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Velosats
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Please be positive and constructive with your questions and comments.

Velosats

by animefruit on Tue Feb 25, 2020 1:14 pm

This is Neal Cole.I am currently trying to find a sensor that can read the pressure of nerf bullets hits.I am currently using a velosat from Adafruit but the readings are wacky.Is there some way I can use this velosat without the readings being wacky?Or if not, is there some other pressure sensor that would be able to read nerf bullet hits?

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Re: Velosats

by adafruit_support_bill on Tue Feb 25, 2020 1:51 pm

I don't know of any film-type sensors that will give you a precision reading. You will probably have better luck using an accelerometer. Based on the mass of your target and your projectile, you should be able to calculate the impact force from the acceleration.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 7:51 am

This is Neal.Can I still get a big area it will sense with a accelerometer?I am thinking about an 8 by 8 inch’s in size.

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Re: Velosats

by adafruit_support_bill on Sat Feb 29, 2020 8:49 am

Yes, it can sense over a large area. But you will need to put some thought into the design of your target

If you have a target suspended (e.g by strings) so that it can move when hit, the force of the impact will cause the target to accelerate. If the mass of the target is 100 times the mass of the projectile, the acceleration of the target will be 1/100 of the deceleration of the projectile. Since force is equal to mass times acceleration, you can calculate the force of the impact.

The problem is that an off-center hit will cause the target to twist, so one side will accelerate faster than the other. In that case, a center mounted accelerometer will not record the true full force of impact.

You could handle that by putting an accelerometer on each corner and taking the average of the 4. One benefit of that is that you could also calculate the point of impact based on the differences in acceleration between the 4 sensors. The down-side of that approach is that there are 4 times as many sensors to read and it might be tricky to do it fast enough to catch the moment of peak impact for all of them.

Another way to deal with off-center hits is to mount your target in a way that allows it to move back when hit, but keeps it from twisting. Something like suspending it from a long swing arm could work.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 9:11 am

This is Neal.I am sort of doing using this as a device to put on people.I don’t want it to be reading high values when people move.Will it read that when they move.And if so,how can I solve that problem?

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Re: Velosats

by adafruit_support_bill on Sat Feb 29, 2020 9:43 am

The accelerometers will detect motion as people move around. But it will be typically be pretty low-level compared with a projectile impact. You should be able to filter that out i software.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 9:47 am

Ok.I guess I will get some accelerometers and try them out.Thankyou.If I have any more questions,I will ask.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 10:05 am

This is Neal.So do I still need to make these accelerometers suspended by strings if it is going to be on people?

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Re: Velosats

by adafruit_support_bill on Sat Feb 29, 2020 10:15 am

To sense over a large area, the target would need to be fairly rigid. Something like a body-armor plate should work. You would not need to suspend it, but you probably want a bit of soft padding behind it so that it will compress when hit.

That makes the force calculation more complex. But I suspect you are more interested in relative impact force than in absolute values.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 11:45 am

This is Neal.Ok.If I have any more questions I will ask you.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 12:00 pm

This is Neal.So I am using this to mostly sense nerf bullets.So would an armor plate be not good for that matter?

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Re: Velosats

by adafruit_support_bill on Sat Feb 29, 2020 12:12 pm

It does not need to be heavy. Just stiff enough that the whole plate will move if it gets hit anywhere. The accelerometer is measuring acceleration. If the it doesn't move, it won't register a hit.

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Re: Velosats

by animefruit on Sat Feb 29, 2020 12:28 pm

This is Neal.Is there any accelerometers that you would recommend for my project?

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Re: Velosats

by adafruit_support_bill on Sat Feb 29, 2020 1:02 pm

The LIS3DH would be a good choice. It has selectable sensitivity between +/- 2G and +/- 16G. So you can adjust it for best results.
https://www.adafruit.com/product/2809

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Re: Velosats

by animefruit on Sat Feb 29, 2020 1:16 pm

This is Neal.Ok I will try that.I will let you know when I have any questions.

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Please be positive and constructive with your questions and comments.