Development of the water tank, pump and feed mechanism

 
For
      a mobile robot to water plants at various locations around the
      home, it must carry and maintain a tank of water which is fills,
      travels with to the plants and then dispenses. And when it is
      low, it must refill as needed. Here we are going to show you
      this weekends progress on this facet of CBOT, and some testing
      of the water pump in action!
 

      
Left: Here
      is the water tank (Tupperware) on the bench to show its internal
      sensor. This consists of a flat plate with electrical contacts
      at various levels in the tub, which mark four different levels.
      As the water touches each set of contacts, the circuitry detects
      the change in resistance and indicates the water depth with a
      LED lamp, and sends a TTL level to the micro controller so it
      knows where the water level is at all times. Now it doesn't have
      to know EVERY water level there is, just when we are at four
      key positions. A huge cup of water is waiting on the left to
      be dumped in. The tub is 8 inches across and 4 inches deep.
 

      

      
Left: Schematic
      of the water sensor. CMOS logic gates are used to detect the
      change in conductivity and put out a 0 - 5v level for each step.

      
Below:

      
Water at several
      steps as I fill the tub, showing the LED lamps lighting as the
      water level gets higher. There are four levels indicated - Too
      Low where the pump water intake occurs, Fill is the low point
      normally, Full is the maximum when full, and Over full is way
      too high and will make a mess.




      
Left: Now
      mounted on the side of the tub, the circuit board is ready for
      action. Wires send the signals to the micro controller on the
      top deck.
 

      
Left: The
      latest view shows the water tubing coming out of the pump, through
      the lid and on to the post mount on the right side. A quarter
      inch mast will run the tube up to the top.
 

      

      
Left: Well, this
      is the basic concept on how I plan to have the robot water the
      plants. There will be 2 - 4 planting trays exactly like the one
      here, with funnels mounted in two or three places on each. The
      robot stops at each funnel and turns on the pump. The funnels
      connect to a tubing distribution system for each plant that carries
      the water right to the base of the plant. This way the robot
      does not have to be dangerously close to the delicate plant.
      Now the cool part - each funnel will contain watering instructions
      as to how long to run the pump so each plant gets the exact amount
      of moisture daily. I will determine this for the week and place
      a color chip at the funnel. A small camera with a color sensor
      will read each color at the funnels and send the amount of water
      I have indicated. So like red is pump for say 1 second, and blue
      for three, etc. (wait till you see the color sensor, its totally
      cool!)

      
The end of the
      tube will be attached to a curved piece, which I dont have here
      yet!



      
Left: Setup
      to see how much water will squirt out when I fire up the pump!
      Here Im manually filling the tank. The plan will be the docking
      station will do this automatically each time the robot docks
      for the night.
 

      

      
Left: And - Blastoff!
      with 12 volts on the pump motor in the tub, we get a very nice
      stream.

      
The next steps
      are to now automatically fill the water tank. The robot will
      actually do this by monitoring its water levels and running the
      fill pump on the dock by itself. Now that will be a trick...



      
Interested in learning
      more on the development of this robot? Here are previous uploads:

      
Previous Articles
1. Plant watering sensors
2. Cbot basic concepts and project definition
3.  Docking sensor, battery charging and FSM explained

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