Thread: DIY Steel Plate Impact Detection

Originally Posted by janleroux

For a month or two I have been tinkering with this steel plate impact detection idea for when you go practising target shooting on your own. I found it sometimes difficult to hear a hit (earplugs) and to see the hit (recoil or dare I admit it - old age). I got it working and today I took it to a dog-walk park with my son and tested it all the way to 350m.

Here is a video of it working in my workshop: https://youtu.be/7acWxYwWrTg

50m test: https://youtu.be/jYXJJbm0JaI

100m test: https://youtu.be/ID9QplH6RR8

200m test: https://youtu.be/JgVao70CrxY

350m test: https://youtu.be/f0KK7jSD3as

I tend to over-think/over-engineer things, so what sort of range would one need to make it work at to be really useful - will 2 km be enough?

Any all ideas and feedback appreciated.

Looking at it I have the same concerns as someone mentioned about pass through or damage from the plate being hit HARD. How much impact does the sensor need to have? Does it need to be attached to the back of the plate? Something to try would be to attach it to the back of the post. See if enough energy passes down the post to trigger it there,If so you could put a protector / deflector plate in front of the sensor so that a pass through or miss does not damage the sensor. And if it works there, would it work at the bottom of the post with protection in front of it?

Originally Posted by timattalon

Looking at it I have the same concerns as someone mentioned about pass through or damage from the plate being hit HARD. How much impact does the sensor need to have? Does it need to be attached to the back of the plate? Something to try would be to attach it to the back of the post. See if enough energy passes down the post to trigger it there,If so you could put a protector / deflector plate in front of the sensor so that a pass through or miss does not damage the sensor. And if it works there, would it work at the bottom of the post with protection in front of it?

If you have decent plate you won’t get a pass through.

Originally Posted by Shootm

If you have decent plate you won’t get a pass through.

Thats quite true, But there is also a hell of a jolt when bullets hit the plate and while in might react well to a hammer hitting it how will it last with the inertia of a bullet impact repeatedly? A 20 oz hammer doing 20ft per sec (light tap ) is 8ft/lb. I bullet impact will be a near instantaneous impact nearly 10 times giving it a decent swing with a sledge hammer (8lb sledge at 50fps is 49 ft/lb ) There is a lot of energy transferred. The reduction of impact as carried through the post may well see the gear last longer .....

I really like the idea and I am not trying to be critical. I am trying to see if you can do this isn a way so that you get a decent life out of it. It sounds very interesting.

There's also the thought that a sound detector/mike installed nearby to catch the ring of a struck plate might work.

It wouldn't have to be on the plate, just close enough to work well enough.

Originally Posted by Shootm

Bring it up to the Toby shoot
Just out of curiosity what sort of cost to put that together?

Will be more than happy to put a couple of units together for the Toby shoot. How many gongs will you have out on the range?

Cost - I have not done the calculation yet. But this is based on Arduino (cheap as chips), and components off AliExpress (like the enclosure, antenna, etc). The most expensive part is the radio chip ($15) and the 14500 Li-ion battery ($12) and the actual pcb ($15). My aim was to do this for less than $100 per unit, and at this stage I am sure that it is coming in way under that. I have also already built in a Solar Charging circuit, but I have not tested it yet - I do not think you want to run around replacing batteries all the time. Will keep you posted.

Originally Posted by timattalon

Looking at it I have the same concerns as someone mentioned about pass through or damage from the plate being hit HARD. How much impact does the sensor need to have? Does it need to be attached to the back of the plate? Something to try would be to attach it to the back of the post. See if enough energy passes down the post to trigger it there,If so you could put a protector / deflector plate in front of the sensor so that a pass through or miss does not damage the sensor. And if it works there, would it work at the bottom of the post with protection in front of it?

It is possible to play with the sensitivity of the sensor, but outside of the enclosure if you tap it with your finger it will be sufficient. Inside the enclosure a light pat with your hand on the box will trigger it. I have actually tested it on the post in the workshop, and it worked without an issue - I had to hit the plate a bit harder with the hammer (harder than what you see in the video clips). So if you mount the sensor box on the frame where the impact jolt will be transferred, it should be working fine. I see some more testing coming...

Originally Posted by timattalon

Thats quite true, But there is also a hell of a jolt when bullets hit the plate and while in might react well to a hammer hitting it how will it last with the inertia of a bullet impact repeatedly? A 20 oz hammer doing 20ft per sec (light tap ) is 8ft/lb. I bullet impact will be a near instantaneous impact nearly 10 times giving it a decent swing with a sledge hammer (8lb sledge at 50fps is 49 ft/lb ) There is a lot of energy transferred. The reduction of impact as carried through the post may well see the gear last longer .....

I really like the idea and I am not trying to be critical. I am trying to see if you can do this isn a way so that you get a decent life out of it. It sounds very interesting.

Very good feedback, good to hear the potential weaknesses to see how one can mitigate it. Potting up the electronics inside the enclosure is going to be important to get a decent life time out of it - you do not want components and solder joints to come lose. The challenge is going to be to have one unit that fit all applications - a 22LR as well as a large cal. Using something like this on short ranges for large cal (less than 350m) probably does not add much value, but it might be helpful for the 22's. But shooting at 800m+ on large cal's might be.

The best is going to be to get some of these units out in the field, and shoot at them until they break - and how they break.

Originally Posted by Max Headroom

There's also the thought that a sound detector/mike installed nearby to catch the ring of a struck plate might work.

It wouldn't have to be on the plate, just close enough to work well enough.

I tried microphones on my beehives some time ago, where I thought I could determine bee activity inside the hive, but the wind created havoc on my setup - so much so that I binned that idea. Here in Wellington I got such a range from no wind days, to typical Wellington days where the mic was complete useless because of wind noise. I am saying days, but some days we have all the seasons in one day. I suspect that having the gongs out on the hills will create similar challenges.

The interesting part with the mic could be to detect a miss - if the projectile is still supersonic when it passes, but did not hit the plate. Maybe something to experiment with for version 2.

So, just came back from doing some more testing after the morning service. VERY happy with the results.

Attachment 111604
1500m test: https://youtu.be/Phyx9ULvIBw

Attachment 111605
2000m test: https://youtu.be/Hc9wBhCbCp0

Originally Posted by janleroux

I tried microphones on my beehives some time ago, where I thought I could determine bee activity inside the hive, but the wind created havoc on my setup - so much so that I binned that idea. Here in Wellington I got such a range from no wind days, to typical Wellington days where the mic was complete useless because of wind noise. I am saying days, but some days we have all the seasons in one day. I suspect that having the gongs out on the hills will create similar challenges.

Yes, good point. I was assuming zero other noise, which in hindsight isn't practical.

Originally Posted by janleroux

So, just came back from doing some more testing after the morning service. VERY happy with the results.

Attachment 111604
1500m test: https://youtu.be/Phyx9ULvIBw

Attachment 111605
2000m test: https://youtu.be/Hc9wBhCbCp0

Clearly range isn't the weak link. 2km is ample.

Originally Posted by Max Headroom

Clearly range isn't the weak link. 2km is ample.

Yes, I am happy with the range. And to be honest I have not done any antenna matching or even tried to improve the radio coms. If I slow the radio down, then the range will automatically also increase.

I will put some time into moving the circuit over to a pcb, then we can get a couple of test units build.


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How about having the unit/enclosure hanging on a wide, or possibly 2, lightweight straps that hang it down the back of the plate, maybe even a magnet to keep it flush on the plate. Make the straps lightweight and easily replaceable if hit on the front of the plate, was thinking something like the strapping type material they use for strapping up bundles of posts, approx 1mm thick by about 30mm wide.

Originally Posted by Husky1600

How about having the unit/enclosure hanging on a wide, or possibly 2, lightweight straps that hang it down the back of the plate, maybe even a magnet to keep it flush on the plate. Make the straps lightweight and easily replaceable if hit on the front of the plate, was thinking something like the strapping type material they use for strapping up bundles of posts, approx 1mm thick by about 30mm wide.

Not 100% sure I understand your explanation about the straps. Are you thinking the straps should have some sort of a hook attached on one end that hooks onto the top of the plate, and then the other end is fixed to the enclosure? That together with the magnets then keeps everything in place?

This is an idea worth investigating a bit further. I’ve got a couple of Neodymium magnets that I took out of old hard drives and they are strong enough to even hold a large hammer. So you wont need much more to keep the enclosure stuck to the back of the plate. Will just have to figure out how the magnets attach to the enclosure - maybe epoxy?


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Surely an appropriate thickness and grade of Hardox would remove the possibility of pass-throughs. A thin quality double-sided tape such as 3M 5925 VHB should allow for sufficient acceleration transfer. I don't see SM components being troubled by the impacts, but batteries and their housing/contacts, and the antenna SMA maybe.
Just off the top of my head I would have thought that the RF side would be the most problematic in terms of intermittency, what with the TX radiating from behind the plate and without the option of maintaining line-of-sight between the antennas. Would you mind providing a link to the RX / TX pair you are currently using please so I can give it further thought ?