Dual Head Electric Toothbrush

Did you know you are supposed to brush your teeth for 2 minutes strait after each meal ?! That’s 6 minutes per day or almost 116 entire days per life (using the USA men’s life expectancy as of 2021 (last available data)). This invention here does not aim at solving this long standing problem but to divide it by two, better than nothing I guess.

This project aims at rethinking the design of the electric toothbrush

Just like Orthrus, the aim of the 2 heads is to get more work done, follow along this instructable to make your very own !

You can find all stls here

3D printer

Soldering iron (with solder)

~2.5->5V DC motor

18650 battery

18650 battery charger (I salvaged mine from a old 1S powerbank)

3 pins pogo connector (male and female)

Usb-C breakout board

Bistable switch (meaning that the toothbrush can be kept ON and OFF without having to hold the button the entire time)

Electric toothbrush heads

M3 screws

2x Ball bearing (8mm OD, 3mm ID)

Wires (AWG 24 or 26 are fine)

Lets start with the base of the electric toothbrush. The base does not actually contain the charger PCB (for reasons explained in the next point) and is only composed of the male POGO connector and the USB-C breakout board

Now lets move on to the actual electric toothbrush, the circuit is quite simple, it just a switch turning ON and OFF the motor (left of the battery in the circuit) and the charger on the other side of the circuit. The reason why the charger PCB is in the toothbrush and not in the base is that the charger prevents shorts that could happen if the 18650 battery was directly wired to the POGO connector and piece of metal where to short the POGO connector pins hence directly the battery

In order to control the brushes, we need to transform the movement of rotation of the motor to an oscillating rotational movement, the mechanism is described on the picture and on the GIF. Indeed, I measured that the brushes I am using need +-20° of rotation but not more. The 2 output axis (green and orange) are mounted using one screw and a ball bearing and the flexible shafts are glued in the orange and green output axis

The shafts need to be flexible because the second mechanism will bend them to adjust the spread of the 2 brush heads and the flexible shaft allow for continuous rotation event while bending (the bend is kept small as the heads do not need to be very spread). The shaft are made of PLA 3D printer 1.75mm filament which are round but, to engage with the toothbrushes, then need to be squared off. To do so requires to heat the filament (I am using a lighter) and press the softened filament in a square “mold”

This mechanism serves to spread the heads and adjust them to your liking, it is composed of a lever that you move up and down in order to rotate slightly the spread of the heads. The movement is very small (the lever moves ups and down by less than 5mm full range) but since the toothbrushes are quite long (and my jaw not that wide), you get all the tuning range you want out of that little mechanism. The plates onto which the heads are inserted have both the task of guiding the flexible shaft all the way up to the brush but also to allow the movement side to side of each brush. There pivot is held in place by a crimping connector ~2mm in diameter that is glued

This was a fun project but this version is a bit bulky, you can easily find a smaller motor and battery reducing weight and size greatly