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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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This was the final schematic for the device and I used a switch like on the picture. Because the switch has only 4 mm between ON-OFF position it was easiest to use a thread which was broken after the switch activation. I put the thread with double loop.
 

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This device, with a slide switch, has one flaw that increases the measurement error. The problem is "bouncing" of the contact. I found that the duration of this bouncing could be about 0.1 ms. If we increase the measured time (dt) by 0.1 ms the result could be better.
If we increase a time of 5.1 ms to 5.2 ms the speed would be 32.6 m/s which is almost as calculation values ​​(error 1.8%).
 
Now that I know the speedometer works, I improved the switch activation.
[ame=http://www.youtube.com/watch?v=FgsS4HzkUP8]YouTube - ‪Actuator‬‏[/ame]
 
Here are the results of speed measurement in sea.
Tomba plastic slider and mono 1 mm was used with the gun on 25 bar.
Dependence of speed to distance is very similar to exponential function.
For the tip of the shaft the distance is actually for the shaft length longer, for the same speed.
 

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the regard tromik!
Good work...
I seem that results were got uprated...
Possible check the results of the measurements to energy on distances 4 metres, on fact...
 
Vlanik said:
the regard tromik!
Good work...
I seem that results were got uprated...
Possible check the results of the measurements to energy on distances 4 metres, on fact...
Click to expand...

You could now compare this results of measurement to your calculated data.
Cheers, Tomislav
 
I have already compared...
So and offer you to conduct check...
The Single variant is grapped, this check real and accounting енергии, method of the depth пробивания test dartboard...
 
I was using two different systems for measuring the speed end energy of the shaft. The second one, with a surgical rubber tubing I was using before alone to compare performance vacuum barrel to water barrel.
[ame=http://www.youtube.com/watch?v=eV40ikyfWpY]‪Mjerenje‬‏ - YouTube[/ame]
 
I made a few measurements with Cyrano1100 on 22 bar, too. Tomba slider, 1 mm mono, 1290/6.5 mm two barb shaft, 0.375 kg.

From the starting speed vo = 35 m/s and a speed on Lo = 5.71 mm (3 wraps of mono) v1 = 6.8 m/s, because I know the dependence of speed (v) to distance (x) is exponential this is a function for the speed:

v = 35e-0.287x [m/s]

The calculated speed is actually the speed of shaft tip on distance x + 1.29 m.

I wanted to make some measurement more but my DVM had become wet :vangry.
Water entered the plastic bag with DVM and batteries.


For Cyrano850 on 25 bar 1003/7 mm shaft (0.334 kg), 1,5 mm mono, Tomba plastic slider, vo = 33 m/s, on distance Lo = 4.17 m, v1 = 8.5 m/s. Function for speed is:

v = 33e-0.328x [m/s]

The calculated speed is actually the speed of shaft tip on distance x + 1.003 m.

Vlanik, I made this functions for you.
 
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tromic said:
Vlanik, I made this functions for you.
Click to expand...
Thank you!
Beside us very close results...
As soon as will appear the possibility, I shall remove the features to energy of the harpoon on distances...
Possible this I understate ballistic given in its xls...
 
Fantastic but how are these figures comparing to a same length band gun?
 
foxfish said:
Fantastic but how are these figures comparing to a same length band gun?
Click to expand...

I do not know yet, but I suppose it should be better than band guns of same length. I just made a calculation for Cyrano 1100 and 6,5 mm shaft, 1 mm mono, tomba slider. On 26 bar and 6 m distance the speed of the shaft tip should be 9,9 m/s and energy about 18,3 J. Starting speed about 38.5 m/s. Quite good!
 
Reactions: Don Paul
Vlanik said:
This bad...
Too high starting velocity...
Much losses...
Needs the harpoon by more diameter...
Click to expand...

Good for 6,5 mm shaft, but 7 mm or 8 mm would have less losses on the way to the target distance because of possible lower starting speed.
 
Vlanik said:
This bad...
Too high starting velocity...
Much losses...
Needs the harpoon by more diameter...
Click to expand...

Depends on the circumstances - if you are hunting 2kg fish at 2mt range the spear will go right through the fish & then it is very difficult for the fish to escape. I like fast thin spears for close range fishing

It seems most guns that work out of the water are measured in "foot pounds" of energy. [ame="http://en.wikipedia.org/wiki/Muzzle_energy"]Muzzle energy - Wikipedia, the free encyclopedia[/ame]
 
tromic said:
That diagram is just example how the voltage change with speed.
I use a formula to calculate time:

dt = ln(U0/U1)*R*C

and than the speed is

v = dL/dt (m/s)

In my case dL was 0.178 m
Click to expand...
Thank you, I so-so and presented that this dependence was calculation description...
This dependence of Exp... what level does dV undertake on dt ?
 
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