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Mars helicopter employs advanced control techniques to survive in-flight anomaly

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Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#91

Post by caconym_ »

stevenhuang wrote: post #86
caconym_ wrote: post #84

Earlier quoted context omitted.

> While I understand you're trying to point out hubris, you're swaying the other way and appealing to authority. I'm appealing to the fact that they sent the thing to Mars and flew it. If you think "any hobbyist" could have trivially done a better job, which seems to be essentially what you're saying, there isn't much for me to say to you other than that I strongly disagree. And if I'm supposed to be the one who's ap…

They expected the camera not to drop frames. Their optical flow system tracked time independent of actual frame time. Anyone who've done optical flow or even anything with video recording on embedded devices knows these are known failure modes, and should be handled properly. That is what's being discussed here, this is the failure mode in question. So yes, those experienced in optical flow and embedded control syste…

> They expected the camera not to drop frames [...] That is what's being discussed here

It isn't, actually. The comment I responded to, and the one it linked to, are broadly criticizing the sensor fusion/control loop implementation--the thing that saved Ingenuity after the optical flow subsystem started returning bad data. That's what's being discussed here, in the context of this subthread where I entered it.

The dropped frame thing is much more cut and dried, and it's obviously a bonehead mistake. It's also the kind of thing that's always going to happen, as you say. Many of the commenters here seem to be generally at odds with that reality--I don't believe the state of the art in software development has yet achieved guaranteed bug-free implementation of diverse real world applications, but you wouldn't think that from reading some of these comments (e.g. the one you linked above).

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#92

Post by jamiedamien »

heisenbit wrote: post #90

> the inertial measurement unit (IMU) and the navigational camera. The IMU measures acceleration in three dimensions, using data from several sensors to estimate altitude, velocity, and position. Even though this system samples at 500 Hz, the error would accumulate over time, causing the helicopter to become lost quickly. I understand the IMU is not an ideal input and integration over time leads to positional errors.…

I suspect what happened is that the position and velocity estimates from the VIO system (cameras) were wrong (and perhaps wildly jumping) and since position and velocity errors are inputs to the attitude controller, the tilt oscillated as well. It's not that the IMU did a poor job estimating attitude (tilt), but rather that the attitude controller was asked to tilt in erratic directions to compensate for the erratic and incorrect position and velocity readings.

It's quite hard to detect when position and velocities are "obviously incorrect", especially when they come from VIO, where the optimization result can jump around in non ideal conditions, so I'm not surprised there was not a more graceful anomaly detection.

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#93

Post by 4gotunameagain »

ncmncm wrote: post #55
rsp1984 wrote: post #52

Fusing video with IMU for navigation is called VIN (visual-inertial navigation) or VIO (visual-inertial odometry) and the field has made enormous progress over the last 10-15 years. It's the same technology that the iPhone uses for all its AR features. Dropped frames are one of the easiest things to handle. Yes, the visual feature tracking depends on frames of video but even cheap phone IMUs these days are good enoug…

It means that the people who know most about closed-loop vehicle control were not involved in the design of the copter. Such fragility is a really elementary design mistake any experienced engineer would not make. Certainly the vehicle that delivered the lander would not suffer from the same mistake. My interpretion is that the copter, as an inessential system component, was seen as an opportunity for junior people t…

A quick search would have you know that the lead of the navigation for the copter is David S. Bayard, an awarded scientist in the control field in NASA.

So maybe the issue is not as simple as a news article portrays it

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#94

Post by techrat »

app4soft wrote: post #77
rsp1984 wrote: post #52

Fusing video with IMU for navigation is called VIN (visual-inertial navigation) or VIO (visual-inertial odometry) and the field has made enormous progress over the last 10-15 years. It's the same technology that the iPhone uses for all its AR features. Dropped frames are one of the easiest things to handle. Yes, the visual feature tracking depends on frames of video but even cheap phone IMUs these days are good enoug…

> It's the same technology that the iPhone uses for all its AR features iPhone was not a first. "Agent V" (2006) — a mobile AR game preinstalled on Nokia 3230 already has such technology.[0] [0] https://news.ycombinator.com/item?id=20957157

1) He didn't say iPhone was first.

2) Was this something you even really needed to "Well, ackshully..." anyway?

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#95

Post by xtiansimon »

idiotsecant wrote: post #8
njoubert wrote: post #5

I see no mention of "advanced control techniques"? Sounds like there is just a limit on roll/pitch angles and a limit on distance applied. Saying "advanced control techniques [for multirotors]" sets an expectation for something along the lines of Tedrake's Underactuated Control approaches: http://underactuated.mit.edu/

Sensor fusion is part of the control system. Sensor fusion that incorporates visual information is outside of the typical classical controls sphere and is likely considered part of an advanced controls segment of the devices firmware as opposed to the bog standard deterministic controls algorithm. You need not gatekeep here, this is a real term.

> “You need not gatekeep here, this is a real term.”

Not my monkey; not my circus. But… is critique of terms “gatekeeping”? I understand this term in the context of ownership (ie. gatekeepers for books are publishers/printers who own the means of production.)

I greatly appreciate some level of debate of terms here on HN.

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#96

Post by ncmncm »

4gotunameagain wrote: post #93
ncmncm wrote: post #55

Earlier quoted context omitted.

It means that the people who know most about closed-loop vehicle control were not involved in the design of the copter. Such fragility is a really elementary design mistake any experienced engineer would not make. Certainly the vehicle that delivered the lander would not suffer from the same mistake. My interpretion is that the copter, as an inessential system component, was seen as an opportunity for junior people t…

A quick search would have you know that the lead of the navigation for the copter is David S. Bayard, an awarded scientist in the control field in NASA. So maybe the issue is not as simple as a news article portrays it

Then, apparently the real-time attitude-control feedback loop was delegated to somebody else less experienced. Navigation is a wholly different responsibility that may happen to rely on input from some of the same hardware.

On the other hand, scientists are often not as good at design as engineers. They are not routinely trained in it, and are expected to deduce it from first principles. (If you have seen code written by scientists, you will know what I mean.) When they err, it is typically by assuming that theory and practice are the same.

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#97

Post by ncmncm »

ehsankia wrote: post #56
ncmncm wrote: post #55

Earlier quoted context omitted.

It means that the people who know most about closed-loop vehicle control were not involved in the design of the copter. Such fragility is a really elementary design mistake any experienced engineer would not make. Certainly the vehicle that delivered the lander would not suffer from the same mistake. My interpretion is that the copter, as an inessential system component, was seen as an opportunity for junior people t…

The article makes it sound like after the missed frame, every subsequent frame had the wrong timestamp and was processed wrong, so it sounds like more of a bug. If the subsequent timestamps had the right timestamps, and the calculation was based on delta timestamps, then it would basically basically interpolate over the missing frame and then recover. The fact that every subsequent frame was assumed to be 33ms in the…

For a real-time attitude-control feedback loop to have been subject to upset by such a bug is, exactly, the design flaw.

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#98

Post by idiotsecant »

krisoft wrote: post #26
jessriedel wrote: post #18

Earlier quoted context omitted.

I don't think this is gate keeping. Regardless of the terminology used within the field, the intended audience of this pop article will interpret "advanced" to mean actually unusual or at the cutting edge. Relying on the public's misinterpretation of jargon ought to be criticized.

> ... intended audience of this pop article ... Are we reading the same page? I see datasheets linked in the navbar, an article about an EtherCan box, and white papers about encoders. If any site is then certainly this one has a very specialist audience in mind. Besides i believe what constitutes "advanced" gets wider rather than narrower when you move towards a less specialised audience. To the generic population ev…

In the motion control and process control industries deterministic systems or SISO systems like PID are typically considered in what someone would just call 'controls'. Advanced process control is an actual industry three-letter acronym term relating to 'meta-controls' where the controller is itself controlled by an outside system like the supply chain or a plant tuning system, etc. This is the point I was trying to make - i'm not making a judgement call on what is or is not sufficiently 'advanced' only pointing out that this term has a meaning that the parent post I was replying to might not have understood.

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#99

Post by renewiltord »

stevenhuang wrote: post #87
renewiltord wrote: post #71

NASA systems appear to have the property that they are both perfectly designed when HN commenters do not understand the code and amateurishly designed when they have errors. This bathtub style curve for perception of NASA design by HN commenters makes me question if the perception correlates with reality.

Perfectly designed when it's right and badly designed when it's wrong, you mean? Strange way to state a tautology to make yet another boring statement on ye olde HN commenter.

No, actually, I do not mean that. I mean exactly what I said.

Re: Mars helicopter employs advanced control techniques to survive in-flight anomaly

#100

Post by app4soft »

techrat wrote: post #94
app4soft wrote: post #77

Earlier quoted context omitted.

> It's the same technology that the iPhone uses for all its AR features iPhone was not a first. "Agent V" (2006) — a mobile AR game preinstalled on Nokia 3230 already has such technology.[0] [0] https://news.ycombinator.com/item?id=20957157

1) He didn't say iPhone was first. 2) Was this something you even really needed to "Well, ackshully..." anyway?

> 1) He didn't say iPhone was first.

I'm not argue. I'm just saying.

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