Several years ago I discovered that most babies can be soothed more effectively by bouncing rather than rocking or swinging. I used to bounce my children to sleep when they were babies, while sitting on an exercise ball. This spurred ideas for an automatic baby bouncer.
The baby bouncer is a car seat suspended by springs from a frame. I used a hobby speed control powering a geared windshield wiper motor from a semi to provide the oscillating force. I initially intended to rigidly fix the output to the springs, but experimentation showed that a bungee connecting the output and the car seat was sufficient and smoothed the motion. The problem now was how do I keep the motor speed in sync with the seat’s natural frequency? I decided to put accelerometers on the seat and motor output slider as inputs to a phase locked loop controller running on an Arduino. Although the motor’s speed noticeably varied throughout each bounce, it stayed in sync. All that was needed was a manual startup bounce. Check out the bouncer video.
The bouncer served us well, but the high pitch wine from the motor and worries of the sound being detrimental to our baby prompted me to revisit the design. This time, I opted for a much smaller and quieter motor. It was a Faulhaber gearhead motor, which I got from alllelectronics.com for the hefty price of $9. I machined a nice big wheel that fit the motor shaft with an arm equipped with bearings from which to hang the rubber band bungee. This motor had an encoder built in which proved very handy for reading its speed. I decided to attempt a PID controller to go along with the motor upgrade. My personal projects are in constant danger of being shelved when a more interesting project is conceived and such was the case with the baby bouncer. It was demoted to low priority as I started to build my motorized skateboard.