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Registered Member #61926
Joined: Wed Nov 22 2017, 04:08PM
Location:
Posts: 34
I finished my first prototype gauss cannon that contains a microprocessor to control the power supply to the coil, and a phototransistor light-barrier to determine the time for deactivating the magnet. The design is very simple and faulty, but I hope to be able to improve and expand it in the future.
The construction consists of an ESP32, one working light-barrier (another one is not connected yet), a 1mm-wire spool (4 cm outer diameter, 1.4 cm length) that is wound on an acrylic tube (1.2 and 1.0 cm diameter). As a switch I am using a MOSFET (IRFP 2907, 75V, 209A), triggered by a MOSFET driver. The projectile is cut from of a steel nail (0.95 x 3.5 cm) and has a weight of 18g. Power is delivered by a capacitor specified with 50V, 15mF, that is only charged up to 40V at the moment.
The next steps will be to enhance the wiring, set it up to measure the projectile's speed, test bigger capacitors and increase the voltage. In the future I also would like to add more stages and see how it goes...
edit: I soldered shorter wires to the capacitor which resulted in an extremely fast projectile - the light-barrier was reached in about half the time. I also tested a 22 mF capacitor and combining the 15 and the 22 mF capacitor, resulting in a slightly shorter passing time.
Registered Member #61926
Joined: Wed Nov 22 2017, 04:08PM
Location:
Posts: 34
My plan is to go near 100 V and use multiple coils with 1mm-wire, 9 rows and 10 layers. The first shots utilized only 40 V because I did not have a fitting step-up converter then (still I do not have 100V-capacitors, so I will not put the plan into practice soon).
The current version is much more powerful than the one on the last video. I did attach the second light barrier, so the display shows the speed and the energy after each shot. Also the wiring at the coil is much better. Yesterday I shot a 128g-nail (because I cannot find the small projectile anymore), which was measured at 0.88 joule at about 40V. Today I connected another step-up converter and went up to 46 V with a new 20g-projectile, which resulted in a speed of about 9.9 m/s and 0.98 joule (if my math is correct).
Now I need to design something to catch the projectiles safely
When I click you first link @V2006, I am forwarded to a page asking for my youtube-login data, but I do not see any video. I noticed that before, as I watched your videos in the past.
Registered Member #61926
Joined: Wed Nov 22 2017, 04:08PM
Location:
Posts: 34
I will think about the wire size, what kind of wire are you using? I remember reading somewhere in this forum, that wire above 1mm would be almost impossible to roll up properly, so that might have been the reason why I chose this diameter.
However that may be, here is another video I just made. At the end there is also an old shot, that I made about one day ago.
Registered Member #62267
Joined: Sun Apr 29 2018, 10:28AM
Location: Brno Czech Republic
Posts: 2
Hi, I like how your project is made modular but I would recommend you to make all the power wires as short as possible especially that mosfet connection. Also you might achieve better results with coil with the same length as the projectile and place that light barrier on the other end of coil and switch it off when projectile reaches it. I would also like to ask where did you buy the acrylic tube? Anyway I'm looking forward to new updates.
Registered Member #61926
Joined: Wed Nov 22 2017, 04:08PM
Location:
Posts: 34
I will make the wires shorter in the next versions, this is not meant to be highly efficient, yet.
Tomspol wrote ...
Also you might achieve better results with coil with the same length as the projectile and place that light barrier on the other end of coil and switch it off when projectile reaches it. I would also like to ask where did you buy the acrylic tube? Anyway I'm looking forward to new updates.
Why should the coil be the same length as the projectile? Could you give me a hint towards the pysics behind it? I was thinking about using a much longer, heavier projectile, to be able to transfer more energy because of longer influence of the magnetic fields, especially in the later coils. I read, that the best results would be achieved when the length and diameter of the coil would roughly be identical; If you double the length of a coil, the magnetic field strength is halved (provided the length of the wire stays the same), right? In case there are no/few experiments on that matter, I might try to build two coils with different length/diameter-ratios and test the resulting speeds... but I assume that the analysis will be tricky, when also bringing the energy consumption into accout.
When calculating coils with a thicker wire I had the impression that (striving for the same amperage as a thinner-wired coil) the time for the magnetic field to strengthen would be much longer. When comparing a 1mm to a 1.9mm wired coil, the time to reach 90% of the maximum current rises from 3.8 ms to 21 ms. Also the time for the current to go to zero after deactivating the coil should be much longer, so in conclusion the coil would have to be activated earlier and deactivated some time before the projectile reaches it's center, to prevent retardation after exceeding the center? I am not sure if the results of my calculator are dependable, and my physical knowledge might be not sufficient to interpret it correctly, but I have the feeling that the advantages and disadvantages of different sizes of wires about even themselves out (with much higher costs and weight when using thick wires).
What do you mean by placing the light barrier on the other side of the coil? So that the projectile interrupts the light before reaching the coil (to get reproducable starting positions?)? At the moment, the projectile is placed before the coil manually, and the magnet is turned off when the projectile reaches the first light barrier behind the coil. The second coil is only for measuring the speed.
Maybe it would be the best to start from scratch (apart from the wooden wall), because there are so many thing I would like to change. Then I would do a much more stable mount for the unmeant moving parts, that would allow adjusting the distances of the components easily; meter the voltage of the capacitors by the ESP32, so the energy consumption after each shot could be displayed, and so on...
I bought the tube in a german shop "Holzmaus" (=Wood/lumber mouse) that has a large variety of tubes (but also other materials and forms): They only deliver to Germoney, Austria, the Netherlands, Luxembourg and Belgium.
Registered Member #62267
Joined: Sun Apr 29 2018, 10:28AM
Location: Brno Czech Republic
Posts: 2
I'm sorry, I didn't write it right. I meant placing light barrier on the beginning of the coil such that when you load the projectile into coil the light beam is interrupted. When you fire the projectile starts moving and when its whole in the coil (if the projectile has same length as coil) it clears the light barrier and coil is switched off. It looked like if you have the light barrier behind the coil the projectile is being pulled back before it reaches the light barrier. But on second thought it pretty much depends on length of projectile.
From my experiments I've got the impression that identical length of coil an projectile would be better than coil with large diameter and longer projectile. But I might be mistaken, it would definitely deserve more look into.
I'm not quite sure what do you want to achieve by increasing wire diameter. You could increase current through coil just by using higher voltage.
Registered Member #61926
Joined: Wed Nov 22 2017, 04:08PM
Location:
Posts: 34
Tomspol wrote ...
I'm sorry, I didn't write it right. I meant placing light barrier on the beginning of the coil such that when you load the projectile into coil the light beam is interrupted. When you fire the projectile starts moving and when its whole in the coil (if the projectile has same length as coil) it clears the light barrier and coil is switched off. It looked like if you have the light barrier behind the coil the projectile is being pulled back before it reaches the light barrier. But on second thought it pretty much depends on length of projectile.
From my experiments I've got the impression that identical length of coil an projectile would be better than coil with large diameter and longer projectile. But I might be mistaken, it would definitely deserve more look into.
I'm not quite sure what do you want to achieve by increasing wire diameter. You could increase current through coil just by using higher voltage.
You are right about the placement of the light barrier, another advantage would be that the triggering might be more exact, when using a projectile that has a flat back, but a pointy tip. I already thought about that and might change my design in the future. At the moment I am not sure, how to shape the projectile, if it needs fletchings, like a arrow, to get a stable flight... so far, my idea is to hollow out the rear part of the nail to make it lighter than the front.
The increased wire-diameter was a thought based on V2006's reply directly above yours. I think the reason behind it would be to increase the magnetic field strength and the amperage, or the length of the coil to have a longer time of energy transfer. Using a higher voltage would also lead to changing many other parts, like MOSFETs and capacitors, so I think I will stay at 1mm for now.
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Yet another coil gun prototype
