Simple mechanical coilgun model / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Simple mechanical coilgun model

first previous 2 3 4 5 next

Move Thread

LAN_403

Evgenij

Wed Mar 01 2006, 12:30AM

Registered Member #200 Joined: Sat Feb 18 2006, 01:49AM
Location: Pskov, Russia
Posts: 21

TheMerovingian wrote ...

a rogosky pulse amperometer (my creation)

Are you sure in linear and precision of this type of current sensor?
I use 3 resistors 0.1 Ohm 5W 1% in parallel and have 33 mOhm current sensor for DSO scope.

TheMerovingian

Wed Mar 01 2006, 01:10AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

wire diameter is 0,8mm , 300Vin , 5.5 mm diameter x 30mm

Evgenij

Wed Mar 01 2006, 03:26AM

Registered Member #200 Joined: Sat Feb 18 2006, 01:49AM
Location: Pskov, Russia
Posts: 21

TheMerovingian wrote ...

wire diameter is 0,8mm , 300Vin , 5.5 mm diameter x 30mm
and
Speed:14 measures , average 14,7m/s , standard deviation 0,3m/s

Then my simulation result 14,44 has standart deviation interval. OK.
But check your current measure system. In this simulation I have 221A peak current only.

WaveRider

Wed Mar 01 2006, 09:05AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

The simple model gives a final speed of 16.5m/s.. Not too bad, given that it is not designed for open coils.

It is difficult to adequately represent open coils in simple models.. The FEM will always be the best way to go.. Evgenij's results seem reasonable to me.. I'll run it through "BigShot" later and see what happens...

TheMerovingian

Wed Mar 01 2006, 10:36AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Evgenij take into account that the coil isn't perfetly fitted. That's i measured the inductance and resistance. Boh RCL simulation an measurements show a current in the 300A range

We need more experimental data.

WaveRider

Wed Mar 01 2006, 08:25PM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

I meant to say that Evgenij's speed calculation was pretty good.. His coil current seems a bit low.. In any case, I will believe the measurements more readily than any simulation!

Cheers!

Evgenij

Thu Mar 02 2006, 03:48AM

Registered Member #200 Joined: Sat Feb 18 2006, 01:49AM
Location: Pskov, Russia
Posts: 21

TheMerovingian wrote ...

Both RCL simulation an measurements show a current in the 300A range

You have mistake in both case.
Do measuring of current as more high accuracy and you will see. When high current going to SCR, common wire, inner capacitors ESR, soldered points e.t.c then voltage drop will high and current low. Are you seriously think about 2n6509 SCR's voltage drop is 1.4V at 200-300 Amps?

TheMerovingian

Thu Mar 02 2006, 07:25PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Evgenij wrote ...

TheMerovingian wrote ...

Both RCL simulation an measurements show a current in the 300A range

I understand but your simulation don't take this into account. Try to fit the coil with less density. The inductance is too high, my LCR multimeter says 297uH (5%)

Evgenij

Thu Mar 02 2006, 10:42PM

Registered Member #200 Joined: Sat Feb 18 2006, 01:49AM
Location: Pskov, Russia
Posts: 21

TheMerovingian wrote ...

I understand but your simulation don't take this into account. Try to fit the coil with less density. The inductance is too high, my LCR multimeter says 297uH (5%)

INPUT:
capacitance: 920uF
initial voltage : 300V
timestep: 100us
wire diameter (copper only): 0.8mm
double wire insulation thickness: 0.05mm
coil length: 30mm
coil internal diameter: 8mm
coil external diameter: 22mm
projectile diameter: 5.5mm
projectile length: 30mm
initial position: 3mm

OUTPUT:
Total resistance, Ohm: 0.95
Outline resistance, Ohm: 0.50 <-- I thinking this parameter doing low current
Coil resistance, Ohm 0.45
Turns of coil: 273.22
Wire length, m: 12.875
Initial coil inductance, uH: 342.19 <-- projectile in coil 3mm now
Projectileâ€™s mass, g: 5.559
Energy of caps, J: 41.4
Peak velocity, m/s: 14.559
Out velocity, m/s: 14.443
Kinetic energy, J: 0.580
Efficiency, %: 1.40
Peak force, N: 60,6 @ 700us
Peak current, A: 221,2 @ 500us

What approximate outline resistance you have?
I calculated as 0.35 Ohm SCR and solder and wire resistance + 0.15 Ohm capacitor's ESR = 0.5 Ohm

WaveRider

Fri Mar 03 2006, 10:15AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

BigShot reports an initial inductance of 304uH assuming 265 turns (only way to reduce winding density is by reducing the number of turns in the coil area). Multilayer coil inductance is indeed strongly dependent on the distribution of the windings!

I'll try to do a full motion simulation over the weekend.

Ciao!

Here's my simulation. I used the following parameters..

1. Capacitor Value (uF) 920.0
2. System Resistance (ohms) 0.0
3. Winding Conductivity (S/cm) 4.0e5
4. Quench Resistance (ohms) 1.0
5. Initial Capacitor Voltage (V) 300.0
6. Initial Coil Current (A) 0.0
7. Initial Armature Velocity (m/s) 0.0
8. Initial Armature Position (cm) 0.3
9. Initial Time Step Size (msec) 0.000025
10. Print out every ? times steps 1
11. Newton Method Tolerance 5.0e-3
12. Output Data File MERO2
13. Z-direction plot points 150
14. R-direction plot points 100
15. Number of contours in plot 15
16. FEM interpolation order 2
17. Exterior boundary type PEC
18. Armature triangle area factor 0.001
19. Sheath triangle area factor 0.09
20. Coil region triangle area factor 0.005
21. Air region triangle area factor 0.09
22. Switching position (for HB, D&Q) 3.0
1. Winding Length (cm) 3.1
2. Winding Thickness (cm) 0.7
3. Armature center hole radius (cm) 0.05
4. Sheath thickness (cm) 1.0
5. End Cap Thickness (cm) 1.0
6. Air Gap (cm) 0.125
7. Coil-sheath Air Gap (cm) 1.0
8. mu_i for Sheath 1.0
9. mu_i for Armature 5000.0
10. B_sat for Sheath (T) 0.5
11. B_sat for Armature (T) 2.0
12. Sheath conductivity (S/cm) 0.0
13. Armature Conductivity (S/cm) 4.0e4
14. Coil Wire Diameter (mm) 0.92
15. Armature Radius (cm) 0.275
16. Armature Length (cm) 3.0
17. Armature Point Length 1.0
18. Armature mass (g) 5.6

I fudged the coil wire diameter and coil length a tiny bit to get the required number of turns. I also made the armature conductive (although I ran a non-conductive case, and the difference was minimal).

The peak current is in line with what Mero has reported from his experiments (around 300A.. the plot shows about 320A peak current). The force is in the ballpark of Evgenij's results. I compute the max. force to be 77N (he computed 60.6...expected since his computed current is lower.) Final velocity is computed to be 15.6m/s...a little bit high, but I have probably underestimated your firing circuit resistance... With a bit more resistance in the firing circuit, it should give a pretty good answer...

Plot of current, force and armature speed.

Animation of the projectile motion and field lines.

[Edit: Fixed double post and oversized image. Remember 400 pixels is the maximum.]

first previous 2 3 4 5 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob