Horizontal Bar: Vertical Velocity

[andy]

sorry i couldn't resist

V^2=Vo^2+2aX

btw all numbers in metric. metric system rules!

where
V= final velocity
Vo=initial velocity
a=acceleration
X=Delta X (change in position)

V^2=0+2aX
Vo=0 m/s because the projectile starts at rest

V^2=2*9.8*X
a=9.8 m/s^2 acceleration of gravity

3.048^2=2*9.8*X
V=3.048 m/s = 10ft/sec metric rules! remember!

solve for X
X= 0.473995102 meters
X= 1.555102 feet

Remember METRIC RULES!
Good luck this year!

-Andy

[mtrawls]

Originally Posted by tkwetzel
This is interesting, because this maximum velocity is relative to the robot. They did not think this through, because technically, whatever is being sent over the bar is part of the robot.

Technically, thou sayest? What dost thou mean with this "technically"? Really, I seemed to get a slight perception that FIRST wanted us to exercise common sense (something in there was vaguely about safety I think), and there was some statement degrading lawyers (alas! my future profession). Really, though, Dean explicitly said not to over-interpret the rules -- he said that he uses words to "mean what they mean" (stradling is stradling, for crying out loud). I for one like the idea of a minimalist rules book. I mean, 3 rules for scoring! 3! I could barely believe it.

sorry i couldn't resist

I feel your pain. I as well cannot resist (my physics teacher must have done something right ... or would that be wrong )

Anyway, let's see some accuracy. Why assume that U=mgy is "good enough" afterall! So,

dU = GMm/r - GMm/(r+y) = 1/2 mv^2

(dU means delta U, G is gravitation const., M is mass of earth, r is radius of earth, ..)

Upon solving, y = 5.10! Considerably less than 5.55. I used the values,
G = 6.67 * 10^-11
M = 5.98 * 10^+24
r = 6.38 * 10^6

(something I'm not remembering right from all the physics lectures I slept through?)

[Skabana159]

Of course, you are all assuming that the object, let's call it "projectile," is decellerating at the gravitational constant! If you were to give it the initial velocity of 10 ft/s, as well as give it an acceleration in midair somehow (get to that pneumatics drawing board), you would be able to send it wherever you wanted to! Particularly if you were to give it an acceleration of, oh say 9.81 m/s/s.

[Greg]

Yes, I found this suggestion about a camcorder too. Still, it does not explain what the velocity is relative to. In the test with the camera the bot would be standing still, and in the game it might be moving. As well, testing would be needed to see how far you can actually throw something with that velocity It may sound like a lot but there is really no way to tell...

Well, anyway, Dean did talk about generalizations in the rules and how we should not read them the way lawyers do So Im guessing my team will just figure it out eventually

[Kevin Kolodziej]

Rule <G08> states: Mechanisms which interact with the Pull-Up Bar are limited to a maximum tip velocity (relative to the ROBOT) of 10 feet per second.

Two questions:
1) Does tip mean the tip of a projectile or does tip mean tipping as in falling velocity?
2) If it is the latter, wouldn't that eliminate the possibility for all bar interaction? Your robot has to extend to 9' to get to the top of the bar and if you are tipped, the top part of your robot is certainly coming down at a velocity greater than 10 ft/s.

I'm really trying to simply interpret the rules, but tip is a bad word to use.

Kev

[George1902]

They mean the tip as in the farthest part of your climbing device. It cannot extend or retract any faster than 10 ft/sec.

[Greg]

And one more question. I think in the video it was said that the "maximum vertical velocity cannot be greater than 10ft/sec". If so, what if the robot launches the projectile at an angle, and not straight up? Is only the vertical component counted? The suggested way of measuring velocity (with the camcorder) would probably do just that.

[patTeam241]

I'm still not real clear on this, you can move upward at 10 feet per second, which roughly translates to 1.5 ft/sec. I have two questions on this.

-First, if you extend an arm, this is not influanced tremendously by gravity (unless i'm mistaken), so that should rise closer to 10ft/sec.
-Second everyone is mentioning it going 1.5 feet, on the same arm theory, you could move this for more than one second correct.

Just trying to get a little clarification.

[Wetzel]

Originally Posted by Greg

And one more question. I think in the video it was said that the "maximum vertical velocity cannot be greater than 10ft/sec". If so, what if the robot launches the projectile at an angle, and not straight up? Is only the vertical component counted? The suggested way of measuring velocity (with the camcorder) would probably do just that.

It still can not excede 1.5 ft verticaly. Gravity is accerating all objects downward at a constant 9.8m/s^2. (mixed units work, right?) So anything only given the maximum velocity at the begining of the movement, like a ninja grapling hook, would only be able to travel 1.5 ft verticaly, no matter the angle.

Arms that swing up need to calculate the tip velocity and the end of the arm, and limit it to less the 10ft/s. Arms that move verticaly should take more then 1 second from the carpet to the bar, there abouts when moving from a starting height of 2-4 feet.


Wetzel
~~~~~~~~~~
These equations are easy and you should learn them all in physics.
I've never taken physics.
Acutally, I'm going right now to see what physics classes are still open and maybe add it this semestor.

[Gabe Salas Jr.]

The Vertical Velocity Limit is implemented so that teams do not design a robot that may attempt to launch a teathered artillery grappling hook to the bar from a long distance off the field. Although it would be nicely done by triangulating your distance using the IR sensors, and making a program that automatically adjusts angle and power to the artillery cannon on your robot. So if for some reason you missed, it was the programmers fault. Just kidding.

...and it would not be a good idea if the robot went insane during the match, and aimed the cannon to the audience...

But really, it is just for the safety of the drivers/human player, the refs/judges, and more importantly, the audience.

[Nick R.]

i dont think they would allow us to jump ONLY 1.5 feet if the bar is about 10 feet high and there is a restriction on the hight (60 inch) as usual..
what i suppose they mean -with regards to relative velocity is that we should use our robot base as the reference point though this would only affect the horizontal and not the vertical velocity of whatever it i being shot up(unless the robot is jumping up and down... )
i think we're going to try and go about it with a spring.. use the energy conservation concept to make sure that the release velocity is not going to be over 10 ft/s which is quite reasonable since its about 2.5-3.0 m/s
and we have to account basicaly only gravity and the tension created by the wire or cable(that will be used to pull it up) to analyze the 2 dimenional projectile motion of the hook/grabber

"simple, but not ordinary" Mr Keeting - "Dead Poets Society"

[sevisehda]

The restriction on hieght only applies to the start of the match. So if your robot could double in height during the match, it could grab the bar without having to use a grapling hook.

Keep in mind the vMax only applies to a grapling hook or arm. If your entire robot were to jump then you could jump any height you wanted.

[Gary Dillard]

I'm thinking we'll need to wait for clarification from FIRST on this one. If it's really just maximum vertical velocity (as they mentioned in the video), I could lift a cannon 10 feet and shoot a projectile at the bar for zero vertical velocity. If it's tip velocity (as in the safety concern they discussed), then the maximum distance you can shoot it up is 1.55 feet times the sin of the angle at release (straight vertical being 90 degrees and the farthest distance).

[Mike Betts]

Originally Posted by Nick R.

i dont think they would allow us to jump ONLY 1.5 feet if the bar is about 10 feet high and there is a restriction on the hight (60 inch) as usual..
i think we're going to try and go about it with a spring..

Nick,

I would imagine that this would (and should) be disqualified. The spring may be dangerous (in the view of the inspectors) if it goes off in your face...

I do not think that they want projectiles. Period.

However, they are allowing a "small" projectile that would not cause great concern to spectators, players or referees...

As a member of a team who, in 1994, made a catapult capable of launching a 7 pound ball 30-40 feet, I can testify to the incredible power which could be stored and then released by these robots.

That particular robot was a crowd pleaser but it scared the heck out of me (and the officials). The spring mechanism was made from the 10 feet of latex tubing in the kit and the bands broke under tension (a lot). Not to mention that sometimes the match would end before we fired (but the mechanism was armed) and the field team had to remove the robot and hope that it did not go off in their face.

Any engineer who can't design a "safe" thin arm to deliver a cable (attached to a winch) to the bar needs to go back to school.

Let's all stop being lawyers... When we design these systems ask " would I want my Mom (or daughter) standing next to this thing when it goes off?".

[/end soapbox]

[Wetzel]

Originally Posted by Mike Betts

Nick,
Any engineer who can't design a "safe" thin arm to deliver a cable (attached to a winch) to the bar needs to go back to school.

Let's all stop being lawyers... When we design these systems ask " would I want my Mom (or daughter) standing next to this thing when it goes off?".

FIRST dosn't need be concerned with what an engineer can or can not design safely, but what students can safely design. Teams have alot of different ways of design, from engineers and students working side by side, engineers watching and pointing things out, to no engineer support, to totaly engineer designed.

Nice play on the GP saying.

Wetzel