Automatic baby rocking device?

Electronics
1

hello,
In preparation for my first born I have purchased this bedside crib:
https://uk.joiebaby.com/product/roomie-glide/
As you can see from the link it has a glide function so you can manually rock the child side to side.
I’d like to try and automate this process. Something similar to this:

I think simplicity is the way forward with this project but I have a few questions. So an DC electric motor on a cam pulling a string attached to the bottom of the crib seems like the easiest option. Not even sure if I require a speed control 45-60 rpm should be fine, I think!
I’d really like this to be super quiet in operation, which leads me to my first question. What type of motor will run quiet and provide enough torque for this project? It’s proving to be very difficult to find dB specs for small DC motors. Should I be considering stepper, servo motors as well? I’m also not certain what torque I require, any suggestions?
A windscreen washer motor seems like a good option but I’m worried it will be too noisy.
Is a linear actuator worth considering?
all help greatly appreciated.

2

My first thought was:
Dual pulleys mounted to a gear motor
String wound on each pulley each in opposite directions and connected to the left and right side of the basket.
Motor control for forward and back motion
(I have seen this technique used to control RC boat sails)

Second was a bellcrank-like pulley and lever:
One pulley connected to a gearmotor
Lever connected to the face of the pulley on one end and to one side of the basket on the other.
Motor rotates continuously, the lever is free to rotate as the pulley turns so it moves the basket left and right.

You might get away with a motor (non-gear) and pulley with a string connected to one side of the basket.
Energize the motor to wind up the cord and swing the basket toward the motor under tension. Release the motor and the tension in the basket pulls the cord, basket and pulley in the reverse direction.
Entergize again for the next cycle.

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3

Windshield wiper motors are a good fit. They are cheap and run on 12 volts DC. You may be able to repurpose the mechanism too.

4
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5

Hi, thanks very much for the replies. Does anyone have experience with motor noise levels? The windscreen wiper motor is a great choice as it has a gearing mechanism attached but I worry it will be awfully loud. Is a brushed or brushless motor also a big consideration?

6

I have never measured motor noise so I did and put some measurements below.

I don’t think you will need that much torque to swing the basket so a pulley on a toy motor with cables connected to the basket will probably work. No need for a crank.

You could find out the approximated pull force by using a spring balance. That is if you can find one whose scale is low enough.
https://amzn.to/3DDDZ0Y

I have used these motors and they are easy to mount and cheap.
https://amzn.to/3ImcdcR

You could use this motor, remove the tire and tie the cable(s) to the rim.
https://amzn.to/3y6qc1M

Sound: 10-15db above ambient. Note: to me this was min acceptable for a sleeping baby. Tested at 3V. Motor rpm probably to fast.

These are better gear motors and they come in various speeds:

https://amzn.to/3lHDk8w

Sound: This one did not register on the sound meter tested at 12V, it was very quiet. I tested a 10rpm version.

My guess is:

  • Non-geared motors will run to fast and lowering the speed will reduce the torgue.
  • Geared motors will be a bit more noisy but can run at low speed ranges with plenty of torque.
  • For geared motors noise is inverse to motor quality and $.
  • Brushless are probably less noisy than not, but I think this may be overkill.
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7

Just remembered:
AC synchronous motors could be a good option running continuously they are quiet and run at low speeds with high torque.

here is a rotisserie motor example:

just be careful routing the AC and probably best to use a SSR to switch it on/off

8

Go to your local Thrift store and look for oscillating fans and in the base you will find a nice geared AC synchronous motor designed to be quite and run for hours at a nice slow pace.

9

thanks for all those wonderful suggestions! I’ll let you know how it goes.

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