Re: Springs?? (10 lbs. at 22 ft/s)
 

22 ft/s is about 6 or 7 m/s

(English units vs. metric units)

Re: Springs?? (10 lbs. at 22 ft/s)
 

Whoops :o

Re: Springs?? (10 lbs. at 22 ft/s)
 

Well I guess it's safe to say that the majority of us agree that any type of spring would be dangerous to use for this. The massive amount of force required requires a LARGE spring which are dangerous.

What I find interesting though is that so many people are getting different energy requirements for launching it though. I've seen numbers ranging from 5 J to 80 J. I know it depends on the angle but my teams estimated 7.5 J at 65 (I think degrees) is vastly different then then post above that gives that 80 J estimate.

Re: Springs?? (10 lbs. at 22 ft/s)
 

If you figure that the mass of the ball is ~3.5 kg and you want to shoot it to a height of 2.5 meters (a little over 8 feet) then:

(3.5 kg)*(9.8 m/s^2)*(2.5 M) ~ 86 Joules

This is assuming that the horizontal componant of the balls velocity comes from your moving robot.

(posted by s_forbes on dad's computer)

Re: Springs?? (10 lbs. at 22 ft/s)
 

I believe you've misread the definition of CROSSING. For "it", read "line". The definition refers to projecting the line to indicate a theoretical flat surface through which a ball or 'bot will move. Imagine light shining straight upwards from the line. It's not talking about throwing the ball.

Re: Springs?? (10 lbs. at 22 ft/s)
 

squirrel I am with you 100% on this one. I do not see this being a safety hazard if design correctly.

And as for some of you people who are thinking of a large spring being pulled back to hit the ball with brute force, i think you should try thinking outside the box for a few ;).

Re: Springs?? (10 lbs. at 22 ft/s)
 

What if you were the inspector, what would you be looking for?

How secure is the spring attached to the robot?
How secure is the launching pad between the trackball and spring?
What has been done to protect against pinch points between the launcher and robot?

These are just a few of the questions I would have (not and inspector). What other ones could you ask.

Aside: Putting your robot on display (grade schools, sponsors etc) will be a riot if you can hurdle the trackball 7-8 feet in the air! The only problem will be getting that blasted 41" trackball through a standard door.

Re: Springs?? (10 lbs. at 22 ft/s)
 

If you're imparting 100-200 joules into the ball, be sure that the centerline extends back inside the wheelbase, or do the math carefully so your bot doesn't do a back flip.:yikes:

If I were an inspector, I would also try to be sure that nobody's head is likely to be launched instead of the ball.

Re: Springs?? (10 lbs. at 22 ft/s)
 

How would we go about testing the amount of force needed to propel the ball 8 feet in the air and once we go about testing that, and based on that calculation how would we quantify that in order to find how much energy would have to go into the ball? For example, we did a lever arm experiment where a mentor jumped on a lever and the ball was on the other side. We have the numbers and have calculated the energy lost from the jumping onto the lever to the ball leaving the lever. But we don't understand where to go from that point and I also don't believe that we calculated correctly. Any help would be greatly appreciated. Also based on that number, how do we determine what strength of spring we need.

Re: Springs?? (10 lbs. at 22 ft/s)
 

As an inspector, in addition to the intended function of the launcher, I would look for possible unintentional means of sudden release of this stored energy. Having a strong spring release accidentally while the robot is being carried on the field or in the pits can have very dire consequences. FIRST inspectors must decide whether your launcher is safe and that is a subjective judgment call. Expect to show the inspector how the spring can be inhibited from releasing accidentally (including failure of the firing restraint), how you can slowly/gradually release the energy in case you don't want it to fire and how the launcher responds when it fires without a ball.

You're probably not going to find a written, official checklist from FIRST, so you have to keep asking yourself what can go wrong and how can I avoid accidents as you design your launcher.

Re: Springs?? (10 lbs. at 22 ft/s)
 

This is my point. I'm not trying to rain on anyone's parade, but better to hear it now than to get to competition and be disqualified for safety reasons (so that you have to dismantle your launcher and just be a race-bot for the rest of the tournament).

I did the math at 45 degrees and 2.5 meters and found the initial kinetic energy requirement to be 221 Joules (accounting for reasonable assumptions on energy loss, etc.).

I think that teams who try this method will (a) be disappointed in just how -hard- it is to throw that ball with a robot and (b) will be disqualified from play until they disengage their springs.

That said -- more power to you if you want to try.

Patrick

Re: Springs?? (10 lbs. at 22 ft/s)
 

I think that you'll be amazed at the designs the different teams come up with to solve this challenge....putting twenty or thirty thousand creative minds to work to solve a problem can result in wonderful things.

Re: Springs?? (10 lbs. at 22 ft/s)
 

Patrick,
I think you need to sit back and think long and hard about what you just said, especially to other young minds around this forum.

"That said -- more power to you if you want to try"

Do you know how many great inventions probably started with the exact same sentence?? I would bet almost all of the great ones.

Teams WILL throw this ball, and teams WILL do it safely, and teams WILL do it effectively.

The bigger the risk, the bigger the reward...

For the teams jumping "into the deep end", we're with you, and we're proud..


Brando

Re: Springs?? (10 lbs. at 22 ft/s)
 

I'd love to see it, and I hope it works out well -- nowhere in my remarks was I being in any way sarcastic. I wasn't even being _pessimistic_.

It is not unreasonable to point out that certain approaches are harder than others, and also that the act of physically launching the ball carries a great deal more safety issues tied up in it than lifting the ball in some manner.

I certainly _do_ hope to see safely-launched balls. I certainly _do_ hope that all teams rise to the challenge of this game in the best way that they know how. I certainly _do not_ want to see teams that cannot hurdle at all because they haven't fully considered all of the ramifications of their approach, and now have a robot that will not be allowed to play based on safety concerns.

How awful would it be to show up with a fully-functional, killer-app bot and then not be allowed to use it? The fact that the judging of the safety is both discretionary and subjective just means that even more caution needs to be taken.

It _is_ quite amazing what thirty-thousand minds bent to a single task can accomplish. I'm sure some teams will pull off safely-launched balls, and be both effective and amazing. I'm *not* so sure that they'll do it with a spring capable of throwing 10 lbs at 22 ft/sec, which is the topic of this thread.

Patrick

Re: Springs?? (10 lbs. at 22 ft/s)
 

I think you're probably right about it being quite difficult to do this safely with a spring.

Which is why I suggested considering using something else (perhaps compressed air?) instead....here where those folks thinking about using a spring might be likely to see it.

Anyways, if you are a team that is thinking of shooting the ball using a spring type mechanism, it might be wise to post your ideas here so others might be able to point out safety issues, or suggest other ways to do it better. My opinion is that you have little to lose by posting your designs, and a lot to gain if it helps you improve it in ways you didn't realize it could use improvement.