Roby the Robot Dog gets a 3D Printed Servo Tail

Roby is my 7 year old son's mBot and Meccano based robot dog. And he wanted it to have a wagging tail. Actually the tail was prototyped before we settled on the dog design.

The tail was a project that my son worked on with his Dad. They came up with the idea of using a series of discs in decreasing sizes and controlling them by pulling a fishing line cord with a servo.

This idea worked really well and I helped them to add the tail to Roby and code the servo movements.

If you haven't read our introductory article about Roby the mBot robot dog then you might want to start there.

Roby's tail

Roby's tail is made from:

• 3D printed discs
• a cable tie
• fishing line

The discs were 3D printed with holes at the edge for the fishing line to go through and holes in the middle for a cable tie.

My son and his dad also designed 3D printed parts to attach the tail to Roby's rear end which is made from Meccano. The servo board is also attached to the Meccano using nuts and bolts.

There's 3D printed wheel to attach to a servo to pull the fishing line to tighten and release the tail. And there's an all-important paper-clip to stop the fishing line slipping off the wheel!

The tail was prototyped before we built Roby's body so it's a little big (as my son keeps pointing out to his dad!) We'll probably switch it for a smaller one at some point, but for now it proves the concept and allows us to program the tail behaviour. And it has taught my son about prototyping and iterating on a design.

Here's Roby's tail wagging:

Roby is built on the mBot platform from MakeBlock and we have a servo extension kit which was perfect for this project. The servo is controlled by Scratch code with additional blocks for controlling the mBot components.

The tail can be made to wag when a key is pressed and you have accurate control over the servo position so the tail position can be used to indicate the dog's mood or to fit in with other behaviours.

Scratch MakeBlock mBlock code for tail wagging

Note that you have to select the Port that the servo adapter is connected to and the slot - you can run two servos from a single mBot mCore port which is really handy.  Setting the angle of the servo using degrees was easy for my son to understand.

Eventually Roby's tail wagging will be built into her behaviour so she wags her tail when she's excited and when she dances.

This was a great project for helping my son understand how servos differ from the motors for making robots move around that he's more familiar with.

There are lots more features planned for Roby. You can subscribe to the Tech Age Kids mailing list to see future updates on Roby's programs and extensions.

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