http://www.allaboutcircuits.com/technical-articles-preview/36582

Dear author and reviewers,

Here are the results of my technical review. One purpose of this review is to facilitate discussion and input from other AAC contributors. If the reviewer community decides that a particular issue does not require revision, all the better—leave it as is. Any issues that are deemed significant enough to require revision should be addressed before the article is published.

If I have botched or missed anything, please bring me in front of the class and apply the dunce cap. That’s how I learn.

Thanks to all for your time and expertise.

1. “helping them maintain station”

I did a Google search to try to figure out what “maintain station” means, and I found one result that says “maintain station is when the following boat or boats match the heading and speed of a lead boat while maintaining a specific position relative to it.” This doesn’t seem too applicable to “space hardware” or even to spacecraft because (as far as I know) we don’t have multiple spacecraft flying in formation. Is there any way to clarify this, or I am simply embarrassing myself with my ignorance of aerospace terminology?

2. “and the deviation will drift with the satellites.”

This seems a little unclear. Are you referring to the motion of the individual satellites or the effects of acquiring new satellites?

3. “and some damn good topological maps”

I think this should be “topographical maps” (actually, “topographic” is the more standard spelling in American English, but both are acceptable).

4. “Less obvious is what happens when you put multiple tranceducers”

I assume that should be “transducers.” However, I think you should stay with “sensors” because that is the terminology you use in the surrounding text, and using a different word might make readers think that you are talking about something different.

5. “Even single sensors must cope with cross-talk from themselves”

This is more for my edification, but is LIDAR susceptible to self-crosstalk? I would think that the focused nature of the laser would essentially eliminate that problem.

6. “it’s picking up gravity, linear acceleration, centrifugal forces from rotation, vibration”

This is more for the sake of discussion. Is it correct to use “centrifugal” here instead of “centripetal”? I can’t get past the fact that the centrifugal force is “fictitious”; it’s a word we use to describe the way we experience the real force, i.e., the centripetal force. But an accelerometer doesn’t “experience” things the way humans do, so it seems like the force that it is reacting to is the centripetal force.

7. “If you’re confined to the ground (instead of flying around like a fool), that's really all you need.”

Why would a quadcopter be confined to the ground?

8. “then some accelerometer upwards gets into the sideways when it shouldn't”

I’m not sure what you mean by “gets into the sideways.”

 

Hope I'm using this right. I'll go down the list...

1. Yup, "Maintaining station" is absolutely a boating "mooring" term, merely applied to satellites, which have all the same issues but in space. (I suppose earth is the lead boat in the analogy.. I didn't know that part of it.) You're right it's not usually applied to spacecraft - even the shuttle tends to move around in orbit. But satellites have to sit in a predefined position for ages and keep their "heading" relative to star markers, gyros, and ground telemetry. I believe I got the term from listening to space engineers give talks, though I couldn't give you a reference. They loooove the Kalman filter.

2. Both, usually. Sorry about the vagueness, but "what affects GPS signals" is a whole Pandora's box. Polarization angles off nearby buildings, atmospheric phase shifts, even General Relativity is involved. I tried to indicate "it's complicated" without getting into it too much. Gaining and losing new locks as sats go over the horizon creates the most obvious 'discontinuities' in position, but hourly drift and Selective Availability are always there too. In some ways they're worse, because they _look_ consistent over small timescales, but they're not.

3. Good catch, this is a tricky terminology one and yes, probably depends by country and even profession. My interpretation is maps are "topographical" - literally drawings of shape. But a 3D model of the landscape is "topological", literally a measurement of shape. At parks and wildlife we'd work with high-res "digital topology" ("digital elevation maps") for planning things like water drainage where we didn't care what colour the ground was. Hiking maps are a combo of "graphical" and "topology" thus "topographical" is right for them.

4. Bad spelling, no problems. Surprised my checker didn't spot it. I could make a distinction between "sensor" as a package and "transducer" and the physical sensing element because some packages have multiple, but that's the digression I was trying to avoid. I'll change it to sensor.

5. Yup, even Lidar, although "long lasting echoes" are a vastly smaller problem with light, unless mirrors or optical resonators somehow get involved. If you're laser-ranging the moon you can't exceed 1Hz. Most system are much shorter range though, so electronics become the limiting issue. Assuming you mean pulse-lidar, (that works off timing and high-speed photodiodes) and not the "cheap" version which just shines flat light and looks for the reflections.

6. I wondered about that myself. I think the issue will persist as long as chem labs call them "centrifuges" rather than "centripedes", and I think an academic would need to settle the argument about whether the sensor feels the pure centripetal force, or measures the "centrifugal reaction" via the acceleration-sensing element. I honesty don't know.

7. Not if it's working properly but most other robots and sensor package systems do, and I like to be inclusive. Did you know that NASCAR uses full Kalman filters in their live-car-tracking "GPS" systems? The cars move so fast, so they have to run a full sensor-fusion plus driver inputs (steering wheel and pedals) system to get sub-meter accuracy. Cars and space satellites is where a lot of the practice was refined. (And WiMotes)

8. Yeah, explaining that takes another two paragraphs that probably makes it worse, but I'll try. We know the sensor is moving flat along the table at all time, but it's also rotating, so we're depending on the system knowing the rotation state at any moment to transform the sensor's accelerometer vectors properly back into the flat plane. The accelerometer and gyro reading can be perfectly accurate on their own, but if we allow the timing to drift and we 'mismatch' the fusion between the sensors, (ie: we use an earlier gyro reading for a different angle) there will be a 'leak' into the perpendicular axis that we know _wasn't_ the direction of travel. Some sideways will get into the upwards.

For something like a rolling ball (sphero) this is always happening, but I though the "flip halfway" example would create an obvious point in time that, if you move or delay, would screw up the interpretation.

 

In regards to item 1: stationkeeping is a nautical term I'm familiar with and orbital station-keeping is another. Whether you use one of these or the terminology you currently have, defining the term in it's first use would be helpful to most readers.

 

In regards to item 1: stationkeeping is a nautical term I'm familiar with and orbital station-keeping is another.

I do like "orbital station-keeping", which Is the other term I've heard for it. I'll change it to that, hopefully it's explicit enough not to need defining inline. (Already way over the WC, and I digress too much as it is)

 

The article is generally hard to follow, with awkward phrasing, fragmentary structure and downright weird use of quotes and colloquiallisms. The two included photographs add nothing but splashes of color.

 

Hi Jeremy,

Thanks for the extensive feedback, I appreciate it.

1. Revise as you see fit (thanks for the input, KJ6EAD). It probably makes sense to avoid a definition if possible because the article is rather long. However, a brief definition/explanation might be helpful for readers.

2. I think we can leave this as is, unless you can think of a quick and easy way to make the statement somewhat less vague.

6. I don't know either. Unless we get some input from a physicist, we'll leave it as is.

8. Don't overburden yourself. We don't need a full explanation, and it's fine if the reader doesn't have the whole story. What we want to avoid is a sentence that leaves the reader feeling bewildered.

Just let me know when you're finished with the revisions.

 

1. Revise as you see fit (thanks for the input, KJ6EAD). It probably makes sense to avoid a definition if possible because the article is rather long. However, a brief definition/explanation might be helpful for readers.

I changed it to "orbital station-keeping", since I think those words are mostly self-explaining, and changed "spacecraft" to "satellite" so it would be clear which spacecraft I meant. I hope that's enough, we could link to a definition but google exists. It was really just supposed to be a background reference indicating where Kalman has seen real use and why people should trust it - if it's getting in the way, we should cut it.

2. I think we can leave this as is, unless you can think of a quick and easy way to make the statement somewhat less vague.
I could cut it entirely, but I was trying to indicate "here be dragons" (the vaugeness dragon, I suppose) because otherwise people might go trusting GPS systems when they really shouldn't. (and you get that famous Wedding Groom getting beaned by a quadcopter video) If I at least introduce the idea, they can follow it up themselves. But I can barely think how I'd sum it all up in an article, let alone a paragraph, sorry. I'll leave as-is unless you want it gone.

6. I don't know either. Unless we get some input from a physicist, we'll leave it as is.
Agreed. Either way I'm gonna get yelled at, but everyone at least knows what "centrifugal force" means.

8. Don't overburden yourself. We don't need a full explanation, and it's fine if the reader doesn't have the whole story. What we want to avoid is a sentence that leaves the reader feeling bewildered.
Similar to 2, I don't want to leave people with a false sense of knowing, without pointing out a few lurking dragons that they'll have to deal with if they get into this stuff. Temporal fusion issues end up being the biggest and hardest to track down, exactly because it's such a subtle concept. Noobs looks at the spec sheet and check the sensitivity rating, pros check the timing guarantees because they know that affects the outcome more than pure resolution. If I don't raise that somehow, they're going to find out later the hard way. But if I've gone as far as bewilderment, then I should fix that.

I'll have another look at the phrasing, but I've gone over it so many times now I'm loosing my objectivity. Is it the concept, or the way I've put it? I could come up with another example. Maybe a diagram would help?

Just let me know when you're finished with the revisions.
Going through it now, made the easy ones, working on that last section again. By the time you read this, I'll be done. ("finished", or "abandoned"?)

Oh, and I added a new set of less colorful pictures of various sensors I have lying around. I don't think any of them are great, they're just what I can make myself. Includes some duplicates. Chop the ones you don't like, or substitute with better ones from the archives as you wish.

 

2. I revised this to "There's a sample error of maybe two meters; furthermore, the deviation is influenced by various factors and thus is far from predictable." Does that sound OK?

8. I like the changes you made for this one. Call it done.

I will have Kate look at the photos, and then we'll flag this as ready for publication.

 

Hi @KJ6EAD

We had a chat on our end regarding your concerns about phrasing, colloquialisms, etc. We'll certainly keep these in mind when we look at future articles. At the same time, however, we try very hard not to smother out an individual writer's tone and voice. It can be difficult to strike a balance between editing for clarity and editing for voice, but we'll keep trying.

Thank you so much for taking part in these conversations. We really appreciate your time and input.