 robot, driven by a student with less than 10 minutes worth of experience driving. The robot starts approximately one-half of a field length away in a random orientation and our student was able to drive to the ramp and climb it in one try, taking less than 15 seconds.

A more experience driver should have no trouble with this and they wouldn't even need to worry about making a 90* turn during a match as our driver did here. I've been estimating that it'll take no more than ten seconds for our partners to situate themselves safely on our lifts. The platforms will raise no matter where their robot ends up as long as its center of gravity is somewhere over the lift.

If it turns out that teams are having some trouble with stopping in place, we'll park closer to the wall

12-02-2007 13:30

MrForbes

Re: pic: FRC488 - Lifts Raised 1

Ok, I was just thinking about last year, robots slamming into the wall at the back of the platform at full speed as the buzzer rang....10 seconds is a long time to not be scoring!

12-02-2007 13:39

Madison

Re: pic: FRC488 - Lifts Raised 1

I think very few robots, even in the upper eschelon of competition, took fewer than 10 seconds to commit to and successfully climb atop the ramp at the end of a match. I don't think it's unreasonable to allocate about that time for most robots to able to move from anywhere on the field onto our platforms. Only if it's possible for a robot to turn a row of 5 into 6 is it worth the time to sacrifice the lift and try to score.

12-02-2007 13:52

Jeremytice

Re: pic: FRC488 - Lifts Raised 1

Very cool...Good job you guys, it looks great!

12-02-2007 16:56

Joe Johnson

Re: pic: FRC488 - Lifts Raised 1

No arm? Bold indeed.

What motors are you using to lift 2 190lbs 12inches in 2 seconds?

Force = 380lbs = 1700N
distance = 12 in = .3m
Work = 4600in-lbs = 510 Joules
Power = 260 Watts

You had better say something like "The Big CIM" or 2 FP's or something else that adds up to enough power to do the job.

Joe J.

12-02-2007 16:59

Lil' Lavery

Re: pic: FRC488 - Lifts Raised 1

They're using gas springs.

12-02-2007 17:06

Joe Johnson

Re: pic: FRC488 - Lifts Raised 1

Those Laverys... ...you can't turn your back on them ;-)

I was just about to correct my analysis (after blowing up the photo to see it better) when I notices that Lil' L just called me out.

Ah well... ...it is hard to argue with the truth.

A typical gas strut about that size has a stroke of about .2m and has a force of about 1000N. That means each spring is packing 200Joules. They've got 4 of them so it should be able to provide 800 joules or so. Plenty.

Very good,

I have another question. How do you tie the front an the back together? If I am a very heavy robot in front and light in the back will you lift me still or will the platform $@#$@#$@#$@#?

Do Tell.

Joe J.

12-02-2007 17:06

Madison

Re: pic: FRC488 - Lifts Raised 1

Each lift is driven upward by two 125 lbf. gas springs. Each spring is held closed through the match by a servo-driven latching mechanism that is designed to distribute the force of the springs into structural members of the lift rather than directly against the servo.

You can see a quick video taken without the latches attached that shows two students setting and releasing the lift here: http://www.youtube.com/watch?v=okYnM1a5T-E

Each spring drives a four bar linkage such that there are two linkages per lifting mechanism. Those linkages are tied to one another in several places throughout -- three crossbeams supporting the polycarbonate platform attach to the upper horizontal member of the four bar, a single crossbeam connects to the bottom of the four bar, and a larger crossbeam connects each side at the gas spring end to give rigidity near the points that allow the lifts to rotate from vertical to horizontal while being deployed.

The platforms are very good at handling uneven loading, as you can see for a moment in the video linked above when the students press downward unevenly. We've tested the lifts with three 50 lbs. sandbags in as many different locations as possible. As a result of such testing over the last week, we identified some problems with lifting robots with CGs in certain places and redesigned and rebuilt the mechanisms to compensate.

12-02-2007 19:35

Matt Reiland

Re: pic: FRC488 - Lifts Raised 1

Very nice and well thought out!

12-02-2007 19:40

silicon_ghoti

Re: pic: FRC488 - Lifts Raised 1

That's really nice, you guys have always done a very nice job of designing and building your robots. I can't wait to see that operate during the real thing. See you guys in Portland.

13-02-2007 16:39

Cody Carey

Re: pic: FRC488 - Lifts Raised 1

Careful about that, because if the robot slams into the wall and ends up touching it after the match, doesn't that mean that you don't get the bonus points?

14-02-2007 13:09

Madison

Re: pic: FRC488 - Lifts Raised 1

It's extraordinarily easy to stop somewhere on the ramp. They're very, very big.

In any case, we're adding a stop along the backside to give robots a little bit of incentive to stop.

14-02-2007 15:51

fluffy

Re: pic: FRC488 - Lifts Raised 1

If you put up a sheet of cloth or something of that sort on the side of the ramp closest to the wall, then you wouldn'y have to worry about robots accidentally touching the wall as they would touch the cloth instead...just a thought