In this section
      we will discuss one of the most important and often overlooked
      aspects of successfully docking your robot to the charging station:
      The Electrical Contacts. Sure enough, you now have the knowledge
      and programming skill to get that robot to recognize, drive to
      and make physical contact with the battery charger. But none
      of this is any good if you can't make a low resistance electrical
      circuit with the charging plates. Here, we will go over several
      different styles of charging contacts, and the methods we connect
      to them.

      
Hoops,
      Rings and Curved Contacts

      

        

          
 
          

            
Docking Cylinder 

            
This relatively
            straightforward connection technique uses a cylinder as a docking
            base, with the contacts on each side. Between the contacts, the
            beacon guides the robot in, and the whiskers on the robot touch
            the sides of the cylinder, and make electrical contact. You can
            make the cylinder out of any nonconductive material, as long
            as it is weighted to not move easily. The contacts can be brass,
            copper or aluminum foil tape strips, and will fit the curve of
            the cylinder.

            
On the robot, the
            "feelers" that will nest on both sides of the can are
            made from large diameter guitar strings, the brass kind that
            wrap around a music wire core. They can be easily soldered to
            and make very resilient touch sensors as well.
          
        
      

      

        

          

            
 "D"
            shaped curved straps

            
Another favorite
            of ours is using a pair of flexible brass straps, that are spaced
            at about an inch apart mounted to a flat vertical surface. When
            the robot connects, they bend and conform to the curved frontal
            contact on the robot. We tested this version first, and found
            it worked quite well.

            
On the robot, the
            front bumper is split into two contacts, one on top of the other
            spaced by an air gap. This will nest perfectly with the two curved
            straps on the charging base.
          
          
 
        
      

      
Flat Plates
 

            
 Flat Wall
            Plates

            
Another great favorite
            of ours, was this technique. Here, we once again use guitar strings
            on the robot as feelers and electrical contacts at the same time.
            The plate is two copper or brass flat surfaces, with a gap between
            for the IR beacon LED. The robot drives right into the plates
            and gets connected quite well, the resilient bending of the guitar
            strings for feelers makes a great contact brush.

            
We rather liked
            this one as well, but sometimes the robot would come in at too
            steep of an angle and miss the plates on one feeler.


      

        

          
 
          

            
 Upper Overhang
            Contact

            
This design is
            rather tolerant of poor alignment and can also use the guitar
            strings for contacts on the top of the robot. The top plate under
            the overhang is really two copper plates in which the robot drags
            its feelers over when it drives underneath. This creates a decent
            electrical connection, and protects the robot as well from dust
            and from being a trip hazard at night.

            
One robot we so
            equipped looked quite "Spacey" with the two antennas
            on top, and yet they were not for decoration as most are, but
            were essential electrical contact mechanisms.
          
        
      

      
Inductively Coupled
 

            
 Inductive
            Coil Charging

            
One reader on Robots.net
            suggested to me this method, which he is currently working on
            for his own robot. The robot drives in over a puck shaped disk,
            which contains the lower active air gap transformer. In the bottom
            of the robot is the upper air gap coil, and when brought in proximity
            or actually slid over each other would be better, you get sufficient
            charging current to work with. One great advantage of this method
            is there is no electrical contacts and no chance of accidental
            shorts.


Underside Contacts
 

            
 Drive over
            Contacts

            
This is the type
            we finally used a few years ago on PAAMI, our priority arbitration
            robot. The base has two tight springs sticking straight up with
            chrome balls on them for contactors. The bottom of the robot
            is two flat plates which slide over the balls to make a nice
            spring loaded contact. Other variations include brass buttons,
            brass levers hinged on one end, and yes even steel wool pad will
            work fine here.


      

        

          
 
          

            
 Conductive
            Wheels

            
The idea here is
            to have the robot simply drive over some live electrical plates
            and use the wheels to conduct the power into the internal charger.
            In practice this sounds great, but is very difficult to pull
            off. All metal wheels do not fare well in a household or office
            for one, and pick up a coating of non conductive dirt in no time.
            Also, it is not easy to link the charger to the axles of the
            wheels. Some have tried conductive foam wheels, but that wont
            last very long. Perhaps one way is with contacts that drop down
            when the robot strikes the vertical surface of the charger. A
            lever would push and drop the brass contacts down to the surface,
            retracting them when the robot backs off the charger.
          
        
      


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