Rotation to Linear Motion

Ways of turning the spin of micro servos into straight lines

By Sauda Musharrat

This tutorial is meant to demonstrate one of the ways in which we can transform the rotational motion of motors into linear motion. Motors such as Servo and DC are often used for many kinds of projects. However, rather than only being constrained to a circular movement for objects attached to the motor shafts, we can translate the continuous rotation to repetitive linear motion with a few extensions and tools. We used cardboard in this tutorial to get you started on this method but it can easily be replicated with other materials for a more sustainable and long-lasting model.

The basic principle of this system came from this tutorial:

https://www.youtube.com/watch?v=WynJqz-hibA

Materials

 

  1. Cardboard and some colored paper
  2. Micro servo motor 
  3. Thumb Tacks, 1/2″ Head, 5/16″ Length
  4. Glue gun or super glue gel
  5. Box cutter or large scissors
  6. Painters tape
  7. Arduino (any model would do)
 
Step 1: Determining the bounds of the linear movement

gctrsets

Step 2: Cut out the three arms

 

Its a good idea to wrap a smooth layer of packing tape on the arms to reduce friction. It is also recommended to laser cut the arms to maintain consistent width (unlike the irregular shapes documented in this tutorial). This will ensure the third arm remains within the path/channel where motion is restricted.

Step 3: Code and align the servo shaft

Arduino code:

https://drive.google.com/file/d/17RX9k0_89rpxjtDywYTmbzMPeWSl3BI7/view?usp=sharing

This servo has been programmed to rotate from 0 to 180 degrees over 3.6 seconds, wait 3 seconds, rotate back to 0 degrees in 2 seconds, wait 3 seconds, and repeat the cycle. Adjust the arm on the shaft to be perpendicular to the width of the servo.

Step 4: Joining the arms
Hot glue the first arm along the servo arm
Use thumbtacks to join two arms. Seal off the end using a dab of hot glue
Start from the center and punch a hole with thumbtacks on the extended end where the second arm will join
The second arm to see if it moves freely along the pivot point
Step 5: Preparing the arm that will move linearly

Join the third arm in the same way as you did with the first and second. Test to see if the second and third arm move freely along the pivot. Use a layer of packing tape over the third arm and attach the objects you want to move linearly at the end. Here I used a small cardboard red circle to follow the path of motion.

Also make sure the path/channel through which the third arm will slide in and out is at the same level with the servo height. Here I used random household objects to elevate the channel and keep servo and arms at the same height.

Step 6: Making the path on which the motion will be constrained

This path/channel can be a tube or any enclosure based on your project. As long as it is not too tight or too loose, secure, does not provide alot of friction (you can coat it with packing tape) and at the same level as the arms, it should hold. Be prepared to do some trial and error!

Alternative Method: Rack and Pinion

The rack and pinion method is also a great way to turn rotation to linear motion. I have found that using wood or strong dense cardboard, the gear teeth will be stronger to hold/support objects of more weight than the  previous method. 

The basic idea is to attach (hot glue) the round gear (pinion) to the servo arm aligned with the center. Then create a mount for the servo and a channel for the rack on the same level/surface based on your application or project. 

I will update this post with an example project that will detail how one such mount and path can be made.

Link to the laser cutting file:

https://drive.google.com/file/d/1F-h8ab8sWMst2fsjczpm1xH4nGyhVQAB/view?usp=sharing