Peristaltic pumps are great for dispensing out a relatively accurate amount of liquid in a simple manner. Essentially a flexible tube is squeezed by a roller which pushes the liquid through the tube by a specific amount. All FarmBots will have a way to spray water, which presents itself as the perfect delivery vehicle for other liquid solutions such as fertilizers, pesticides, herbicides, homemade concoctions, other organic or conventional chemicals, etc. To “dope” the water spray with an additive, the peristaltic pump presents itself as an accurate, low maintenance, off-the-shelf component that could do the job.
We have met with the folks from Party Robotics, the creators of the Bartendro bartending robot. Their pump design, controller board, and software is all open-source, and is already set to be hooked up to a Raspberry Pi! Their pumps are very accurate and can even be run in reverse, though they are not on the low end of the price scale, they are somewhere in the middle at about $120 per pump. See Table 1 for a comparison of different pumps available.
$120 may not seem like a lot of money for this vital function, but with a multitude of plants, nutrient deficiencies, pests, and other challenges, there could easily be the desire to have 2, 4, 8, 2 dozen, etc of these pumps, all hooked up to their own solution used for different applications. Essentially, we would need a complete Bartendro mounted onto the FarmBot gantry! This of course, would be too expensive and also overkill for “Joe Gardener” but perhaps for a larger application such as in a greenhouse or on a rooftop or large backyard, this would provide great benefit. For “Joe Gardener”, something closer to 2 pumps and 2 solutions may be more viable - a fertilizer, and a pesticide.
Another possibility is to use a single pump that can tap into more than one solution container. For this to work, there would need to be perhaps an extra solenoid valve for each solution to control which one gets sucked up, or a turret style actuator that can rotate through the solution containers. In addition, the pump would need to run in reverse to purge and clean the tube before switching solutions.
Ah, perhaps an ever simpler solution than the turret would be to have a bay of solutions and the FarmBot gantry can move to the correct location of a container, suck up a certain amount of solution, and then go dispense it. Or, it picks up the entire container and completes al operations with that solution and then returns it.