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Beach Detecting Rover project

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  • #76
    @Paul23: I have 4 driven motors with wheels, and 2 non-driven wheels with encoders. This should allow pretty decent dead reckoning. I want to try two things. 1st method: I will get a very accurate initial reading at base control. Base control has GPS not moving. Long averaging. As I move the rover, I'm updating my positioning via dead reckoning. 2nd method: I will pause the rover for every 24 scans of the boom, updating position. Once scans are done I move the rover again via dead reckoning to next spot (12" later), process starts over. I want to see how these two methods compare.

    @Tepco: I could use this for mine detection. That's not what I'm shooting for though. I am building this platform to test both my robotics experiments, and my MD hobby. This rover is semi-automated. Not fully automated. Semi automated makes remote control easier, but still leaves major control in my hands. Sweeping will be automated. Rover movement except for turns will be automated. A turn can even be semi automated. My perspective from a hundred feet away will be skewed. The rover will turn the precise amount to ready itself for another pass. I will simply hit a single button, rather than steering manually. Same thing goes for movement. I will have a button for "shift +" or "shift -". This will turn the rover 45deg move forward a bit, then turn rover back 45 deg. All with a single button click. This is semi automated. You DONT want fully automated. Too many variables to control, and it won't work, since over time those unknown variables will stack until it's completely out of whack. Keep in mind, I will have a map on my operator station of the rover's movement track. I'll see my scans and the boom sweep. The boom sweep area will be color coded one color, and the rover movement track will be another.

    Of course, if I want to steer or turn manually, I will be able to do so if desired.

    Hopefully, the MD portion, via the small particle gold detecting I'm planning on doing, will pay for the project. It's not necessary though. Just doing this to have fun. I've been building machines like this for years at my regular job, and I want to do something on my own with my own budget. The sky's the limit with a $500K+ budget. Last system I built, for around $1M saved a customer about $30M. This technology is very marketable in certain industries.

    @Midas: That's what I'm thinking GPS method #2 will get me.

    @Davor: You know that's actually not a bad idea. The Phidget GPS uses an external antenna, I may be able to exchange for one better suited.

    Here is my take on GPS. It doesn't have to be perfect. The repeatability I will have with GPS couple with dead reckoning off of non-slipping wheels is the main thing. It will allow me to see big patterns in a scan field not possible with single point measuring. As long as the targets are referenced off one point, that's my main goal. That will allow me to see the invisible dry wash with the gold targets along its path. Stuff just not possible with hand digging.

    My MD coil will also make a big difference in my opinion. By doing little bitty scans and not missing a square centimeter, I bet you I'll be able to find stuff that is missed. I bet I could even go to a known gold location and find stuff that has been missed a hundred times.

    As to my part receipt progress. I received in my last 3 motor amplifiers for the main wheels. I also received my rotation axis with motor. I'm still waiting on my 24V power supplies from Hong Kong, and my 1.85KW generator to come in.

    Started laying out the frame this weekend. I built a raised work bench approx 4ft x 8ft and 30" high for laying out the frame.

    I made good progress on the frame. I have the two sections cleaned up quite a bit, and have the connection bar ready to couple on both sides.

    Attached are pics of the frame and work bench.
    Attached Files

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    • #77
      pololu amp test

      Ok. Here is a test I did with the Pololu 24V23 amplifier that will be running the wheelchair motors. I ramped from 0 to 100% positive, back down to 0, then 0 to 100% negative.

      The power supply is a 120W power supply. The actual power supply these motors will have is a 350W power supply.

      Here is the link:

      http://www.youtube.com/watch?v=bVN7-...ature=youtu.be

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      • #78
        I'm not sure how much the base station will help in that implementation. My (admittedly limited, never tried it in any really open area) experience is that you can have two identical gps modules sitting right next to each other and they will still quite likely lock onto a different set of satellites. As a result they pretty much wander independently. The conclusion I came to was that a true differential GPS really needs individual raw satellite data from the base and rover which then needs to be processed together to give the corrected position. If I remember rightly I did find a module that offered the raw data but it was a lot more expensive and didn't think all processing was going to be a walk in the park either. So I gave up...

        Midas

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        • #79
          I wouldn't give this GPS precision too much worries. Using WAAS or any other wide area augmentation at hand, which is very common nowadays, and having a rover roaming outdoors, with no trees or buildings to screw readings, and averaging results by means of inertia of the rover itself - I'd say it will work just fine.

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          • #80
            motor testing continued

            I recieved my 24V, 14A power supplies today. They work well. Nice stable output, relatively small housing, etc.

            I wanted to do a long test today with the whole motor train: 24V/14A PS, Wheelchair motor, 24V23 amplifier and run it for a couple hours, monitoring temp, current, etc.

            Well, about 30minutes into my test, I start to notice a burnt smell (yes, that one). I had earlier felt everything, and it was cool, motor, amp, PS. I couldn't figure out where the smell was from. Then I notice the smoke curling out of the brake on the rear of the motor.

            Lo and behold. Apparently the brake on these motors is 12v. Not 24V like the motor. I go to check on a replacement brake. Keep in mind I got these motors for about $100 for a pair on Ebay. The brake alone is $203 new. Ouch. The motor is $1207 new. Each. Wow. So, the lesson here is to read the spec sheet, BEFORE running a 3 hour test.

            Oh, well. I guess I'll be ordering another whole motor assembly...

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            • #81
              That's a shame.

              Do you need brakes on all four?

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              • #82
                No actually I've considered not using them actually. With the load of the rover, it should be pretty hard to backdrive four motors anyways. Removing the brakes could also let me mount encoders on the motors also. It would make positioning somewhat easier also. Not a big deal really, just a good reminder to be careful. Especially on a shoestring budget like I am.

                What I can't believe though is the cost of the motors new. If I was buying these motors new it would cost almost $5000 for four motors new.

                I know my extruded aluminum framing was a couple thousand, but I didn't expect the motors to be so much. Thank goodness for Ebay! I'm not sure this rover would be achievable without the surplus market. A new build using new parts would easily exceed $10k or $12k. That's not even counting what the software development cost would be.

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                • #83
                  Doesn't a shorted motor work as a brake

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                  • #84
                    It will, but whit break torque not exceeding one in normal (drive) condition, more or less, may not be sufficient in some situations. Heavy machine can be accelerated slowly, but if it needs to stop rapidly, significant (kinetic) energy must be wasted somewhere quickly, then, without some mechanical means, motor itself will not be able to do that, not only shorted but even using reverse drive (drive power control is current limited).

                    12K$ for this project, without Ebay, is very optimistic!

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                    • #85
                      more testing done

                      Ok. Got some more pieces tested today. I got some base functionality tested from the software side of things. I wrote a test xbox controller client for the laptop and the rover PC pololu server running. The test consisted of the xbox controller interfaced to my laptop interfaced to the rover PC controlling the motor amp driving the wheelchair motor. I was able to drive the motor forward and backward using the left xbox thumbstick. This was over the network using the wireless access point. At the same time I had the rover PC screen displayed via a VNC window. The motor was quite controllable.

                      Also tested today was the basic code for the boom arm scanner amplifier which will use the Phidget motor controller. That code worked well also. I even had time to get the data logging code working.

                      More later!

                      I'll get a link for the test posted tomorrow...

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                      • #86
                        Chassis almost prepped and other things..

                        OK, Been working on the chassis parts lately. I almost have all of the salvaged 80/20 extruded aluminum torn down, cleaned, and ready for assembly into a chassis. I received the generator yesterday too, yay! That's the last major piece I've been waiting on, so from here on its build, build, build.

                        Attached is a screen capture of the cleaned up and disassembled 80/20 aluminum.

                        Been working on a project at work this week. It was a quick turn around 2 axis measuring application. The great thing about it it, is it gave me another good run at the Flowstone software. It looks like that will indeed be promising as a GUI and Phidget interface. Got to try out some features I hadn't before, namely data logging and multiple Phidget Axis control. Learned some helpful stuff.

                        I have a screen capture of that GUI just to show an example of what Flowstone can do.

                        I should have the aluminum finished up tomorrow...
                        Attached Files

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                        • #87
                          links to motor testing videos

                          Here are the links I promised a couple days ago for the motor testing on the Rover. The wheelchair motor is still connected to the Pololu 24V23 amplifier, interfaced to the PC via USB serial COM port.

                          Part1: Original test of wheelchair motor with Pololu 24V23 amplifier. Uses Pololu configuration software for this test.

                          http://www.youtube.com/watch?v=bVN7-...hannel&list=UL

                          Part2: Xbox controller driving Pololu 24V23 amplifier locally.

                          http://www.youtube.com/watch?v=yWIeZ...ature=youtu.be

                          Part3: Xbox controller read interfaced to a client on a remote computer wirelessly connected to a server on a local computer interfaced to the Pololu 24V23.

                          http://www.youtube.com/watch?v=we-Qr...ature=youtu.be

                          Part4: Same as Part3, but illustrating the VNC remote viewing of the local computer onto the remote computer.

                          http://www.youtube.com/watch?v=brFuH...ature=youtu.be

                          Sorry bout the video quality. I'm not the greatest videographer by any means, but hopefully it will be of interest to someone...

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                          • #88
                            Your making good progress.

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                            • #89
                              really cool screen

                              I just scored a couple of these for the rover.

                              http://www.mimomonitors.com/

                              I plan on having one in the controls enclosure directly on the rover as a local HMI screen for setup, debugging, etc.

                              One thing I really like about these. They are USB interfaced and powered! No VGA, No DVI. Windows sees it as a standard DisplayLink monitor.

                              Anyone out there working on a PC based Metal Detector? Here is an excellent little HMI touch screen for your PC.

                              The display is pretty darn good, and the touch screen isn't too bad also.

                              Not sure about direct sunlight readability. Its probably pretty poor on that front, but its an impressive little screen. Wouldn't pay list for them, but then this one was pretty cheap...

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                              • #90
                                Operator Station

                                Using those LCD screens, here is what I will try for the operator Station.

                                Keep in mind, the Flowstone can create nice little applications that I can scale to fit nicely into each of these screens.

                                I will use 4 of these screens for the Operator Station, and 1 in the Rover for a diagnostic display.

                                The key to this configuration is the USB interface. Multiple displays can be interfaced to the same computer. Tonight, I will see if I can indeed run 4 screens on one laptop. Obviously, I will be using a powered USB hub for this test.
                                Attached Files

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