Based on other ideas, this is a project to create a modular machine to be used for drawing texts on the floor.

Requirements:

1. Simple, cheap, easy to implement and reproduced.
2. modular, fits different types of carts.
3. Should have modules to allow painting using water, paint or sand.

Code:

https://github.com/amirv/waterwriter

High level design:

First design is to use something like that:

Inside it there will be a pressure tank like this (or two of them):

And a micro-controller to control 8 valves and a rotary encoder.

Using the rotary encoder which count the wheel rotations the micro-controller can sense the distance the cart moved.

According to the distance and text fed to the micro, 8 valves will be timed to print the text on the ground.

The painting module should be modular, and can paint using water, paint or sand.

See for example this:

The valves could be bought, like this:

Or printed like here:

Another nice option for a valve using a servo here:

Some links:

https://www.thingiverse.com/thing:2253252

https://www.thingiverse.com/thing:3307864 :