Servo-motor Adapted to Lego




Introduction: 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.

Next Instructable: Servo-motor converted to motor

Step 1: 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

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

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

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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    15 Discussions

    How can you be certain to cut the cross so that it is accurately centered? If it isn't right you get wobble and the gears wont mesh leading to jamming, slipping and stripping. I've fitted lego gears to servo horns which helped me get perfect center but alas they become cumbersome. I would like to make mine as low profile as yours if I can get a good center axis.

    I get the servo motor from AliExpress.

    The parts are sticked with hot glue. See the picture 6 on the step 4, I remove the excess of glue.

    Good question ! It's an actuator commonly used in RC models. To answer you clearly, I added a video in the Instructable. In this example, the servo motor is connected to an Arduino board.

    My daughters are going to love this - thanks for the great instructions!

    This is one of those things that just /needs/ to exist. Genius!

    This is an awesome idea! Thanks for sharing!

    Lego is wasted on kids. This could be useful for some of mine though.

    Great Idea. Geat I'ble too. You could also modify another set of servos to be non-stop or constant run. My son has lost interest in his Legos. I've been wondering how I could get him back into them again and introduce him to Arduino as well. This would more than do both.

    1 reply

    Yes, I modified some of my servo to became non-stop motor. It is great. I've done some photos to prepare my next Instructable on this theme. See you soon !

    Awesome idea. I need to make this for my son's lego collection. Thanks.