Convert Rotational Motion Into Linear Motion

In this project, we’re going to show you how to convert the rotational motion of a servo into linear motion which will eventually move “Grumpy Greg” up and down. This will be achieved using a lead screw and nut system that is connected to a scissor linkage mechanism. These engineering principles may sound complex but in reality are very simple and extremely effective when building robots or machines.

This project goes beyond basic making and programming, providing an additional challenge by using several engineering mechanisms. You’ll see these mechanisms and terms mentioned throughout this post, so let’s take a moment to define each of them before proceeding .

Project Glossary

Scissor Linkage Mechanism– A mechanical structure composed of connected, folding supports arranged in a crisscross or X-pattern. It operates by extending or retracting the linkages to achieve vertical movement.

Lead Screw & Nut System – This system converts rotational motion of the servo into linear motion. It consists of a threaded screw mounted on to the servo and a matching threaded nut that moves along the rod when the screw rotates.

Horizontal Linear Motion – This is movement of an object in a straight line parallel to the ground without any vertical movement. In this project, the wood bar only moves horizontally when the screw turns.

Vertical Linear Motion – This is the up and down movement of an object in a straight line. In this project, the scissor linkage only goes up or down.

The photo below helps to show how the lead screw and nut system are interconnected with the scissor linkage mechanism. When the servo turns, it will spin the connected screw which is threaded into a fixed nut. Since the nut is fixed in place, the only thing that can move is the wood bar which moves in a linear motion along the screw as it rotates. This wood bar is connected to our scissor linkage mechanism. When it moves inward, it will make the scissor mechanism extend upward which creates the vertical linear motion. So essentially, we’re turning the rotation of a servo into horizontal and then vertical linear motion which raises the head of the “Grumpy Monkey”.

This is a fun project that also uses a light sensor to call a “doorbell” function which are notes coded on a micro:bit and transmitted via the Hummingbird speaker. Once the notes are finished playing, it will start the lower servo in motion.

Materials Needed

In order to create this project, you will need the following items:

Note: All of the electronic parts of this project can be found in the Hummingbird Premium kit

Cut Cardboard Cross Supports

To begin this project, we will need to create the cross arm supports for the “scissor lift” mechanism. In our design, we made them 1″ x 9″ in dimension but you can make yours larger or smaller. Use a ruler and sharpie to create the outline of these supports and then cut them out using a utility knife.

Pro Tip: Not all cardboard is created equal. We found some scrap cardboard but it was very thin and lightweight. In order to make it stronger, we laminated two pieces of cardboard together using hot glue. This took a piece of 1/8″ thick cardboard and created cardboard 1/4″ in thickness. Some projects require material with extra structure and this is a simple way to do it. Also, instead of using cardboard, you can substitute large popsicle sticks in place of it. This will however require a drill or heavy duty punch in order to make the holes in future steps.

Make (3) “X” Cuts In Each Support Arm

Once the cardboard cross arm supports are cut, you will need to measure where the brass brads and dowel rods will be placed. Measure to find the middle and draw a line the length of the support. Next, draw another line to indicate the center in addition to spots on each end that are 1″ in from the edge. Cut an “X” where the lines intersect. You should have (3) “X” cuts on each support arm.

Place Brad Brads In Support Arms

Push the brass brads through all of the “X” cuts you made in the support arms. Do not bend the brads at this time as this will need to be done in the next step. Note – Some of these brads will be removed later in future steps and are simply used as a placeholder for the time being.

Create a Mechanical Linkage Mechanism

A mechanical linkage mechanism is an assembly of systems that are connected to manage forces or movement. In this case, we will be creating a scissor linkage mechanism by combining two arms together using the brass brads. Place one cardboard arm perpendicular to each other. Remove the middle brass brad from the bottom support arm. Push the brass brad on the top arm through the middle hole in the bottom arm and then bend the back of the brad to lock it in place. Follow these steps again to make the next 3 scissor linkage structures. Grab the bottom legs of the structure and move them inward to make sure that they move freely.

Create a Complete Scissor Linkage Mechanism

At this point, you should have created (4) separate scissor linkage mechanisms. Place one of the “X”s on top of the other and connect them using the brass brads. Make sure they are connected as shown in the photo below to ensure a smooth movement. Push the bottom legs together to make sure they lower and rise correctly.

Create The Base & Sides

Cut a piece of cardboard measuring roughly 11″ x 11″ in size for the base. For the side structures, we used wooden rulers that were laying around our makerspace but you could also just use thick cardboard. The sides needs to be sturdy, so if you’re using cardboard make sure it’s reinforced as described earlier. The side structure measures 2″ high by 11″ wide. Cut a hole the same size diameter of the wooden dowel rods you are using at about 1″ from the end and 1/2″ from the top. Hot glue both of the side structures to the base.

Attach Scissor Linkage Mechanism

Now it’s time to attach both scissor linkage mechanisms to the base and sides. Cut (5) dowel rods to 12″ in length. Push (1) of the dowel rods through the bottom of the cardboard arms all the way to through the bottom of the opposite scissor mechanism. This dowel rod should sit on the top of the side supports. The left side (as shown below) is constructed the same way but this time the dowel rod will also go through the holes that were cut in both support sides. Finally, insert dowel rods through the top 3 holes where the brass brads are currently. When you’re finished, test the mechanism by pushing on the dowel rod that is resting on the side support. If built correctly, the mechanism should extend upwards.

Prep the Push Rod

Now it’s time to build the opening that will house the nut that the screw goes through. Add two pieces of cut dowel rod below the main rod making sure the gap is big enough for the nut. Once both pieces are hot glued in place, attach another full piece below it to complete the structure.

Attach The Nut

For this push board, we used some scrap wooden rulers but you can also use thick cardboard or craft sticks. Cut a small hole in the center of the wood or cardboard so the nut can be glued in place. Make sure the nut is firmly in place and glued so it WON’T spin.

Attach Round Servo Horn To Servo

Attach a round servo horn to one of the rotation servos using the screw that comes with it. Normally you can pressure fit a servo horn without screws but in this project it is very important to use the screws.

Attach Bolt To Servo Horn

Using hot glue, attach the end of the screw to the round servo horn. Make sure to carefully put hot glue on the back side of the servo horn as well as the front side and all around. This will help make sure the screw stays firmly attached while it is spinning. Ensure you don’t accidently get hot glue on the servo shaft which could prevent it from spinning.

Mount The Servo and Bolt

In this step, we’re going to create a little box for the servo to be mounted in. This will help elevate and secure the servo and will allow the screw to fit horizontally into the nut. Begin by carefully threading the screw into the nut. Once in place, you can see how much cardboard is need for the servo to be level. Secure the servo in place with a rubber band or hot glue it for a more permanent installation.

Create Upper Platform

Cut a piece of cardboard roughly 5″ x 11″ and secure it to the left side of the upper dowel rods using zip ties. The other side needs to be free to move when the platform is raised and lowered. To the left or right of the upper center dowel rod, cut a rectangle smaller than the overall servo. This will allow it to fit through the opening but still stay on top of the platform. Make sure to attach a round servo horn to the servo. In this case, the screws don’t need to be used to secure the horn.

Build The Monkey Head Structure

For this project, we found a stuffed monkey from the “Grumpy Monkey” book series by Suzanne and Max Lang. Unfortunately for Jim Panzee (the name of the monkey in the book) we only needed his head. Sorry Jim! Yet another reason for this monkey to be grumpy.

Place the head on a piece of cardboard and trace around it. Cut this piece out and attach it using hot glue to a small cardboard circle. Remove most of the stuffing from the head and slip it over the head structure and glue it in place.

Attach Monkey Head To Servo

Next, you will need to hot glue the monkey head to the top of the round servo horn. Again, be careful not to drip hot glue on the servo shaft which could prevent it from rotating.

Connect To Hummingbird Bit

Now for the fun part which is connecting all the electronics to the Hummingbird Bit. Attach the servo cable from the upper platform to servo port #2 on the Hummingbird. If the cable doesn’t reach, you may need an extension cable. Next, attach the cable from the lower servo to servo port #1 on the board. Make sure the white wires on the servo cables line up with the “S” or Signal on the servo ports.

Plug the light sensor into sensor port #1 and make sure the yellow wire goes to the “S” and the red wire goes to the (+) positive and the black wire to the (-) negative.

Lastly, plug in the battery holder and make sure there are (4) AA batteries installed.

Build The Outside Box

Now that the main structure has been created, it’s time to build the outer box that will house our grumpy monkey. Measure your structure to determine the exact size for your outer box and add 1″ to each side. In our case, our box needed to be 12″ x 12″ x 12″. Hot glue 5 of the 6 sides of the box in place and leave the top open as the top panel will be on a hinge. To create this, we are using wood bamboo skewers but you can also use crafting wood. Take a straw and cut (3) pieces about 2″ long each. Slide the cut straw pieces onto the bamboo and elevate it in between the straw pieces using wood or cardboard. Hot glue the straw pieces to the lid and the visible bamboo sections to the elevated wood pieces. Open the lid and verify it moves freely.

Monkey In The Box w/ Doorbell

The last construction part of this build is to fabricate a doorbell. On the front of this box, cut a small hole and push the light sensor through it. Cut small strips of cardboard and hot glue it together in order to resemble a doorbell. Make sure the front of the doorbell has an opening and the light sensor is visible. When you press your finger over the hole, it should block out all the light which will trigger the light sensor.

Put the monkey in the box with all the connected electronics. At this point you can decorate the front.

Programming The Servos & Sensor

Now it’s time to make this project come alive. For this project, we used Microsoft’s MakeCode which is free to download and use.

  • Insert the micro:bit into the Hummingbird Bit controller
  • Connect the battery holder to the Hummingbird and turn it on
  • Connect the USB cable from your computer to the micro:bit
  • Go to https://makecode.microbit.org
  • Click on “New Project”
  • Give your project a name and click “Create”
  • Download – “Grumpy Greg” ZIP folder which contains (1) HEX file
  • Drag the HEX file into the middle of the MakeCode work area
  • Click the purple “Download” button on the bottom left of the screen
  • The code should be sent to the micro:bit after a few seconds

IMPORTANT – Make sure the battery holder is turned on. The servos won’t work until the batteries are powering the unit. Test to make sure everything works by covering the doorbell hole. You should hear the doorbell ring and then the servos should start operating.

More Projects & Resources

If you end up making this project, we would love to see it. Tag us on X at @BirdBrainTech so we can share it with our community.

Looking for other Hummingbird Bit projects? Check out our Birdhouse Blog or our project pages for more inspiration and ideas.

Project Parts

If you’re looking to purchase the parts used in this project, make sure to check out our store to learn more about the Hummingbird Kit, Finch Robot and the other exciting products from BirdBrain Technologies.