Measuring projectile poof balls

[mechanicalbrain]

I have to say that's the best title i've ever used! According to the rules the balls can have a max speed of 28mph or 12 m/s. Obviously this is a important rule since it insures safety. It occured to me however, how do we measure the velocity of the balls?

[Tom Bottiglieri]

If you are using a pitching machine type device, you can use rotational motion principles.

V = r ω

V - Linear Velocity
r - Radius
ω - Angular Velocity

So, find the RPM of the output wheel, convert to Rotations per Second, then convert to radians per second. ω is a unit of radians per second.

That should give you a basic outline of how fast it will travel assuming a 100% efficient transmission of power between both items.

[Sscamatt]

Bushnell Velocity Radar Gun


"Baseball Accuracy: +/- 1 mph
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Auto Racing: 6-200 mph/16-320 kph (1300+ feet away)"

http://www.dickssportinggoods.com/pr...ductId=1845491 I've seen it at RadioShack as well, eBay has them for ~$80

----------------------------------------------------------------

SPEED WATCH


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[mechanicalbrain]

Thanks both. That's one concern out of the way. Now number 204....

[Rickertsen2]

well there are a few ways. If you can shoot your launcher straight and measure the height it reached then use the formula v=sqrt(2gh)

it was derived from conservation of energy
kinetic energy = (mv^2)/2
potential energy =
mgh=(mv^2)/2
2mgh=mv^2
2gh=v^2
v=sqrt(2gh)

If you can't launch straight up but can launch straight ahead and measure the distance it fires from a known height then:

v=d/(.45sqrt(h))

where h is the height between the launch point and the floor. d is the distance traveled before hitting the floor. Everything must be in SI units.

[sciencenerd]

Our team is using a video camera with frame-by-frame analysis to figure out all the characteristics of the foam ball. If the Boeing engineer says it's possible, I'm going to believe him.

I'm so glad the fields are indoor, having to deal with wind would be a nightmare...

[gburlison]

We might just try this:


<S02> Muzzle Velocity - No ROBOT may throw a ball with an exit velocity of greater than 12 m/s (26.8 mph).
As a reference, a ball traveling at this velocity when leaving the ROBOT at an angle of 30º from
horizontal with no spin will travel approximately 35 feet. A robot that violates this rule will be
considered unsafe per <S01>.

[mechanicalbrain]

Originally Posted by gburlison

We might just try this:


<S02> Muzzle Velocity - No ROBOT may throw a ball with an exit velocity of greater than 12 m/s (26.8 mph).
As a reference, a ball traveling at this velocity when leaving the ROBOT at an angle of 30º from
horizontal with no spin will travel approximately 35 feet. A robot that violates this rule will be
considered unsafe per <S01>.

Which brings up concern 204! We talked about putting a spin on the balls but were not sure if it would do more to hurt then help.

[Cyberguy34000]

Heheh this year the matches are going to be NUTS! Volunteers will be running all around the sides of the field throwing balls that bounce out back into the field. Balls will be flying everywhere. None of the balls wil be allowed to go that fast, but 12 mph is still fast enough to take out a few unattentive judges

Let the chaos begin!

[Billfred]

Originally Posted by Cyberguy34000

Heheh this year the matches are going to be NUTS! Volunteers will be running all around the sides of the field throwing balls that bounce out back into the field. Balls will be flying everywhere. None of the balls wil be allowed to go that fast, but 12 mph is still fast enough to take out a few unattentive judges

Let the chaos begin!

Careful on the units--that's twelve meters per second.

[Nuttyman54]

you could always use the beam sensor (parts KR61 and KR62). set the beam across the ball path, and have it measure the time during which the beam is broken. Combined with the ball diameter (7") you can figure out the velocity

[Daniel Brim]

Originally Posted by mechanicalbrain

Which brings up concern 204! We talked about putting a spin on the balls but were not sure if it would do more to hurt then help.

I think that the proper spin would help more than hurt. If you launch with no spin (which is possible), I think that there would be a "knuckleball" effect, where the ball would basically dance and repeatability would be low. However, if you put the right spin, the ball travels further and in a more predictable trajectory.

The best way to find out? Prototypes!