Description
In this lab, we were tasked with creating a walker out of a servo motor. After successful completion of the first steps - connecting the servo to an Arduino and controlling it via serial input and a potentiometer - I experimented with various mechanical means of propelling a servo in a manner similar to a walk or a crawl. I thought the best means to achieve this would be to create a one-way joint similar to the human knee. It would contain two rigid rods with a flexible joint in the middle that would collapse when rotated in one direction (allowing the 'leg' to come around) and remain rigid when rotated in the other (to propel the device forward).
Initial attempts were unsuccessful. The rods were either not rigid enough or the joint would slip, preventing proper action. I eventually found a clothespin and realized that the shape of the wooden prongs might lend themselves well to the idea. The grip end of the clothespin is wedge-shaped which would allow the clothes pin to remain rigid when the wedges were against each other, but collapse in the other direction. I then decided to use two zipties as the joint itself; they are rigid enough plastic to keep the wedges of the clothespins against each other but flexible enough that the mechanism would collapse in the desired orientation.
I removed the spring from the clothespin and hammered thumbtacks to the prongs to trap the zipties. After affixing this to the servo plate with paperclips (by threading the unraveled clips around the mechanism and through the holes in the servo plate) I realized my mechanism was too large and would cause the servo to flip. I had to saw one of the prongs to achieve a proper size, and found that the zipties were too rigid for the joint to collapse when the servo actuated in reverse. In essence, the rigidity of the ziptie was great enough to overcome the mass of the servo.
As a result, I removed one of the two zipties and loosened the mechanism slightly. This now worked! The assembly now moves when the servo actuates back and forth. However, the assembly moves in a direction that I did not intend. The clothespin mechanism may still be too tight and seems to propel the assembly "sideways". Surprisingly, this direction is very consistent and repeateable. I believe I may be able to achieve the direction I originally intended by removing the ziptie and affixing another material that is not quite as rigid, but I worry that may cause the assembly to move in a less predictable manner. I've decided, therefore, to keep it as-is. It crawls! Albeit in a manner slightly less efficient than I intended.
I also created a program in arduino that moves the mechanism through an optimal range of motion, and input from a potentiometer adjusts the speed through which the movement occurs.
Materials
1- Arduino Uno
1- Futaba S3003 servo motor
1- potentiometer
1- motor box to serve as the body of the assembly
1- clothespin, spring removed
3- zipties
2- medium paper clips
4- thumbtacks
Code
The code that actuates the servo through the optimal range for this construction and allows adjustment of speed via potentiometer is found at the following link: download here.
Video
I've also attached an animated GIF of the movement of the assembly: click here to download it.
Photos
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