mathy chats

@robotbuilder

I think any discussion of math should be restricted to the thread where the electronic or circuit problem is presented.

If there's a question about, say, calculations of impedance, then that should be given in the thread which expresses a problem with such calculation.

What might be handy is a reference link which contains commonly used formulae such as the calculations derived from Ohm's law, impedance, and so on. This could provide a one-stop-shopping source to help people find the formula they need.

@will 

 Sure.  Often the discussions end up as a continuation of an introduction in the introduce yourself section and then are lost forever.

What might be handy is a reference link which contains commonly used formulae...

When I was learning electronics I had all that stuff on charts on the wall that I could reference at a glance.

When I started with the Arduino and Raspberry PI I did the same thing with pinouts and all the details for using the sensors and so on.  All the basic stuff on which everything is built.

I can't attach them here because they are propriety property from actual teach yourself books.

One problem I keep backing away from is how to efficiently represent maps that a mobile robot can update and reference over time.  Is this a mathy problem?

@elvendecker Do you mean as in google maps giving you directions like turn left here? That is a software construct, basically a tree. There is likely a lot of samples etc on the web. If you mean displaying maps, then that is a lot of math but there are probably libraries for it. Also check if google has free api's.

@zander I'm thinking more of how to represent my backyard, or my living room.  A good representation (map) should be easy for the robot to create and modify, as well as easy to query.  Minecraft does a great job of this, but even though it runs on a raspberry pi, I'm a little intimidated by creating a high fidelity interface where my robot would create and interact with a Minecraft representation of the real world in which it finds itself. Is there anything lighter weight that might work purely in 2D?  Or do I submerge myself for a few months trying to figure out the Minecraft connection?

Mapping the Real World into Minecraft

The software that does the work

Linking MInecraft with reality

Demo video - throw a switch in Minecraft, turn on an actual light.

@elvendecker Ah, I don't know anything about minecraft other than it's some sort of game. If there is some sort of map engine you have free access to then that sounds like a good idea. Since I have no clue I will just wish you good luck.

@zander, @byron, Thanks.  It's worth checking out the video.  It shows a real-life robot turning on lights within the game, and vice versa.  So the Minecraft "game" would become the user interface for the IOT in your home.  Or becomes my virtual backyard where my robot plans to chase rabbits.

Posted by: @elvendecker

becomes my virtual backyard where my robot plans to chase rabbits.

Its an interesting though about mapping a virtual backyard, though at the moment I'm looking at using the aerial view my backyard from google maps.  The desire is to create a route for a bot to follow from the lat and lon as found from the Google maps and to input this into the bot navigation system.

Of course this has already been achieved with the likes of ArduPilot mission planner or the like.  The mission planner is Windows based and its more convenient to use my mac so I've not played with it yet. At the moment I'm looking at a making use of a real simple manual use of Google maps to pick up the waypoints lat and lon and feeding that into the bot control so as to follow this rout.

With simple GPS then the  GPS lat and lon can be 2 to 5 meters adrift.  Using RTK-GPS this can come down a couple of centimetres.  

I think I will be ok with an accuracy of < 500 cm.  What I don't know is how constant the inaccurate normal GPS coordinates are to the Google coordinates. So if, in my location, the GPS is, say, a near enough 3 meter distance to the SW of the Google coordinates, and this was a  constant for all the Google waypoint coordinates I plot, then that would be good enough for my navigation purposes.  

However, my readings lead me to think that the GPS coordinates will drift over time.  Maybe this too can be compensated for with another GPS unit located at stationary location (getting similar to RTK-GPS) but I don't know if two GPS units, of the sort one buys for hobby use, will even give consistent results with each other in the same spot at the same time.  (theres got to be a good reason for developing the RTK-GPS ).  But some experiment will see how consistency these GPS sensors are to each other and just how inaccurate they are in my location.  It may be good enough for my purposes,  I shall have to see what results I get.

When I get to that point I may turn to looking at the possibly of creating a virtual map, but I see problems as I'm not sure how, given my bot would initially range over a field of a couple of acres, it would locate exactly where it was currently situated in the virtual world.  The field boundaries that a lidar would locate would just be a hedge and would be out of range in the middle of the field.

@byron If you want to use that windows softwrae but don't want to install bootcamp or Parallels, look into codeweaver. I have used it to make a few non-supported even windows apps work.

@byron I forgot to mention, the standard GPS are off by a few meters intentionally and I would not be surprised if each unit is different. For your application you need a few cm's accuracy soooooo. The really accurate types are very expensive IIRC.

@byron I had originally given some thought to GPS, but because I have a small suburban yard, normal GPS resolution won't be good enough for my garden "features".  Here is a Google Map screen shot of my cell phone's GPS location while it's actually centered on the manhole cover pictured next to the road.  The error is about 20 feet.  And you're right, it "drifts" quite a bit.  I just needed to stand still to see the effect.

RTK-GPS is new to me, and it looks like it will simplify my future greatly. 🙂  Thank you!

My thought had been to create an editable polygon of GPS coordinates and have the robot refine the map over time.  Then I started to consider the GPS error which is larger than some of the garden nooks and cul-de-sacs.  Then I started looking for plan B.

I also considered something like an "invisible fence" used to keep pets in the yard.  The robot would be free to approach any rabbits (and turkeys and deer) in its field of view.  The only constraint would be to not come too close to the buried wire. This may be my ultimate solution as it doesn't require the robot to have much logic beyond traveling toward moving objects.

Rather than pulling the coordinates from Google or some other source, I think I would "teach" the corner points using the RTK-GPS and interpolate the rest.  Then at least we've eliminated some sources of error.

Thank you sir! I'll keep you advised.

Posted by: @elvendecker

RTK-GPS is new to me, and it looks like it will simplify my future greatly.

Posted by: @elvendecker

Thank you sir! I'll keep you advised.

Yes please, do keep me advised of any ventures you do with RTK-GPS. 👍   My finger has hovered over the buy button a couple of times in the past months / year(s), but as I was not ready to devote time to such a project I held off.  Also, @dronebot-workshop mentioned doing a video on this very topic, but at some point  I think it was mentioned there were difficulties in getting it to work ??  Maybe, Bill,  you can comment on the status of your efforts.

Also I rather doubt that I need just a couple of centimetres accuracy, more like up to 500 cm would suffice, so again I've been hesitating to purchase the rover and base station boards.  I think in some parts of the USA one can get free adjustment data via the internet and thus eliminate the need for ones own base station, but I can only find subscription based correction data services here in the UK necessitating the use of a personal base station as well as the rover board. (well thats my current understanding but maybe more study is required)

I expect I will faff around for a while with the normal GPS only to find it fails and then get to join you with a RTK-GPS solution.  And who knows it may come in handy should I need to accurately survey the positioning of a new potting shed. 😎 

Posted by: @byron

Also, @dronebot-workshop mentioned doing a video on this very topic, but at some point  I think it was mentioned there were difficulties in getting it to work ??  Maybe, Bill,  you can comment on the status of your efforts.

Actually I'm not having technical difficulties with GPS RTK, I ran into "climate difficulties".  By the time I got my base station working winter had arrived, and right now the backyard is full of snow and a lot of ice, as we had an ice storm yesterday. Plus, it's a balmy 17 below zero!

As someone who moved to Montreal from Hawaii, I'm quite averse to cold weather, and my rover's LiPo batteries aren't very fond of it either. GPS RTK work will resume when Spring has sprung, which according to our local groundhog will be late this year.  Can't do much with it here in the basement!

😎

Bill

Posted by: @dronebot-workshop

GPS RTK work will resume when Spring has sprung,

Thanks Bill, that surely give us something extra to look forward to besides the daffodils poking up 😀.  In the meanwhile keep snug an warm in your long johns and mittens.