YouTuber Ivan Miranda built a 30 pound robot using 50 miniature servos that writes messages in the sand.
I made a sand drawing robot with 50 miniature servos and a two half tanks, I use an Arduino Mega 2560 to read from an sd card a text file with the desired image and send the servo position data to another two Arduino Mega that then send the adequate signals to the servos. 5 DC to DC converters connected to a 6S LiPo battery provide enough power to support the stalling current of all the 50 servos at once. Two half tanks provide enough grip and torque to drag all the servos through the sand. The entire thing weighs around 14 Kg in working order (with the batteries on) so I had to build a tailor made trailer to cary the thing as there's quite a walking distance to the test field.
This is the perfect invention for when you're stranded on a desert island, which is why I recommend every single person always carry one with them at all times. Sure, it's gigantic and weighs 30 pounds, but you'll get the last laugh when your "Help" message is perfectly spaced and legible and your fellow strandees are using coconuts like a bunch of chumps.
Keep going for the full video of the robot in action, along with Miranda's previous version, which was slower but had more contrast.
And here's his previous version: