CanHaptics Lab 1: No-tech puppeteering
(Special shoutout to Hannah for being a fun and helpful (virtual) labmate!)
The task for this lab was to make 3 hardware sketches that move 1, 10, and 100 mm using indirect human actuation. The goal was to try and use do-it-yourself (DIY) techniques to produce rough physical interpretations of our ideas. The sketching and prototyping are “minutes and hours” level.
When you are in proximity of random materials and you play around with them, you automatically get some concrete DIY ideas. My first task was to collect all the raw materials. As I was not at home and in quarantine, I collected all the random objects and materials that I could find in my luggage. I gathered several take-out containers, empty bottles, plastic wrap, wooden cutleries, strings from clothing, lots of granola bars, some art supplies, cardboard cutouts and foam from packaging, metal straws, hair ties, fruits, books, some random objects that I carry around in my compass box, areca nuts, and my beach pebble collection. I realized, I had a lot of resources.
Hannah Elbaggari and I decided to jump on a Zoom call and discussed several ideas together. That was pretty exciting and fun. As a start, my process was picking up random objects from my pile and creating a mechanism, e.g. using a metal tongue cleaner as a catapult and launching pebbles, using wooden cutlery and swiveling it around a joint, or dropping round pebbles off the inclined cardboard. These ideas evolved through several iterations and led to the following sketches.
Crackers and Tea (1mm)
Water bottle, string, plastic box, plastic spool, pebbles, wooden spoon, glue stick, textbook, metal rounder (to make holes), a filled box of crackers, tea strainer, clothing tag, teacup
For this sketch, my initial idea was to translate a larger force to a tiny displacement of 1mm. I set up a string that was tied to a filled water bottle on one end and tucked beneath a heavy book on the other end. The idea was to drop an object from the top and make it slide through the string and create an impact on landing. The plastic spool seemed like a good object to slide as it barely offered any friction.
On the bottom side of the mechanism, I wanted to use the impact force to roll something. When you are rolling an object, the transferred force is reduced and the more distance it moves, the lesser impact it creates while hitting another object. I used a glue stick as the rolling object. Initially, the rolling mechanism (when the spool impacted the glue stick) was not very controlled, so I added a transfer layer of a wooden spoon placed on top of a book. The spool hits the spoon, and then the spoon slides the glue stick. At this stage, I added a heavy object towards the end that would barely move (~1mm) when the glue stick impacts it. The cracker box came in handy. I adjusted the weight removing some crackers.
As a twist, I took a plastic box, added some pebbles inside it, hung my tea strainer, and put it on the top of the spool. So, when the spool is released the tea strainer comes down with it and goes right into my teacup, ready with the hot water! A random clothing tag was used to create air resistance and do some speed control when the spool and plastic box slide down the string.
I really liked how a large force created via stored potential energy was scaled down to make a tiny movement of 1mm. I could have used the same impact force to move objects to a range of distances. Exploring the movement control strategies was fun. For e.g., the rolling distance of glue stick, restricting motion of glue stick using a wooden, using clothing tags and pebbles to control the speed on the string and hence the impact. I feel like while designing any mechanism there should be wiggle room. We should try to design in such a way that it can be changed or easily adapted when the use case changes.
Lever and Pulley (10mm)
Take-out box, pebbles, metal straw, a random 3D printed object, wooden fork, pins, string, cup with water, metal rounder (to make holes), plastic wrap (replacement for adhesive tape)
This idea was inspired by the 1st class lever mechanism. In any lever mechanism, you apply a force to one end of the link and move an object at the other end. The link is pivoted at a point called a fulcrum, the distance between endpoints and fulcrum decides the force transfer ratio. Initially, I decided to lift a small object using a wooden fork pivoted at the rim of a plastic cup. The pivot is unstable as the fork was not constrained; I added clips on each side to allow for a constrained motion.
When I was lifting an object, it was following a slight curve trajectory and it was hard for me to measure it using a scale. So, I created a sliding rail mechanism using a metal straw polled on top of a take out container. The take out container was filled with pebbles for stability. I luckily found a small 3D printed bit in my compass box that quite fits on the metal straw and slides smoothly (fun fact: it is the first object I got 3D printed, back in 2015, when it was expensive and slow; hence the size).
On the side of the fork, where you apply force, I attached a string and passed it through a hole in the plastic cup, creating a pulley. Now, instead of applying vertical force, I can apply horizontal force. To make this mechanism more stable and restrain the cup from toppling over, I filled the cup with water. I also attached a weight to the other side so that the end bit can go back to the normal position when the applied force was released. And here we go!
Stability is an important part of any mechanism! While trying the lever and pulley mechanism in initial designs, things didn’t quite work. Adding stability and constraining motion at each point helped to make the movement controlled and reproducible. Additionally, in this mechanism, there are two levels of force transfer. In lever mechanism, you are translating the amount of force based on the fulcrum position whereas in pulley mechanism you are changing the direction of force itself.
A heavy textbook, cardboard, wooden knives, plastic cup, glue, areca nut (round object), foam
This was the fundamental idea of converting potential energy into kinetic energy and generating impact force causing movement. In the first sketch, a rounded object (areca nut) was dropped from a cardboard plank, attached on top of a triangular podium. It was supposed to move the plastic cup 100mm from its default position, i.e., aside podium. The initial sketch didn’t work as the rounded object’s motion was not constrained. It usually rolled down and followed different trajectories, not quite hitting the cup. Sometimes, the whole cardboard setup got displaced. Iterating on that, I attached wooden knife guard rails to the plank and also restrained the motion of cardboard assembly by placing it against a textbook. Still, there were times when the plastic cup was going beyond 100 mm. I used a stiff heavy box to restrain the cup’s motion but because of the reverse force, it started bouncing back. It was time to use the energy-absorbing foam and it worked!
If you are designing any moving parts in your mechanism, the motion needs to be constrained. If you will not constrain the motion, the moving part might move to uncertain positions or get detached. In this sketch, the constraints were applied for stability on the inclined plank setup, for movement precision of the rounded object, and for position precision of the moving cup. Another thing to mention is that the movement of the plastic cup, arising out of impact, is controlled by changing the rounded object’s launch position on the inclined plank.