Sensing the impact of a projectile

I was speaking with a friend of mine who is a police officer. The topic arose of a need for a moving target on their practice range. I thought it would be a neat idea to mount a pop up target on a RC controlled mobile base. It would be best if we could detect the impact of a projectile on the target surface and in response, drop the target. The target surface would need to be disposable/replaceable and the electronics should not be destroyed when detecting the impact. How might one accomplish such a thing? Clearly, the mobile base would need to be armored against unintentional bullet strikes as well.

One way would be for the target to mechanically 'collapse' when it is hit (fold back, pop-down, whatever). This movement could then be picked up by a microswitch which would initiate the 'reset' of the target through whatever logic is required.

Piezo sensor on base of target to detect impact?

Piezo sensor on base of target to detect impact?

That's what I'd do.

I would recommend first deciding on the intended usage of the target and its basic functionality. Is it going to be a suspended target? Is it going to be a target attached to a track (to allow for constant path)? What firearms do they want to use with it? 5.56 rifles, tactical long guns (.308), handguns only? How big is the target they want to shoot at? man size silhouettes, 8 inch?
a man size silhouette mounted to be 6 foot tall that falls back can put some leverage on your movable holding device.
If using a switch where the target is going to fall backward, you target is going to have to have enough energy applied to it by the bullet passing through to overcome the force being used to hold it upright while the platform it is attached to is moving.
Basically, your target is going to have to be propped up so while moving it doesn't fall, but when hit it does. The cart will have to have enough weight to it that the target falling away from the shooter doesn't overbalance it and ideally be able to be reset remotely without having to walk down range.
A sensor to detect a bullet strike would also have to not give a false positive from the normal movement of the device.

Interesting idea.

The problem here is an issue of false positives. It would be a torso sized target attached to a mobile base. The issue gets more complex in that the base should be remotely controllable... Allowing for realistic engagement scenarios (a fleeing suspect, a dodging suspect, etc...) This means that not only do we have to detect the impact of the projectile on the target, but also billboard the target to the firing-line; always presenting the striking surface to the shooter. I was hoping to divide and conquer. Handle the detection first then the billboarding issue second.

I have setup a piezo element on a static target with the hopes that I can fire a few rounds through it and graph what is returned from it with an arduino... however weather and work have been conspiring against me. When it's nice enough to go shoot, I have to work and when I don't have to work, it's been hideous out.

So As I've been mulling this issue over in my head, I thought of something... ballistic chronographs (such as this one). These devices detect the passage of a projectile between two sensors and thus cab calculate the projectile's velocity. Perhaps a similar sensor could detect the passage of the projectile into the face of the target... So now to figure out how those gizmos work...

I have made a target sensor using the innards of a piezo speaker as sensor. Basically the "classical knock sensor".

It works perfectly well, and setting the treshold eliminates false positives.

I have however only tested it with a blowgun and a BB-gun (the firing range is closed for the winter).

There is an interesting document here:å

The military targets I have used, have been made either from an aluminum plate a couple of mm thick, or from polyethylene, 4-5mm thick.
The impact on the target from a high speed projectile is quite violent, and the target mechanisms and sensors are pretty overengineered. They have to be, they really take a good beating!
Targets were from "SAAB training systems".
The old version used a compressed air bottle and pneumatics, the new versions use electric motors to raise and lower the target.

The sensors on the older targets were micro switches with a weighted contact arm inside. Vibration would move the switch, and inertia would make the weight break the circuit.

Somewhere I have a couple of broken switches, if I can find them, I'll post a picture.

My main worry is to limit the signal going to the arduino.
With the microswitch it is easy: look for at break in the circuit.
But with the piezo, I'm afraid that I'll fry the pin with the generated voltage.

My main worry is to limit the signal going to the arduino.
With the microswitch it is easy: look for at break in the circuit.
But with the piezo, I'm afraid that I'll fry the pin with the generated voltage.


Pure gold!