another iteration of the bot

I did a bunch of hardware modifications to my bot over the weekend to make it more sturdy and to get rid of most of the loosely connected wires and the separate proto board. This is what the current iteration looks like:

The main changes are:

  • 5Ah Li-ion battery replaced with two 4.6Ah NiMH batteries connected in parallel because for me the relative safety of the NiMH outweighs the capacity/weight gains of the Lithium based chemistries. I really don’t want to worry about my house burning down while charging the battery packs.
  • Replaced the Wifi dongle with a far smaller one. The new dongle is using Realtek 8192cu chipset which isn’t supported out of the box as well as the old Atheros based dongle was but I think I got it working reasonably well in the end.
  • Replaced the older generation BeagleBone with Beagle Bone Black (BBB).
  • Moved the bidirectional level shifter that is used for serial communication between the Wild Thumper Controller and BBB from separate proto board to BeagleBone proto cape.
  • Changed BBB’s power supply from 1.5A Recom 78b5.0-1.5 to 3A BEC. This change was actually done because the 3A BEC comes in a nice discreet package which is already more or less protected from the environment and having more power available is just a nice side effect.

With that the platform is stable enough that I can actually concentrate on the navigation. On that front I set up an RTK-GPS solution with RTKLIB and couple of borrowed u-blox LEA-6T evaluation kits.
This is how my ad-hoc base station looks like:

This is what the signal levels look like in RTKNAVI:

To get a good set of waypoints for testing the robot I walked a couple of times up and down my driveway:
rtkplot showing me walking up and down the driveway

The yellow dots show the FLOAT solution and the green ones show where I had the FIX solution. Basically getting the FIX solution is more precise and means the calculations that RTKLIB does, lead to a single unambiguous solution at these points.

Zooming in we can see that the points from different times are at most about 20cm apart which is really good considering that I was just trying to walk in the track of the car wheel and certainly veered off a bit at times.
RTK solution closeup

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