0
$\begingroup$

My middle schooler is building a catapult that’s supposed to hurl a ping-pong ball 5 meters:

enter image description here

The problem is that the pressure on the latch is so high that the kid just cannot trigger it:

enter image description here

The door latch used as a trigger is being under so much pressure that it just wouldn’t slide out. I doubt that adding lubricant would help enough.

Thus the question: what latch design could you suggest so that it would operate smoothly under lateral pressure?

$\endgroup$
  • 2
    $\begingroup$ Have a look at this resource: Alexander Slocum's wonderful guide to making stuff. Page 19 of this pdf shows you how to make a trigger. web.mit.edu/2.75/fundamentals/FUNdaMENTALs%20Book%20pdf/… $\endgroup$ – D Duck Mar 8 '19 at 9:27
  • $\begingroup$ I would recommend keeping that bolt as a "safety" and adding one of the designs in the answers as the actual trigger. $\endgroup$ – Carl Witthoft Mar 8 '19 at 16:49
  • $\begingroup$ @DDuck, this is exactly what I wanted. Thanks. $\endgroup$ – Michael Mar 8 '19 at 17:34
5
$\begingroup$

How about a levered latch like this (very rough sketch) showing the catching tooth above the self latching spring and the pivot point.

enter image description here

| improve this answer | |
$\endgroup$
  • $\begingroup$ Thanks! Could you you suggest places where I can get a piece like that? I don't see pieces of this form at Home Depot. $\endgroup$ – Michael Mar 10 '19 at 17:57
  • $\begingroup$ They surely have a 3 inch angle bracket or corner bracket (often used for cheap doors or boxes) which you could cut and drill as necessary... $\endgroup$ – Solar Mike Mar 10 '19 at 18:11
2
$\begingroup$

My son made a model trebuchet which is a sort of medieval catapult. The trigger mechanism is quite simple using three screw eyes and a pin. In case the picture below isn't clear, the there are two screw eyes attached to the frame and a single screw eye attached to the arm with a pin through all three screw eyes. Attaching a string to the pin keeps hands away from things when launching.

enter image description here

| improve this answer | |
$\endgroup$
1
$\begingroup$

Consider to replace the latch socket with a pin. The pin extends from the side of the moving part.

Pin A is held down by a smaller version of the catapult platform, with a hinge at the opposite end. It also has a pin (B) which is held down by another small hinged lever. When the device is unloaded all the hinged portions are held upright out of the way.

The catapult platform is pushed into position and the first lever drops over the pin. The second lever drops over the first lever's pin. The latch holds the second lever down, with a substantial reduction of force.

This is a derivation of the three-ring release designed, patented and produced by Bill Booth and is created in various ways for similar purposes.

force reduction image

Keeping the hinges close to the pin improves the force reduction for each stage.

| improve this answer | |
$\endgroup$
0
$\begingroup$

With caution and your supervision:

He can use a mouse trap spring and release mechanism. They are efficient and easily release, but require caution handling.

| improve this answer | |
$\endgroup$
  • $\begingroup$ Well, if you reconfigure the mousetrap so it doesn't snap metal towards the trigger, one problem solved. The other thing, since it's a very sensitive trigger, is to have a "safety" on the main catapult assembly. $\endgroup$ – Carl Witthoft Mar 8 '19 at 16:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.