Tuesday, November 23, 2010

Firing results and problems with noise

First: Firing results.

I've got sensors for the device now and thus can test speed again. I was firing from just one magnet at 400V. The capacitor stores 1,800uF so the device was carrying 0.5*0.0018*400^2 = 144J.

Slug weightVelocityEnergyEfficiency
4.8 g25.7 m/s1.59 J1.1 %
8.4 g22.5 m/s2.13 J1.5 %
11.6 g18.0 m/s1.88 J1.3 %

If all the gates worked at the same efficiency as the 8.4g slug (which they won't) the device will contain 28J of energy and reach 82 m/s. By comparison a 0.22 fired from a rifle will have between 100 and 300J of energy and will generally be doing more than 300 m/s. This slug will probably have better penetration, however, given that it'll be a pointed chunk of hard steel rather than a soft and dull lead slug.

In other news, getting the second gate working was a bit of a challenge. The charger is giving me a bit of trouble in that is makes so much electromagnetic noise that it creates jitters in the optical sensor of the second gate. I've tried adding a low pass filter but for some reason it's actually causing the optical sensor to just read low. Instead, I'm simply making the charge switch also force the sensor into the non-firing position. I've not yet completed this work but I'll have that soon.

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