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Re: Trajectory B/C
Posted: January 26th, 2010, 4:37 pm
by zyzzyva980
So there is absolutely no way to fix this mechanism that is loose? Nonsense! There is always a way!
Re: Trajectory B/C
Posted: January 26th, 2010, 5:14 pm
by andrewwski
inycepoo wrote:If you haven't noticed yet, I use a cannon/Push device, I'm including the link to my Photobucket if you want to see more pictures.
To what height can your cannon push device reach? I've always used a catapult-like design and last year at States they elevated the close target to 2.5 meters, and most of the push devices I saw couldn't make it to the top of the platform. The catapult's parabolic shaped arc lets you reach maximum height and distance, especially when placed at the right angle.
Last year's rules were the same as this year's - the maximum height of the close target is 2.0 m.
While it does seem like a catapult would give you more of a parabolic shaped arc because the projectile is being moved in an arc already when it's launched, that's not actually the case. After the projectile leaves the device - whether it is a catapult or slingshot/cannon type device, it is going to take on a parabola shape regardless. It will have a steady horizontal velocity and no horizontal acceleration (except deceleration due to air resistance), and an initial vertical velocity plus acceleration due to gravity (in the opposite direction). This leads to a parabolic arc.
Re: Trajectory B/C
Posted: January 26th, 2010, 6:33 pm
by starpug
RndmPplPrsn wrote:If you look closely, in the back of my design there is a black "Swivel Latch." It is loose and shaky (Its own mechanism, not how I attached it), so in other words my "Cannon" (I call it the Launching Module) goes left to right easily. It was also very hard to construct for it to even be remotely close to straight.
If you don't know what I mean by "Swivel Latch," here is a picture, it's on the left side.
http://www.wildwesthardware.com/hinges/ ... _KIT_8.jpg
I also had a sort of epiphany while beginning on new designs after invitationals, I recognize in some manners in how the cannon is shot, leaves a lot of factors for the projectile to move horizontally, when not meant to. While the pull devices, if built decently enough, seem to always be relatively straight (Horizontal movement is less than 5cm). When building even the perfect push device, there is still a considerable horizontal movement. So for my pull design, is there a "best" way to assemble the elastic solid where I can easily, quickly, and repetitively (Without Tear & with Consistence) launch my device (Ex. Cotter Pin, Certain Latches)?
There's a different kind of latch which I have used for similar builds. It's called a gate latch and it looks like
http://www.modsbymax.com/_photos/BedLCD/GateLatch.jpg If you take the little hook piece (not the bar) and put some sort of thing on whatever you use to push the ball out of the device to allow the latch to hold onto it, you have a pretty good launching device.
Re: Trajectory B/C
Posted: January 26th, 2010, 9:00 pm
by RndmPplPrsn
Thanks Starpug, and Andrewwski is correct. By the time most of y'all will take Physics, trajectory won't be an event anymore. Kinematic equations are a savior if your device is precise enough, just do a couple calculations and equations on excel, and all of the work is done, with enough test shots provided.
Still does anyone have any ideas/ever attempted battery start. I have no real way of making one, except an idea that there would be a loose pin in the mechanism, and a laser on that, so when removed it senses it and launches the device.
Re: Trajectory B/C
Posted: January 27th, 2010, 8:47 am
by inycepoo
andrewwski wrote:inycepoo wrote:If you haven't noticed yet, I use a cannon/Push device, I'm including the link to my Photobucket if you want to see more pictures.
To what height can your cannon push device reach? I've always used a catapult-like design and last year at States they elevated the close target to 2.5 meters, and most of the push devices I saw couldn't make it to the top of the platform. The catapult's parabolic shaped arc lets you reach maximum height and distance, especially when placed at the right angle.
Last year's rules were the same as this year's - the maximum height of the close target is 2.0 m.
While it does seem like a catapult would give you more of a parabolic shaped arc because the projectile is being moved in an arc already when it's launched, that's not actually the case. After the projectile leaves the device - whether it is a catapult or slingshot/cannon type device, it is going to take on a parabola shape regardless. It will have a steady horizontal velocity and no horizontal acceleration (except deceleration due to air resistance), and an initial vertical velocity plus acceleration due to gravity (in the opposite direction). This leads to a parabolic arc.
Yes, simple kinematics tells you that. But I've tried it with a pull cannon method and didnt' get as much height as I've gotten with the catapult. Maybe my design was off or something...oh wells.
Re: Trajectory B/C
Posted: January 27th, 2010, 10:08 am
by zyzzyva980
I don't know about division C rules, but I'm not sure if battery starts are allowed. Since batteries produce electricity and electrical devices are not allowed (at least in B) then I don't think battery starts would be allowed.
Re: Trajectory B/C
Posted: January 27th, 2010, 12:15 pm
by Balsa Man
zyzzyva98 wrote:I don't know about division C rules, but I'm not sure if battery starts are allowed. Since batteries produce electricity and electrical devices are not allowed (at least in B) then I don't think battery starts would be allowed.
In C they are.
Rule 3.c. "battery triggered devices are allowed...."
starpug wrote:Still does anyone have any ideas/ever attempted battery start. I
Think solenoid.
We have a solenoid pulling up one end of the trigger piece/arm. Ballista, using the old, make that olde, medieval crossbow rolling block trigger design (google to see what it looks like). Works beatuifully.
Re: Trajectory B/C
Posted: January 27th, 2010, 1:03 pm
by andrewwski
I don't see anywhere in the B or C specs where electronics are prohibited, and line 3c permits battery trigger devices in both divisions.
Re: Trajectory B/C
Posted: January 27th, 2010, 2:10 pm
by zyzzyva980
I'm not sure. I'm just remembering that from the last time I read the rules. I think battery-powered devices might be allowed in B as well, but I'm not sure. You already know I'm biased against lasers, and battery power is in the same family.
Re: Trajectory B/C
Posted: January 27th, 2010, 3:28 pm
by andrewwski
I have both copies of the rules in front of me (and they're exactly the same for both divisions, as they list both divisions' specs in both the B and C rulebook), and it definitely allows for battery triggers. And I don't see anywhere where electronics are prohibited (other than to supply the launching force).
