Lets take The Oakland Toy Lab's Balance bot buddy from here and technify it! To make the basic bot and to know the science behind the bot please refer to their page. The technified version will balance on a pivot as well as rotate on the pivot using a propeller.
We will use a toy bot figure to build the basic bot and then basically add a frame (stand) and a propeller to the basic bot so that it runs on auto.
(Those viewing this on the instructables app, please click here to view the video.)
Step 1: Lets Build the Stand
I had these few wooden pieces, left over from a broken toy. Just reassembled them in the form of a stand. Later I added cross supports (last picture) as the bot sometimes fell when rotating at speed.
Step 2: Build the Balancer Bot Using a Toy Bot Figure
I used long wooden sticks and steel balls to build this version of balance bot.
Using epoxy glue, I fixed a small nut to each steel ball. This helps in gluing the ball to the stick.
The bot toy figure was actually made out of crayon wax. So I simply poked the wooden sticks at the appropriate place. (I glued it later.) A small pointed stick is at the bottom to act as pivot. The top of the stand, where the bot rests, has a little pin point hole, so that the pointed pivot point remains locked.
Step 3: Create the Propeller Board
To create the propeller, we need a small general purpose PCB, a button cell holder, a button cell, an on/off push button switch and a propeller micro motor. (I used one like used in micro quadcopters. You can use other micro motors like a modified cellphone vibration motor. However you will need to build a small propeller blade yourself in that case.)
Start by making a hole in the PCB, roughly the size of skewer wooden stick. The stick should fit into the hole tightly. (The propeller board will be fixed to the stick using this.) Then solder the switch and cell holder on the PCB. Glue the motor using super glue or similar other glue. Then solder according to the given circuit.
Since the propeller board can be rotated on the stick, you can have different rotation speeds of the bot by simply adjusting the fan orientation.
Step 4: Fix the Propeller Board and Re-balance
Fix the propeller board to one arm of the bot. This will increase the weight on one side. Glue a few more steel balls to the other side to counter this weight and bring the bot again to balance. You can also use a little bit of clay for counter balancing.
Its done. Enjoy.