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Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
My inductance value is a little bit high because I did not fiddle with the wire sizes to get 320 turns exactly (came out to about 348 turns). It looks like the results are quite similar.. This is good! The peak force is likely to be overestimated in simple models, particularly when the armature nearly fills the coil...it's the average force that is important... Evgenij, how are you solving the problem? My understanding is that FEMM is not too good with time domain problems...
Registered Member #200
Joined: Sat Feb 18 2006, 01:49AM
Location: Pskov, Russia
Posts: 21
WaveRider wrote ... Evgenij, how are you solving the problem? My understanding is that FEMM is not too good with time domain problems...
FEMM has support of LUA-script language. We use a LUA-script for the description of model. By means of a script the FEMM is repeatedly started for fields calculating in every timestep.
And I compiled your program to Windows-PC, and try use it. But your soft show me more high velocity (approx. on 15%) than my real coilgun devices can reach.
We had originally such excess in our calculations too. Now we make greater work for approach of teoretical and experimental results.
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Two simulations. One letting alone the values calculated by the pre-simulation phase (resistance and inductance , forced additional resistance) and the second with forced initial inductance. Same problem as waverider (the last coil layer is incomplete)
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Hhmm, ehm no wave. I'm building the halfbridge and have simulated that some time ago. The first stage is very similar to that we modelled except that there is an igbt instead a scr and it can turn off when the projectile crosses center.
maybe we should construct this device and test the models.
For the halfbridge i obtained energies up to 5.6J and speeds in the 49m/s range (total eff 7.9%), quite disappointing since i dreamed to break the 10J barrier with my halfbridge, i hope that my simulator is wrong .
Anyway throwing toghether this coilgun would be easy. I have tons of 2n6509 25A scrs and tons of 120uF disposable camera caps. I will search if i have the barrel.
EDIT: I found an old barrel from a previous version of the halfbridge. It has holes for the sensors but that's not important. Outer dimension 8mm, inner 6 mm, projectile 5 mm.
Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
Evgenij wrote: FEMM has support of LUA-script language. We use a LUA-script for the description of model. By means of a script the FEMM is repeatedly started for fields calculating in every timestep.
Hmm.. I thought you could do something like this.. What assumptions did you make in terms of saturation model? How did you link the FEM to the circuit model? Your velocity seems a bit low, but the current curve looks good...
And I compiled your program to Windows-PC, and try use it. But your soft show me more high velocity (approx. on 15%) than my real coilgun devices can reach.
[
This is typical behaviour, since the coil winding model is very simple. The FEM will certainly give better results. Also, my simple model is not designed for modeling open coils (although an open coil can be "fudged"...)
We had originally such excess in our calculations too. Now we make greater work for approach of teoretical and experimental results.
My FEM-based model gives far better results for open coils. FEMM should produce good results, too.. Altho' we won't know for sure until we do the experiments!
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Waverider is right, we have no experimental reference to test the data.
Evgenij can you tell me the saturation magnetization of the armature you tested?
I think that in this thread will be more to learn with some experimental data. I need some time to build the test device, I have exam sessions now, so need to study, no time for hand-working. Maybe the next week I will build it
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
I have built a test device to measure speed of a given configuration and set of parameters.
The setup is simple. A single coil with SCR+Diode configuration, 920uF worth of capacitors, the coil, a multimeter, a pushbutton, a rogosky pulse amperometer (my creation)
Cirtuit parameters: Capacitance:920uF Capacitor total ESR : 87mohm SCR voltage drop: 1.4V Diode voltage drop : 800mV
Remaining parameters: Saturation magnetization(steel): 2,0Tesla (this gives the bigger problems) Initial permeability (steel):5000 No shields
Results:
Dryfires: 7 measures, average 302,7A standard deviation 4,4A
projectile fires: Speed:14 measures , average 14,7m/s , standard deviation 0,3m/s current: average 299,3A,standard deviation 2,5A
Differences:
Dryfire simulation: 303,7A (+0,3%) Projectile simulation (current) : 296,6A (-0,9%) projectile simulation (speed) : 18,4m/s (+25%, seems very high, but consider the indetermination on weight, saturation magnetization and position repeteability, also no eddy currents considered)
Simulate and tell me your results for these parameters:
attached there are the excel sheet, and the graphs along setup photos
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Simple mechanical coilgun model
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