Catapult Trigger: Creative Ideas for Pulling String

[Coco12]

Does anyone have any cool ideas for a catapult trigger. I plan to have a hook attached to bottom of cup that holds the ball and 2 hooks on the base that when you pull the catapult all the way down and put a nail through all three hooks. There will be a string attached to the nail but I need something that would pull the string and the nail along with it.

 

[Myslius]

Step 1 (optional) Get a dog
Step 2: Train your dog to do fetch command
Step 3: Attach the string to the dog's tail and do the fetch command
And... that's how you do remote controller.

 

[NascentOxygen]

A slot-car motor could wind the string around a pulley or shaft.

 

[Enigman]

A trigger complicates thing a bit too much as far as a catapult is concerned...
But even so, here is something I had thought of doing:
(With a trebuchet - 5th grade sci. project...never completed the trigger part)
A Large spur gear fixed to the 'projecting shaft' synced to another gear (a spur gear cut to get 120 deg section) attached to a (4.5V I think) DC motor controlled by a switch.
The motor gets the shaft down- switch off- Lock and load- Switch on again- as the gears lose contact the projectile launches-gears regain contact- cycle continues.
But I never tried it out...no spur gears of the required sizes and cutting up beyblade rip-cords wasn't exactly working out...project was due soon too...

 

[Coco12]

The trigger must be small in size can't be too big, and must be made with materials from home( easy to get and doesn't cost much)

 

[Coco12]

For example anything I could do with magnets?

 

[Enigman]

For example anything I could do with magnets?

Permanent magnets won't help but electromagnets might but a mechanical solution is the best IMO.
How much automation do you want? If you are okay with manually dragging down the shaft and just are looking for a trigger you could just use things like board clips/clothespin and a piece of string for a simple solution. Or if you are looking for something more elegant you could use a string and pulley (a bobbin or a reel would do nicely) attached to a handle which can spun to bring the shaft down and released to fire.

 

[berkeman]

Does anyone have any cool ideas for a catapult trigger. I plan to have a hook attached to bottom of cup that holds the ball and 2 hooks on the base that when you pull the catapult all the way down and put a nail through all three hooks. There will be a string attached to the nail but I need something that would pull the string and the nail along with it.

Since this is likely a schoolwork project, I will move the thread to the Homework Help forums, and only give a visual hint...

http://www.doorware.com/images/products/deltana-mortise-bolt.jpg