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Step 4


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Building North Paw V1.0
Step 4: Final Assembly

Back to step 3: DisplayBack to step 0: Overview

In this, the final step, you’ll stuff the motor array into the armature, position the controller and battery onto the exterior of the armature, and hook them all on up together.

Supplies (incl. in kit / made by you already)

  • Completed North Paw V1.0 board in enclosure
  • Battery enclosure
  • Pager motor array on Veltex backing
  • Ultra-chic North Paw anklet

Tools (not incl.)

  • Pliers
  • A second pair of pliers (highly recommended)
  • — or —
  • A vise (insted of the two pairs of pliers)
  • 3 x AAA batteries

Take note of the position of the slit cut into the armature. Unzip the anklet and insert the pager motor array. The thickest part of the ribbon cable should be towards the end of the anklet with the slit. Make sure the pager motors face the soft silver fabric – that’s the side of the anklet that is held against your skin and we want the motors right on you! As the zipper is slightly shorter than the whole anklet, you may need to pinch from the outside and wiggle the last motor up to the edge.
Once the motor array is snug, fold over the left-over length of ribbon cable and pull it through the slit. Now affix the controller to the anklet such that the edge is 0.5 inches from the slit.

This part is a important and seems to be a little tricky to explain, so here goes: the controller is fairly stupid. All it know is what the compass chip tells it, it doesn’t know anything about where the motors are relative to itself. So, if it thinks it’s pointing North, it will turn on motor number 1, regardless of where motor number one is. If it think it’s pointing South, it will turn on number 5, and so on. The orientation of the motors and the controller relative to each other is vital, as you’ll see later on during the calibration phase.

Place the crimp with the notch up and move it to the best position for it plug into the controller. If you look closely you can see the teeth that will be grabbing onto the strands of the ribbon cable and making electrical connections. Make sure these all line up with the strands properly.
The easiest way to crimp is to hold both sides with pairs of needle nose pliers and squeeze them at the same time. It may take a fair amount of force and the crimp may not snap perfectly; that’s ok. If it’s holding, it’s in well enough and you can squeeze laterally to get the ends to snap. Another way to do this is to set the crimp and cable just right in a vise and turn it shut.
If you have much ribbon cable left over, trim it with some scissors then go ahead and plug the display into the controller. Congrats, you should be done building! Slowly turn the North Paw in a circle, and make sure that all eight motors are connected. Put it on and see how it feels!
The final step in this process is the calibration phase. Grab a normal compass, or go somewhere that you know exactly where North is. Put your North Paw on, and turn around slowly. You’ll notice that the motors will sometimes point in different directions. This is because in step 3 you spaced the motors out evenly, but actually this would only work if your ankle was perfectly cylindrical. It’s not, so you now need to move the motors around until they all point to the same North. It’s best to do this one motor at a time. Find a motor that points the same way as your compass does, and then turn until your North Paw changes to another motor. Feel and remember the amount at which that motor is pointing away from North. Take off your North Paw, unzip the motors, and move that motor over by the amount you felt. Put it back on, and repeat, this step will only work after a bit of trial and error. While you do this, be careful not to bend you solder joints too much as they can break.

Looking at the diagram to the left might give you a better spatial understanding of why the motors need to be spaced differently depending on each individual ankle’s unique shape. Note the length of the arcs between the yellow dots, that’s the space that should be between the motors those dots represent. You should also consider that spacing the motors in this way means that if you change ankles, or wear the North Paw turned from how you calibrated it, then it will no longer be perfectly calibrated. Keep that in mind!

Back to step 3: DisplayBack to step 0: Overview


North Paw V1.0, for help contact eric@sensebridge.net

First published July, 2009


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