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Measuring speed of the shaft

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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An interesting question would be whether the velocity cross-over point occurs for 7 mm and 8 mm diameter shafts at the exact same velocity regardless of the speed that the shafts were fired at initially. For a more powerful gun with a higher muzzle velocity capability than the band gun used by Niko in his tests this would then push the cross-over point further out from the gun muzzle if that was always the case. If line drag determines the velocity cross-over point then this velocity (where v = V, with v for the 7 mm and V for the 8 mm) may change position along the flight path with different line types. Similarly the energy cross-over point, which occurs earlier than the velocity cross-over, may shift position along the flight path with line type changes, or the magnitude of the respective spear muzzle velocities if this also has an effect. Food for thought for additional experiments with these two shaft sizes and other shaft sizes in current use!

Why would we be interested? Well if we have the situation where the cross-over points occur beyond the target then slimmer shafts would be our first choice for their velocity and impact, but if the cross-over occurs well before the target then we have a possible shaft selection problem. Flight time to the target is preferably as short as possible for target interception, but if the target is slow moving and on a predictable course, or stationary, then a heavier shaft which may take slightly longer to arrive will cause more damage if M x (V)^2 > m x (v)^2 (the 1/2 in the kinetic energy formula cancels out on each side of the equation). Assuming that the heavier shaft has mass "M" and velocity "V" and the lighter shaft has mass "m" and velocity "v" at the time of impact with the target, then we can say that for the exact same energy stored in both shafts at that position v = V x sqrt(M/m).

More energy can be stored in a longer gun as the propulsion distance is longer and generally the length of the shaft guide or track section determines the minimum length of the shaft, so the only variable is the shaft diameter and possibly the type of speartip. Short pneumatic guns can propel shafts effectively for close range work (say within two metres) without shaft diameter being an issue, so the main interest is in medium to long range shots where we can perhaps reduce gun storage energy and propel slimmer shafts for the same degree of effectiveness in terms of flight time to target and the impact capability.

Slim shafts used to be too easily bent, especially if they were long, but they can now be made from better materials which means that they can be substituted for thicker shafts. From a practical viewpoint you want the shaft to stay in good shape after the fish is finished with it, otherwise you need some spare shafts! Shaft diameter implications and considerations occur at both ends of the shooting operation for muzzle loaded spearguns.
I made same modifications to the speedometer. Now batteries and DVM are above the water surface during measurement.

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Maybe this is better, the water comes out from the side holes as well as from the front end.

the energy and velocity for harpoon 9мм., very greater...
пересчитай through work when charging...

This is not for 9 mm but for 8 mm shaft. I think this might be good because it is based on measurement (Stefano Soriano). It seems to me that calculation results are not very reliable, except in a narrow range about measured results, for interpolation-extrapolation.

These results are for free shaft, without mono line tied to the shaft!

Test balistica subacquea arbalete IDDU II

I am going to make new measurement for 8 mm free shaft, with my new speedometer, similar to that with 7 mm shaft that I had done. But I will measure speed along the trajectory of the shaft on different distances (0 m, 1 m, 2 m, 3 m, ... 5 m, 6 m, 7 m) and will also use mono of 1 mm, 1.5 mm... I suppose the results would be more realistic.
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I finished my new speedometer.

Here is what I recorded when pull the magnet by hand.

The are two pulses from which I can calculate the speed of the shaft. In this case the speed was about 6 m/s because the distance was 0.1018 m and the time 0.0167 sec.
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Speedometer on the picture above I tested so that I activated it using the arrow that I have fired with bow.

Due to the small coil spacing, 10 cm, it is possible to measure the speed with it to some 36 m/s. If each coil would be connected to a stereo channel audio recorder, it could be used for speeds greater than 36 m/s. I have a digital voice recorder but it has no mic input for an external microphone, so I had to record mono, both coils on the same channel. For higher speed the coil spacing should be higher. I think that 15 cm would be sufficient. For the measurement it s best to take the largest spikes. In the picture that are a pair of "A" or a pair of "B". For most accurate readings it is best to take the intersection of the x-axis of the "A" to "B".

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[ame=http://youtu.be/v6tOW06IyAU]Testing speedometer - YouTube[/ame]
What a great speedo.. 122.4 kph or 76.0558 mph.
I see a target with a coil of armature wire and a bi magnet shaft.:D
Great stuff mate.

Cheers. Don
This accelerometer is best to connect to the mic input of computer. The appearance of the signal is more clear. For each coil, there is only negative and positive pulse with no oscillations.

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It looks like this when the I pull the magnet slower than on the previous picture. In this case the speed would be 4,6 m/s (on the upper picture 24,4 m/s).

Here is a modification to speedometer. Stereo recording, each coil to the separate channel. Also it is possible to measure or detect speed (higher or lower) using additional peak detector and digital voltmeter. This second method might be very helpful and has advantage of reading of velocity in time of shooting.


Next is testing ... and measuring the speed of the shaft under water.
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Fascinating stuff - do you prefer an 8mm spear?

6,5 mm spear is much more easier to load and is faster, but also loses speed faster. 8 mm spear has higher range and impact but is more difficult to load. Depends on the fish you are hunting.
I also made a measurement with spear tied with a 1,5 mm nylon, instead of climax 0,92 mm. The starting speed was 2-3 m/s less.
I made some modifications to the speedometer. Now there are two magnets, spaced 20 cm. A steel line of 20 cm is inserted so both nylon lines may stretch for the same amount. I believe with this configuration I could have more precise measurement because only time difference between two magnets passing though the coils is measured.

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