Servo-motor adapted to Lego

Written by: roboguru

Picture of Servo-motor adapted to Lego

Hi, this is my first Instructable, I hope you will enjoy it !

The aim is to control Lego buildings from Arduino boards with low cost parts. This first projet consists in adapting the traditional servo-motor 9g to plug it with Lego blocks. It takes place in a more global projet that my godson enjoys, and that I will describe you through several Instructables.

The total cost is under 5 euros.

Step 1: Materials and components

Picture of Materials and components


  • cutter
  • hot-melt glue applicator
  • precision screwdriver (adapted to servo-motor screws)
  • some Lego blocks


  • servo-motor 9g
  • Lego gear 16 tooth (light bluish gray)
  • Lego liftarm 1 x 3 Thick (light bluish gray)

The Lego components can be easily purchased from Lego parts suppliers such as ToyPro.

Step 2: Preparing the servo-motor

Picture of Preparing the servo-motorSTEP_2_1.jpgSTEP_2_3.jpgSTEP_2_4.jpgSTEP_2_6.jpgSTEP_2_2.jpg

This step consists in cutting some parts of the servo-motor in order to adapt its size and the profile of its gear train to Lego.

First, plug the servo arm to the servo-motor and manually turn the arm to set the position at the middle point. This step is optional but is useful if you prefer to plug something other than a gear(see an example in the next step). Then cut the gear train in order to have the cross shape of the Technic Lego connectors.

Secondly, cut flush the handling support distant from the gear train. Then, cut the handling support near the gear train while ensuring a length of 3 Lego units from the other side.

Lastly, scrape the tow sides of the roof on which Lego parts will be glued. It is to roughen the surface so that the hotmelt glue will adhere well.

Step 3: Preparing LEGO parts

Picture of Preparing LEGO partsSTEP_3_1.jpgSTEP_3_2.jpgSTEP_3_4.jpgSTEP_3_5.jpgSTEP_3_6.jpgSTEP_3_7.jpgSTEP_3_8.jpg

Firstly, cut the Lego liftarm in order to obtain two similar parts with the thickness of the Lego pins. Simply plug the liftarm in a plate and cut it at the top of the pins.

Secondly, cut the gear in half. Turn the gear while cutting for a uniform planing. You will perform two equivalent pieces, the second one may be used to convert another servo-motor ;-)

Note: this Instructable details a gear mounting, but you can easily replace the gear by a Lego part of you choice. The mean is to adapt the thickness of this part to be compatible with Lego buildings (see the example in the last picture).

Step 4: Fixing the Lego parts to the servo-motor

Picture of Fixing the Lego parts to the servo-motorSTEP_4_1.jpgSTEP_4_2.jpgSTEP_4_3.jpgSTEP_4_4.jpgSTEP_4_5.jpgSTEP_4_6.jpgSTEP_4_7.jpgSTEP_4_8.jpg

Firstly, you must prepare a Lego assembly to glue the attachement parts at the good positions. When it is done, apply the hotmelt glue with the applicator. Take time to warm up the servo motor plastic to ensure a proper adhesion. Place it quickly in the Lego set, and press until the glue has cooled.

Revert the Lego assembly to repeat the operation on the other side. When it's done, you can easily cut the surplus of glue.

And finally, place the gear and add a drop of glue before screwing it.

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