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I needed to figure out exactly how much power the airsoft guns actually use. Voltage is pretty straightforward: the battery's nominal voltage is 11,1V so under load it will probably be a bit below that.

Current, however, is rather more difficult to measure. My multimeter is only good up to 10A and I expect higher current than that.

Luckily, I have data loggers on two of my remote controlled helicopters which are also electrically powered and run on 37V batteries up to 80A (yes, that is a lot) so they should be perfect.

So I went and connected the guns to one side of the data logger and the battery to the other, plugged in the USB lead, started the application and set it to live recording. Here are the results.

First the M110 gun:

Current and voltage: M110 (click for large version)

And here the M130 gun:

Current and voltage: M130 (click for large version)

The first shot draws significantly more current than the rest. This is seen clearly both when firing on semi-auto and on full-auto.

The M130 gun draws more current but not a lot more.

Based on these measurements I settled on a maximum current of 60A and a continous current of 20A.

This is the kind of data logger I use: Eagle Tree eLogger

What's the point of making robots if you can't mount lasers to them?

I am not making robots and I don't have any deadly lasers lying around. I do however play airsoft and I thought it would be neat to have a remote triggered, automatically firing gun which could be set up and left waiting for unsuspecting bad guys to wander into its line of fire.

Somehow, I settled on the following basic setup:

Two units: a sensor/transmitter and a receiver/trigger. The sensor would be placed where it can detect people that should be fired upon and the trigger unit will be connected to the gun.
Communication will be wireless using nRF24L01+ units, the sensor will be a passive infrared motion  sensor (like the ones turning on the lights in the garage), gun will be triggered by a power MOSFET and both the sensor unit and trigger unit will be controlled by an ATmega168.

An Arduino will be used in the prototyping phase for testing the various components but the I will probably move over til plain C (avr-lib) at some point. Read the entire post »