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Makes a lot of sense, since you want the length, where dB/dx is large to be big, not the length inside the coil, where B is almost constant. Depends somewhat on whether this is the first stage or a later one. Also, the L/R ratio, which describes the length of time, which the field takes to die down, is roughly proportional to the copper cross section of the coil, i.e. the area of copper you see, when you saw through the coil perpendicular through its axis. If you want that to be large, you end up with short fat coils.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
From memory, the length should equal the inner diameter, and the outer diameter should be three times the length, so that when you saw through it, the two sections of coil that you see are square.
If I get a chance, I'll try to find some references. There's a name for this shape coil, but I don't remember that either.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
DerAlbi wrote ...
actually yes. without saturation, the force increases quadratically with current, with saturation it rises only linear. Of course resistive losses rise by square-law..so you want the force to rise the same way... and with saturation you dont have that.
Its all a tradeoff... if you want to be a cool kid that shoots stuff on youtube that shatters easily anyway then you want maximize outputpower... in a basic design this leads to bad efficiency. I f you want to be cool on the number-side,you wont be recognized for it, but you will win efficiency
Yup, but at high speed this no longer applies so much because resistive losses are small compared to the mechanical power you're generating, so you have to be careful with the first few stages and save energy for the later ones. On the later ones you can go further beyond saturation without a lot of penalty, within reason, and reducing the number of stages you need.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
Ash Small wrote ...
From memory, the length should equal the inner diameter, and the outer diameter should be three times the length, so that when you saw through it, the two sections of coil that you see are square.
If I get a chance, I'll try to find some references. There's a name for this shape coil, but I don't remember that either.
Please let me know if you find any references--or have any clues where to search for such pertaining to single-stage. I have looked but can't find any like this. I see why this one would be for multi-stage only...If you plan to launch a 1/4" projectile from one stage with these guidelines, the coil's dimensions would be quite unusual: OD=3/4" ID=1/4" AND Length=1/4" ! Am I correctly interpreting this? If you had the OD vs the LENGTH rule backward this would become: LENGTH=3*OD. Which looks like better dimensions for a single-stage coil.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I think what you suggest is impractical, although you may correct me.
If the coil ID is 1/4", the OD of the barrel is 1/4", this sounds impractical to me, although you may have a specific application in mind.
If the projectile is 1/4" diameter, and wall thickness is 1/16", then you have 3/8" ID for the coil, this still sounds a bit on the small side to me.
I was visualising something like a half inch bore ID, 1/4" wall thinkness, coil of 1 inch ID, 3 inch OD and 1 inch long, although this can be varied a bit, as long as the proportions remain constant.
This will only work for a multi-stage coil gun.
Maybe you coul go to 1/4" projectile diameter, 1/8" wall thickness, 1.5" coil OD and 1/2" coil length.
What I mean is if the coil is as long as it is high (ie square cross section), this seems to be very efficient for lots of applications, not just coil guns.
This is just something which has 'gelled' in my mind from reading lots of posts on this forum. It also seems to be efficient for other types of coils, as well as coil guns.
I'm sure there is a name for this 'coil topology', but the name currently escapes my memory.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
Ash Small wrote ...
I think what you suggest is impractical, although you may correct me.
If the coil ID is 1/4", the OD of the barrel is 1/4", this sounds impractical to me, although you may have a specific application in mind.
I think we are misunderstanding each other here: From what you originally stated. You said:
"THE LENGTH SHOULD EQUAL THE INNER DIAMETER, AND THE OUTER DIAMETER SHOULD BE THREE TIMES THE LENGTH"
From this I get, using as an example, a 1/4" diameter projectile, the following: Coil ID=1/4" Coil OD=3/4" and coil length=1/4"??? I am assuming:...the coil ID = the barrel OD. And very thin walls, therefore, coil ID~projectile diameter (1/4"). This is what I found odd for a coil.
PLEASE correct me if I am misinterpreting the the above assumption (written in all caps).
EDIT: I re-read your last reply and saw that you were not ignoring "VERY THIN" wall thickness--I was--when I am able to reply without double-posting, I think we will be in understanding.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I found a link to a thread from two years ago, started by Yanderson, who hasn't posed here for some time, but he did do quite a bit of exermentation regarding coil efficiency.
You can see the dimensions of his coil fit exactly the ratios I described.
I seem to remember there was another thread here he discussed why he felt that this was the optimum shape for a multi-stage coilgun coil.
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Coil length
