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I'm using a HC-SR04 sensor to detect obstacles. What are the pitfalls with an ultrasonic sensor?

Here are a couple I've found during my testing:

  • The signal can bounce off of one wall to another and then get picked up, distorting latency
  • Absorbent materials sometimes don't bounce the signal back
  • Check the datasheet for supported range (min/max)
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  • $\begingroup$ Welcome to Robotics Jacksonkr, but I'm afraid that Unbounded Design Questions are off-topic because there are many ways to solve any given design problem, so questions that ask for a list of approaches or a subjective recommendation on a method (for how to build something, how to accomplish something, what something is capable of, etc.) are off-topic. $\endgroup$
    – Chuck
    Jul 7 '16 at 17:27
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    $\begingroup$ That said, I think this might be a candidate for a conversion to a wiki. I'll see if it's possible and will report back when I get more information. $\endgroup$
    – Chuck
    Jul 7 '16 at 17:29
  • $\begingroup$ @Chuck I rephrased it to make it more of an objective answer. If it would do better as a wiki I'm happy to do whatever I need to in order for that to happen. $\endgroup$
    – Jacksonkr
    Jul 7 '16 at 23:24
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    $\begingroup$ Hi Jacksonkr. As you know by now we prefer practical, answerable questions based on actual problems that you face, so I think two questions of the form "How can I deal with the signal bouncing off of one wall to another and then getting picked up, distorting latency" and "How can I deal with absorbent materials sometimes not bouncing signals back" would be better. As you find more pitfalls, ask about those as separate questions too. The problem with list questions like this is that there can be no definitive answer. $\endgroup$
    – Mark Booth ♦
    Jul 8 '16 at 10:36
  • $\begingroup$ Incidentally, Community Wiki is not a way to make a list question acceptable. It was an early solution to a problem which no longer exists (because anyone can suggest edits) so it has very limited application these days. $\endgroup$
    – Mark Booth ♦
    Jul 8 '16 at 10:44
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From my experience, don't use them for obstacle detection on high speed robots. Your'e just as good as without using them.

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    $\begingroup$ Bats are pretty high-speed and use ultrasound just fine for obstacle detection and avoidance. It may be that your experience with ultrasonic sensors is negative due to poor system design or integration rather than a limitation of the technology itself. $\endgroup$
    – SteveO
    Jul 7 '16 at 16:35
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    $\begingroup$ @Jacksonkr I was tryin to use em with my autonomous car, about 7-8 m/s, HC-SR 04 failed horribly, and I broke a few parts in the collisions $\endgroup$
    – YaddyVirus
    Jul 7 '16 at 16:47
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    $\begingroup$ @SteveO The Doppler's effect in this case renders my sensors useless. These sensors aren't bats, and hence, cannot detect changes in frequency that occur in my case, hence useless. OR if they aren't, I'd love to know a way they work $\endgroup$
    – YaddyVirus
    Jul 7 '16 at 16:48
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    $\begingroup$ Interesting @YaddyVirus. Sounds like you needed a wide-bandwidth ultrasonic receiver. If your robot was moving toward a stationary object at 100 mph, a 40kHz ultrasonic signal would appear to be about 34kHz - still in the ultrasonic range. There are receivers that cover wide bandwidths but I don't know how cost-effective they are. $\endgroup$
    – SteveO
    Jul 7 '16 at 17:02
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    $\begingroup$ Oops! You're right @Chuck. $\endgroup$
    – SteveO
    Jul 7 '16 at 17:45
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It'll involve a bit of reading, but Johann Borenstein's papers include several 1980s-90s publications about ultrasonics (plus loads of other interesting stuff). Some pure ultrasonic systems, some mixed with other navigation techniques.

One interesting effect I read about was reflections. If the "beam" hits a wall at an oblique angle, then instead of reflecting back to the sensor it bounces on back into the room, hits something then bounces right back. The result is detecting things that appear to be "beyond" the wall, but really they're objects in the room but a longer path length is being measured.

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