Speargun muzzle velocity

    I don't really care about the speed with which the spear leaves the speargun as a number but I thought the following was brilliant.

    Quote from wkitto

    Put a cheap microphone into a condom --- tie it off so the mic doesnt get water in it. Connect the mic to a laptop and put it (the mic since you still may not be thinking) into a pool where the gun will be shot at a wooden target suspended off the bottom by strings to your weight belt. Accurately adjust the distance from the end of the shaft to the target (15 to 20 ft for example) and with the computer recording shoot. Review the digital image of the sound in a sound editing program to measure the time distance from the sound of the mechanism and bands going off to the impact of the shaft at the target. From that point with a little engineering help you ought to be able to figure the average velocity over the distance traveled.


    kitto
    http://IC_Spearguns.tripod.com

    I actually thought it was unnecessarily complicated. Couldn't you just film the shot from above, isolate two video frames where the spear is in motion, and count the number of pool tiles traversed? If you know the camera captures, say, 16, or 24, or whatever, frames per second, and you know the length of the pool tiles, then calculating velocity is easy.

    Not at all complicated, it may seem that way if you've never used sound editor software. This program is WaveEditor. It comes included with Nero burning suite so most people have it and don't even know it. I'm sure there's free sound editor software that represents data in a similar way. You can see from the pic that the peaks are where the sound level goes up. In a speargun shot recording you'd see mostly a flat line beginning and ending with a noise spike/peak. You can easily select a portion of the graphical representation and the time appears on the bottom where I circled. You can also zoom into the graph, where half a second would take up the whole screen. This enables you to select precisely where you want to know the time.


    To make the whole thing even less complicated I could use my digital camera with its underwater housing to make a video recording which includes sound. This can be done while actually shooting a fish in open water. The sound data from the video can easily be treated in the same way.


    Quote from seahunter49

    I don't really care about the speed with which the spear leaves the speargun as a number but I thought the following was brilliant.


    I guess Mr Kitto has too much spare time and creativity to find engeneering uses for the condoms and Mics :pot5:


    Brilliant idea Anyways

    I'm a Speardiver, not a freediver

    I'm a BSEE btw, but I also manufacture pole spears and spear tips along with lots of other parts.


    I see the need to make an underwater chronograph for my own use in testing design features etc.


    I think I can come up with something that could handle the water and measure muzzle velocity along with impact speed.


    With the programmable PIC chips out there, the electronic aspects are not so hard. It's all about getting a good trig pulse for timers. I've worked with Optics for many years and have many resources, so I'm sure I can come up with a robust detector system.


    With the PIC chips and associated products you can collect the data and also do downloads to computer with not much effort.


    I did not want to re-invent the wheel if there is something already done. Anything on the Market?


    Be a fun project, but got lots of other stuff to do.


    -John

    Agree, and it's not a hard project with the technology of today. Pic chips are like dirt cheap, under $5 each and easy to program. Each Chip is like it's own computer. Low power draw, and could use rechargeable batteries, use inductive recharger.


    Hermetically sealed parts for water is simple too.


    Still don't know why there isn't a product.


    If I had them, how many divers would want one?


    Maybe I will make 2 of them. One for me and the Other for a one time auction on Ebay starting at $1. and see where it goes.

    "Still don't know why there isn't a product.
    If I had them, how many divers would want one?
    Linghunt---I would buy one from you (depending on the cost of course).


    We have used "low speed chronographs" for years in archery to measure arrow speed. I would guess that arrow speed and spear speed could both be measured by the same type of chronographs. You can buy one for less than $100. here; Search results for: 'chronographs'


    Hope this helps

    SPEARFISHING and RECREATIONAL FISHING NEEDS THE NRA
    Spearfishing Store

    Edited once, last by hau ().

    Just a little different with Water media vs Air.


    Some of them use visible light other use IR for the detector stage. There's a couple ways to skin that cat from what I'm thinking, but going to have coffee with some techy buds next week to ring out easiest, cheapest way to go on this one along with some other projects.


    Range would be slow, say ( 1/2 ft / sec to maybe 100 ft / sec ) that should cover everything we shoot in poles and guns...


    Hau, in reference to the Archery Versions, do you like the bells and whistles of calculating averages and SD's etc. I was thinking of doing all that after download to PC. and only display last shot speed.


    Maybe an on/off button, reset, and a display. Data storage could have raw data with time stamp.

    Quote from Linghunt


    Hau, in reference to the Archery Versions, do you like the bells and whistles of calculating averages and SD's etc. I was thinking of doing all that after download to PC. and only display last shot speed.


    Maybe an on/off button, reset, and a display. Data storage could have raw data with time stamp.


    I need no bells and whistles, just consistently accurate last shot speed for my applications. "On/off, reset and display" would be perfect for me. :D
    Thanks

    Sounds good, What is the longest shoot one would want to take?


    Display would show Initial and Final velocities. I guess I could display the time to travel the distance, but operator would need to measure out the distances from sensor arrays.


    I'm thinking 4 - 6 weeks based on current workload, assuming I don't have too many hurdles.

    Quote from Linghunt

    Sounds good, What is the longest shoot one would want to take?


    Display would show Initial and Final velocities. I guess I could display the time to travel the distance, but operator would need to measure out the distances from sensor arrays.


    1. The longest shot I could conceive taking would be 25-30feet, with most shots considerably shorter.
    2. Initial and (IMO)"Final velocities" information would be a huge asset in building and designing spearguns and spears. Some spearos and spearing applications (Mediterranean) require faster/flatter shooting spears, while some spearos and spearing applications (pelagics) require heavier spears to ensure correct penetration in larger fish.
    IMO,With accurate spear speed measurement:
    1. A gun designer could test one manufacture of gun band against another,
    2. A spearo could use spear speed to calculate spear trajectory.
    3. Spear speed and weight could be used to calculate kinetic energy delivered at X distance.
    4. Spear speed could be used in speargun design and efficiency.
    There are many more.


    Agree 100%,


    I see this item as a tool for evaluating my own designs mostly. I don't see a big market where diver would really want this.


    As for the Big boys, making Guns and Pole spears, I'm sure they already have their designs completely tested for this kind of basic stuff. Couldn't give it away to them, vs. thinking of selling it.


    Making one or a couple of these is about the same. Not sure If I want to make more than that and store in the basement.


    Not sure I want to test gear for folks either and Play "Consumer Reports" , planning tests and other factors is important as having some data tools.

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