Ground proximity sensor

Thread Starter

Janis59

Joined Aug 21, 2017
1,537
Look for idea how to detect the falling object proximity to Earth before landing. The problem is speed, when for getting appropriate accuracy of required 2 meters plus minus 5 cm , at the 360-720 km/h corresponds to the 100-200 m/s thus 5 cm longs 0.5 ms to 0.25 ms. Thus, seems acoustic sensors are ultimate too slow, capacitative and inductive - too far field, infrared..... probably, microwave.... probably, however both are radiating strong fields by own and that is not good for the task where all spectra emissions ought be masked. What may be the simplest foolproof (and cheap) circuit for such task? Thought about steel ball in the thread, but experiments shown the wind is making false trigger.
 

Ya’akov

Joined Jan 27, 2019
6,856
In the spirit of brainstorming…

There is a kind of “tactical” (really more like tacticool) antenna that is essentially two tape measure type pieces of steel with the concave faces together, then covered in shrink tubing. It makes a rigid antenna when unfolded.

Maybe you could fold something similar in ~.5m lengths, then let it deploy before landing. The mounting on the object would be designed to let the open sensor slide up as it contacts the ground. I think it could be rigid enough to deal with the wind, perhaps.

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It’s too bad you can’t use radar because a 10.525GHz or a 24GHz cheap and cheerful sensor with IF output would be ideal—though it would need some CPU horsepower to deal with the signal.
 

Ya’akov

Joined Jan 27, 2019
6,856
One more idea, your ball on a string, but, an arrowhead shaped weight connected at three or four points instead of just hanging by one.

A central line could be used for the sensing. If you get a baseline on the up and down deviation of the weight as it falls, maybe you could distinguish actual contact by looking for more excursion that the drag produces.

I know it’s not as simple but anticipating problems with this idea, maybe the stays holding the weight could have properly calibrated spring loaded spools so they are always in tension, and the sensor line could use its tensioner to do the sensing with a rotary encoder.

OR, maybe the stays are sufficient and using the tensioner motion via rotary encoders could help filter false positives.
 

Thread Starter

Janis59

Joined Aug 21, 2017
1,537
In the spirit of brainstorming…

It’s too bad you can’t use radar because a 10.525GHz or a 24GHz cheap and cheerful sensor with IF output would be ideal—though it would need some CPU horsepower to deal with the signal.
Yepp, just russians probably are radiosounding the own playground and a "gift delivery service" may fail then. Research show that gift delivery at 2 m heigth is most effective to cancel their malplaying and unexpectedness is crucial to get the best satisfaction with the gift delivery.

By the way, about horsepowers - Polish and Chineese are soldering "Czujnik Mikrofalowy" (https://allegro.pl/listing?string=czujnik mikrofalowy&strategy=NO_FALLBACK), rather cheap and exists versions of 12V, it works on IC HCSENS0040 and then processor is simple "Arduino compatible" for 0.99 USD per piece. But it "luminates" too much in context of application.
 
Last edited:

MrSalts

Joined Apr 2, 2020
2,617
Add a 2m-long firing pin to the tip of the rocket.
Although, I'm not sure devices of war is an appropriate topic for a forum.
 
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