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Thread: Self Activating Trigger/Timer

  1. #1
    Associate Engineer
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    Self Activating Trigger/Timer

    Hello!
    First of all, if this post is in the wrong place please let me know and I apologize for the enormous explanation, I just wanted to make sure my problem is understood.
    To start off, I am trying to create an entirely mechanical dual deployment system for low power model rockets. Dual deployment is when a smaller parachute (called a "drogue") is deployed at the apogee of the rocket instead of the main chute like a normal rocket. The drogue then slows the rocket's descent down slightly, and an on board computer decides when the rocket is nearing the ground. The CPU then fires a charge and deploys the main chute, slowing the rocket down so it does not break when it touches down. The benefits of this system is that the rocket will not drift nearly as much on descent as one large chute deployed at apogee (for obvious reasons). The problem with this is that in order to implement dual deployment in a rocket you need an on board CPU, a charge, lots of electronics, etc. All this stuff takes up a lot of space, which makes it okay for large, high power rockets, but not good for small low power rockets. This is where I come in. I wanted to create an entirely mechanical dual deployment system. By not having any of the electronics in the rocket, I feel the entire system can be small enough to be used in low power rockets. I have some of the system figured out, but I have encountered a serious hitch and need some help. Here's what I have so far:
    1) The drogue will be deployed through a rear ejection system - the motor fires its ejection charge, creating a reactive force pushing the motor mount out the back of the rocket and pulling the drogue along with it
    2) The rocket's nose cone is now pointing downwards because the drogue came out of the back of the rocket
    Here is the part that is the most difficult, I need a way in which a timer of sorts is activated by either the ejection charge or the rocket flipping over, and when the timer is done it releases the nose cone from the body releasing the main chute. I have had some ideas so far:
    1) When the rocket flips over a magnet falls through a copper tube, falling very slowly, and when it reaches the nose cone it pulls metal pins out of the side and releasing the nose cone
    2) A magnet falls through a tube of water, and upon reaching the bottom does the same thing as above
    3) An hourglass
    I need any ideas/mechanisms that you can think of! Any and all ideas are greatly appreciated. The device needs to be as small as possible, with few moving parts to minimize the chance of failure. SIMPLE IS BETTER. If you have any questions or comments please let me know and I will try to get back to you as soon as possible. The device can be made of about any parts, but lighter is better. If you need custom parts for your design, I do have access to a 3D printer but not a CAD/CAM machine. Any help is greatly appreciated.
    Thank you.

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
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    Quote Originally Posted by J107 View Post
    Hello!If you need custom parts for your design, I do have access to a 3D printer but not a CAD/CAM machine. Any help is greatly appreciated.
    Thank you.
    You're asking a lot... I am doubtful that many engineers or designers are going stop what they are doing and engage in this effort.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
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    Yes, I completely understand if you do not want to spend your time with something like this, but any help that you might contribute would be greatly appreciated.

  4. #4
    Technical Fellow jboggs's Avatar
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    There's a difference between free engineering advice and free engineering services.

  5. #5
    Technical Fellow Kelly_Bramble's Avatar
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    Quote Originally Posted by jboggs View Post
    There's a difference between free engineering advice and free engineering services.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  6. #6
    Associate Engineer
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    Yes, I understand, I was able to figure it out myself. Thank you for your time though.

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