Part 2: Speed Writer
Speed writter races around with a spring loaded piece of jumbo chalk writting words. Using a hacked "Rebound" RC car for the body and an Arduino Nano for the brains.
Part 1 of this robot page is my tip/walkthrough on hacking the Rebound for robot use. This lets me use the original PCB for motor control and left me with a clean chassis to build upon.
Since this photo was taken I have made several modifications to reduce noise and am now deciding what sensors to uses. For now I am trying 2x IR sensors.
Hopefully these will stop speed writter crashing into anything while writing. They are just simple digital sensors and are being used like invisible antenna. They have a pot on the back where you can set their sensitivity/range. As the robot is very quick I've set them to their maximum range of 80cm in hopes the robot will detect an object in time to turn before crashing. Fortunately the rebound dual "H" bridge has electronic braking :D
Ok, I had some trouble with power dropping when both motors started suddenly or changed directions. Using a low dropout regulator instead of the 7805 made a big improvement. The IR sensors still give a brief false reading due to noise when the power spikes so I will use a simple RC filter to eliminate spurious signals.
I wanted to use "Jumbo Chalk" on the back of this but I couldn't find any locally so I decided to tape 6 smaller sticks together. Remembering too late that chalk is weak and brittle.
Guess I'll have to chalk that up to experience :P
Using some mecano from the original "Mr. Tidy" arm and a caterpillar antenna spring I made a new spring loaded arm to hold the chalk. The spring is mounted in such a way that it holds the arm up when not in use and applies gentle pressure to the chalk when the arm is down.
Now I just need to program it to write "LMR".