[Punchanello]

Hello!
I'm trying to enter a physics contest with my college and it is based on launching a junior baseball ("t-ball" 145g and aprox 5.7cm diameter).
I have to be able to transport it so I am considering using a design similar to the bullpup slingshot with the bands wrapping around pulleys to increase draw length.
I was trying to use the theraband calculator and estimated the weight is similar to a 35mm steel ball, but the ball I'm launching is much larger. I want max power, because there is a distance component to the contest as well as accuracy. I was wondering if there is a standard ratio for the taper used to increase power, and if I need to increase the band width or length to launch a larger diameter ball?
My team and I are trying to reach 150 meters for the launch distance.

I appreciate any and all help,
Punch

 

[JohnKrakatoa]

hmmm, sounds nice.

Basically the bigger the taper the faster the projectile and the lower the band life. 150 meters shouldnt be a problem. In fact I think that if you are a strong fellow you could shoot that baseball out of a normal slingshot with some heavy tapered and heavy bandset of TBG.

 

[TheDaddy187]

[ame]https://www.youtube.com/watch?v=Om0O0_gr6Vo[/ame]

 

[fred45]

well

that should do it.

 

[Punchanello]

Thanks for the input everyone. I've been going back over the videos Joerg has posted and taking into account the physics of the bands. What I'm wondering now is,
What is a safe elongation for TBG? I'm trying to figure out what a relatively safe amount of stretch is to maximize power. I'm trying to determine with the TBG I have how long I can make my launcher to achieve maximum acceleration time.

Also, I found a chart relating the pounds of resistance for TBG at different percent (%) stretch, and wanted to verify that it reads as simply as it looks. Example being, is 200% simply stretching a 12inch band to 24 inches?

Thanks again for all the help!

 

[lucas414]

Why do i never have to do something like this for school, finaly something i would get an a for

 

[papalasher]

You may wish to consider a dry ice or similar source of gas with a quick release valve for potatoe gun style launcher, it could potentially out perform the TBG.
As for maximum stretch, theraband say on their website that it'll break at approximately 4 times it's relaxed length.

 

[Punchanello]

No canons allowed. No water pressure, gravity engines, etc... Thanks for the idea though.

 

[Punchanello]

Building of the unit starts tomorrow so I'll be sure to take photos.

 

[Punchanello]

Ok, working on getting the pictures to my computer so I can get them posted here.
In the mean time I was wondering, We're attaching the bands at the front with carabiners and the bands get all bunched up.
Is having the full width of tapered bands spread out on the front of the slingshot related to it's power?

Is there an effective way to use rings or carabiners to attach the front of the bands?

Our initial shot of the ball went about 45 meters with one set of bands (one strap each side). I used TBG 12" long and tapered from 3.25" to 1.75". I think if we increase the number of bands we can get to 150m but I want to optimize the design to ensure we're getting most power out of each band.

Thanks again for all the help!
Punch

 

[Courier]

Maybe you'll find this video by Joerg interesting too.
<iframe width="560" height="315" src="https://www.youtube.com/embed/aGsK86TkLhE" frameborder="0" allowfullscreen></iframe>

 

[Punchanello]

https://youtu.be/Ffa9ndPZFRM

Ok, here's the first test of our rig. I'll do an actual video for it after we get it finished. It is strapped to a ladder for the base, and is using the bullpup design that Joerg used in his "bullpup crossbow slingshot". I'm still working on getting the friction reduced on the rollers, currently they're binding up and reducing the full flex of the bands. The first launch achieved a distance of roughly 45 meters.
These are tapered bands, but I was looking at some of Joerg's videos and I'm thinking of using untapered for the actual contest since we'll have to fire it multiple times. It looks like he uses bands that only really tie at the front? Like flat bands wrapped through the pouch and back to the front attachment on his rigs.

Biggest question. Is there a method, or any specific cautions agains tying the front of the bands to carabiners for easy changing? Should I avoid using clips for the front of the bands? Does that change the band's power?

 

[TheDaddy187]

i cant see any problems with using carabinas provided they arent the cheap tacky ones that break too easily...

maybe the bands would wear out faster if they hit any edges on the carabinas, but other than that i cant see problems...

a suggestion, make your shooter longer... if it was twice the length then the ball would be accellerated for twice the distance and will give much more distance to the ball

 

[Punchanello]

Thanks for the suggestions. Due to space for transporting I couldn't make the unit longer. We did the competition today, and won! Our long distance shot went off the field and was estimated at our goal of 150m.

I have some videos from the event but they aren't very good
https://youtu.be/dIKrUCWiMXs?list=PLktFjlocKp44cqMiTc1VgWs0wTLf4fkjZ

https://www.youtube.com/playlist?list=PLktFjlocKp44cqMiTc1VgWs0wTLf4fkjZ

I will try to get a better video in the next few weeks after finals are done at school. Just need to rebuild the trigger since it broke during our long distance shot. Joerg is right Plywood would have worked much better than the 1x2 pine I used.

 

[JoergS]

Congrats! Winning is just great. Well done.

 

[bigdh2000]

Sweet win.

More video! More video! More video!

...we always like more video.

 

[GunGuy]

Very nice, congrats on the win. If you have any pictures or video of the competition I wold love to see that too.

 

[Punchanello]

Unfortunately I haven't been able to track down other photos and my team camera guy was focused on us. The team next to us built a Joerg design too. The built something similar to the Smaug killer but for a ball. They used surgical tubes instead of Thera band. That's probably the only reason we won instead of tied