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BEAM colony trails idea

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  • rlnansel@...
    Here s an idea I ve been toying with: magnetic line following Herbie-esque rovers that use a combination of mono and stereo cassette tape heads to create and
    Message 1 of 6 , Jun 2, 2014

      Here's an idea I've been toying with: magnetic line following Herbie-esque rovers that use a combination of mono and stereo cassette tape heads to create and follow magnetically defined paths on a magnetic surface. In scouting mode -- looking for energy hotspots, say -- the Herbie follows its light sensors while simultaneously laying down a full-width mono track of pulses related to its mission. The idea is to get a constant linear spacing between pulses so the number of pulses per wheel revolution stays more or less the same. A slower Herbie would expect to "read" lower pulse frequencies and vice versa.


      In tracking mode the stereo head provides left & right signals to follow an existing magnetic path. A scout would switch to this mode after executing a 180 degree turn. The scout would have recorded bursts of, say, two pulses with a delay of twenty pulse times between bursts on the outbound trip. On return from a successful foraging mission, the scout would read and rewrite each pulse successively, then lay down an additional pulse to reinforce the trail. Every successful trip thus adds a new pulse to the bursts along the path until the pulse bursts merge to one continuous pulse train.


      On failed trips (where energy was no longer available at the terminus) the Herbie does the opposite by not rewriting the last pulse, thus allowing the path to decay after a number of such trips have been made.


      One problem I haven't figured an easy solution for is what sort of magnetic material to use for the  running surface. I 'spose I could glue down stripes of VHS tape side by side on a substrate, but that seems like a pain.


      -Bobby

       

    • John Floren
      Well, as far as I know regular magtape, hard disks, floppies etc. just use ferrous oxide. You might be able to mix ferrous oxide powder into paint and apply it
      Message 2 of 6 , Jun 2, 2014
        Well, as far as I know regular magtape, hard disks, floppies etc. just use ferrous oxide. You might be able to mix ferrous oxide powder into paint and apply it to a surface, or you *might* be able to use that paint magnets will stick to... I'm assuming it uses some sort of metal content to be magnet-attracting while not actually magnetic itself. You could build a robot and test with strips of taped-down VHS tape, then once you've verified operation, try it on a sheet of cardboard painted with the stuff.

        Neat idea!


        john


        On Mon, Jun 2, 2014 at 7:12 PM, rlnansel@... [beam] <beam@yahoogroups.com> wrote:
         

        Here's an idea I've been toying with: magnetic line following Herbie-esque rovers that use a combination of mono and stereo cassette tape heads to create and follow magnetically defined paths on a magnetic surface. In scouting mode -- looking for energy hotspots, say -- the Herbie follows its light sensors while simultaneously laying down a full-width mono track of pulses related to its mission. The idea is to get a constant linear spacing between pulses so the number of pulses per wheel revolution stays more or less the same. A slower Herbie would expect to "read" lower pulse frequencies and vice versa.


        In tracking mode the stereo head provides left & right signals to follow an existing magnetic path. A scout would switch to this mode after executing a 180 degree turn. The scout would have recorded bursts of, say, two pulses with a delay of twenty pulse times between bursts on the outbound trip. On return from a successful foraging mission, the scout would read and rewrite each pulse successively, then lay down an additional pulse to reinforce the trail. Every successful trip thus adds a new pulse to the bursts along the path until the pulse bursts merge to one continuous pulse train.


        On failed trips (where energy was no longer available at the terminus) the Herbie does the opposite by not rewriting the last pulse, thus allowing the path to decay after a number of such trips have been made.


        One problem I haven't figured an easy solution for is what sort of magnetic material to use for the  running surface. I 'spose I could glue down stripes of VHS tape side by side on a substrate, but that seems like a pain.


        -Bobby

         


      • rlnansel@...
        Conceptually, nothing would beat the simplicity of just sprinkling rouge on a sticky surface. But getting an even, smooth layer with no clumps might be quite
        Message 3 of 6 , Jun 2, 2014
          Conceptually, nothing would beat the simplicity of just sprinkling rouge on a sticky surface. But getting an even, smooth layer with no clumps might be quite difficult. Then, too, as the inventors of the first video recorder in the 19050s discovered, iron oxide is quite an efficient abrasive, so much so that their video heads only lasted a few plays with their very first tape surface formulations which lacked efficient glazing and lubrication layers. Still, if a typical robot moves about the same linear speed range as cassettes and microcassettes (roughly 1 to 4 cm/s), wear wouldn't be as acute a problem as with video recording. (VCR helical scan gives an effective linear speed of nearly 6 m/s, more than a hundred times faster than audio tape speeds.)

          Seems to me Tim Hunkin did something of this sort in one of his Secret Life of Machines videos, where he managed to sprinkle rust powder onto the sticky side of a strip of scotch tape. He was frankly amazed to get any sound at all from his jerry-rigged setup, and it was definitely not hi-fi. 

          The magnetic paint idea might work. Has anybody used this stuff? How smooth a finish can it produce?

          -Bobby
        • rlnansel@...
          Here are some numbers for mag tracking Herbies: Cassette tape is 0.144—0.150” (3.66mm) wide. Mono tape heads record tracks 0.060” (1.52mm) wide, with a
          Message 4 of 6 , Jun 2, 2014

            Here are some numbers for mag tracking Herbies:


            Cassette tape is 0.144—0.150” (3.66mm) wide.


            Mono tape heads record tracks 0.060” (1.52mm) wide, with a centre guard band of 0.027” (0.69mm) width. This gives two tracks on a mono tape, one for each “side”. 


            Stereo tape head tracks are reduced to 0.0235” (0.597mm) wide, with a pair guard band 0.012” (0.30mm) wide between L & R tracks. Similar to the mono format, there are two “sides” on which stereo tracks can be read, so there is another guard band in the centre 0.0275” (0.699mm) wide to separate the two sets of stereo tracks. Note that adding up the widths of two track with the pair guard band width gives a total width of 0.59” (1.50mm), just a bit narrower than a mono track.


            A mag tracker always records with a mono head (MH) and reads back track signals with a stereo head (SH). 


            Now, if the mag tracker SH is travelling centred and aligned on a previously laid mono track, both L and R elements of SH should see roughly the same signal. If SH is centred but the direction of travel deviates slightly from the track — azimuth error — L & R should still produce similar signal levels relative to each other. After further travel in this direction one of the SH pickups will eventually leave the mono track while the other pickup will remain on the track, thus creating an imbalance in the signal levels. It’s this which a mag tracker uses to servo back toward alignment with the mono track.


            I’m supposing that we can use saturation recording so we won’t have to muck around with an ultrasonic carrier. Since each pulse would then consists of both a positive and a negative going spike, the read circuit needs some means of clipping or maybe just ignoring negative polarity spikes.


            -Bobby

          • rlnansel@...
            A correction about the effect of stereo head (SH) azimuth error on the readback of a mono track. I stated that as long as the SH was centred in the mono track
            Message 5 of 6 , Jun 3, 2014
              A correction about the effect of stereo head (SH) azimuth error on the readback of a mono track. I stated that as long as the SH was centred in the mono track that the signals for L and R transducers of SH would be the same. This would be true if the SH could pick up DC magnetisation values from the tape and if the mono track itself was magnetised in a continuous orientation. Neither of these things is true, however.

              Because the mono head (MH) is writing a single pulses the width of the head, an azimuth error on the Herbie's heading on the track results in a phase difference between the signals picked up by L and R. When RH isn't centred on the mono track there will also be an amplitude difference between L & R.

              This is good news, because servoing on phase as well as amplitude will give a Herbie mag tracker more precise way of following the mag track. Small heading deviations result in a phase error signal, but larger heading errors give an amplitude error signal, too.

              -Bobby

            • rlnansel@...
              I ve located a supplier of magnetic latex paint http://www.visualmagnetics.com/content/files/datasheets/VM_Activewall_100313.pdf. The company is Visual
              Message 6 of 6 , Jun 7, 2014
                I've located a supplier of magnetic latex paintThe company is Visual Magnetics, and they make a number of magnetic products, including laser-printable polyester sheets backed with a thin magnetised layer of what I believe is essentially refrigerator magnet material (viz, iron oxide in polymer binder).

                "ActiveWall Micro-iron Latex Primer" is the paint, and I'm supposing it comes not magnetised because it's just to make walls ferromagnetic enough that magnetised graphic sheets will stick to them. It's a bit pricey at $38AU per litre, but that should cover about 2.5 m**2. The only question I have is which iron oxide they use in their mix, because only iron (III) oxide has the right coercivity and remanence properties to record on magnetically. The primer is black, so I suspect it may be iron (I) oxide, and that won't work.

                If the paint won't work, though, I could get a reel of 2-inch studio mastering tape on ebay for a reasonable price (at least before shipping). It would be a much easier process to make a large running surface using 2-inch wide strips glued down side by side than using 1/2-inch video tape.

                -Bobby
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