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Comparison of Sliders for Spears
- Thread starterGazz
- Start date
Thread Status: Hello
, There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
It can take a long time to get an up-to-date response or contact with relevant users.
The "straw" is fixed to the main support spider, the cable, which could also be a thin rod like a bicycle wheel spoke, is affixed to the sample holder (with a screw thread?) and the slider being tested sits on the sample holder. So the slider and sample holder can move up and down together and if the cable is a thin rod then a rubber seal could be placed at the bottom of the "straw" to keep water out of the tube, although it could also contain water that did not move into or out of the bore of the "straw". Main problem is the bore of the vertical column, turbulent flow will start at a certain flow rate for that bore size, so you would need to know the Reynolds number for the tubing used for the column.
Here is another line slide/slider: http://www.stcitalia.net/english/x-shot.html
Some thoughts on this line slide shown here.
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Thanks, all details are clear now. It would be nice if I had STC x-runner for test too! I suppose I will make a test soon! The main problem to be solved is how to make sensitive dynamometer. I made (ugly :-( ) a spring from thin wire for guitar.
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Yes, this is a good idea. I had something similar on mind. The only problem might be difficulty in reading because of not steady force. Adjustable counter balance is also important.
Another idea for testing sliders perormance:
I did measurements today using similar set up. But results seems to be not useful! I suppose (tubing ID)/(slider OD) highly affects the measurement results. In my case ID was 25 mm. Would be better if ID was higher. 100 mm might be better but that makes measurement very demanding! Seems that the first set up (water in pan) was much better!
Some numbers:
Mares: 185 g,
Devoto: 75 g,
Tomba 2: 65 g,
Piece of the shaft without sliders on it: 21 g.
....
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I think the diameter of the test tank must be very large to prevent turbulence inside the water column itself which would otherwise swamp the effects of the slider changes on the measurements. Another approach may be to drag the slider through the water on the end of a fishing line, like a lure, but how to measure the very small variation in the drag, the slider being mounted on a section of "shaft" (or a slim cylindrical body)?
That was also my first idea to drag the slider through the water on the end of a fishing line, and the same how to measure question. Another problem would be the changing length (surface friction) of fishing line. Turbulence is also a big issue. After that I came to water in pot idea.
I made a test of sliders on the image to find out shooting performance of each.
I shoot 83 cm long, 7 mm shaft, in water, from speargun with 1 mm mono, 5.5 m far away. The reference was Devoto slider. The best was the old Tomba slider. Number 1.2 means 1.2 x more energy on 5.5 m than Devoto.
I shoot 83 cm long, 7 mm shaft, in water, from speargun with 1 mm mono, 5.5 m far away. The reference was Devoto slider. The best was the old Tomba slider. Number 1.2 means 1.2 x more energy on 5.5 m than Devoto.
Did you do repeat tests or are the results from one shot only for each configuration? Test results usually have some variability, so there is usually a plus or minus on the actual value which means results which look different may be actually the same unless they lie outside the range of variability for each configuration. In other words would a repeat test yield the same ranking of the results for each type?
The newest results are quite different from attempt made here!?
Here the mares slider seemed to be acceptable.
It seems that sliders behavior is different on low and high speed.
http://forums.deeperblue.com/threads/comparison-of-sliders-for-spears.100956/#post-930515
Pete, I did 6 to 8 shooting with each slider and calculated the average of 6 shoots. I suppose results are pretty reliable. I had some problems with the new STC piston that I put in my Cyrano instead of original mares piston.
I suppose the separating force: piston-shaft was not same all the time. I noticed some strange behavior during loading the gun. Spear gun was at 23 bar. I used only the shaft for Cyrano 850, without the harpoon. I wrapped some insulating tape around the shaft tip not to lose the shaft.
Here the mares slider seemed to be acceptable.
It seems that sliders behavior is different on low and high speed.
http://forums.deeperblue.com/threads/comparison-of-sliders-for-spears.100956/#post-930515
Pete, I did 6 to 8 shooting with each slider and calculated the average of 6 shoots. I suppose results are pretty reliable. I had some problems with the new STC piston that I put in my Cyrano instead of original mares piston.
I suppose the separating force: piston-shaft was not same all the time. I noticed some strange behavior during loading the gun. Spear gun was at 23 bar. I used only the shaft for Cyrano 850, without the harpoon. I wrapped some insulating tape around the shaft tip not to lose the shaft.
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Some other results:
I was most surprised by this last result. For front tying the shaft I used 2 mm Kevlar line, and tied it to micro slider as on this image. I recall that once, few years ago I had similar, very surprising result with 1.6 mm spectra with "free shaft".
Result in image is wrong, should be 1.61 and 0.14.
I was most surprised by this last result. For front tying the shaft I used 2 mm Kevlar line, and tied it to micro slider as on this image. I recall that once, few years ago I had similar, very surprising result with 1.6 mm spectra with "free shaft".
Result in image is wrong, should be 1.61 and 0.14.
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Thanks for the Excel spreadsheet! Six shots per test configuration is better than I would have expected as any form of speargun "field testing" involves a lot of time and effort. I note that the "Tomba Inox" was tested with 7 shots due to the higher variability in its results. One way to look at this variability is to calculate the standard deviation of the 6 (or 7) results, although this statistic improves as more results are taken because the figure obtained is only an estimation of the variability of the results about the average value, which is also an estimated value for that particular slider configuration. The Mares line slide/slider certainly performed worse than the others, even allowing for any variability in the results. I note that you squared the ratio to calculate a relative result for each slider with respect to the "Devoto" slider, is there a reason for that? The rubber stretch length is the length "d" in a Force [F] times displacement [d] graph. The area under this graph measures the energy being absorbed by the rubber band to pull the flying shaft to a halt. This graph approximates a right-angled triangle and we are assuming the graph of "F versus d" is the same each time for every shot, the measured variation being in the base length of the triangle (i.e. "d" is on the X-axis and "F" is on the Y-axis). We don't actually measure "F", which changes as "d" changes.
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Yes, Pete I find it more convenient and accurate to measure energy of the shaft instead of speed of the shaft.
The force to stretch the rubber is F = k * d, where d - stretching of the rubber tubing (m)
Work from the force F is W =1/2 * F * d
Work of the decelerating shaft, W is
W = 1/2 * k * d^2 (J)
Work (Energy) ratio R, measured slider on the shaft to reference (r) is
R = (1/2 * k * d1^2) / (1/2 * k * dr^2) = d1^2 / dr^2
R = d1^2 / dr^2
For the best result, the tiny inox slider R was 1.61
For the "free shaft", using 2 mm line, R was only 0.24.
If I were using 1 mm line the result for free shaft might be about 1.2, same as for old type Tomba slider. I measured it few years ago.
Regarding variability of results, the main problem is unexpected behavior of the line connecting the spear gun and the spear, entangling in different ways.
The force to stretch the rubber is F = k * d, where d - stretching of the rubber tubing (m)
Work from the force F is W =1/2 * F * d
Work of the decelerating shaft, W is
W = 1/2 * k * d^2 (J)
Work (Energy) ratio R, measured slider on the shaft to reference (r) is
R = (1/2 * k * d1^2) / (1/2 * k * dr^2) = d1^2 / dr^2
R = d1^2 / dr^2
For the best result, the tiny inox slider R was 1.61
For the "free shaft", using 2 mm line, R was only 0.24.
If I were using 1 mm line the result for free shaft might be about 1.2, same as for old type Tomba slider. I measured it few years ago.
Regarding variability of results, the main problem is unexpected behavior of the line connecting the spear gun and the spear, entangling in different ways.
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I had may old Tomba10 for 7 mm shaft with me, so I did a test for it too:
I also find some errors in previous excel calculation.
For small stainless steel slider the result is 1.61, not 1.44.
For free shaft the best result is 0.24, not 0.21.
I also find some errors in previous excel calculation.
For small stainless steel slider the result is 1.61, not 1.44.
For free shaft the best result is 0.24, not 0.21.
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Order of the testing may also have a bearing on the results as the rubber being stretched may not completely recover after each shot as the test series progresses. So shots made at the start may be different from those made at the end due to this rubber elongation effect. To determine if that is happening a reference set-up needs to be tested throughout a test series, intermingling it with the other tests.