Monday, December 1, 2014

Homemade device to record your iPad with your iPhone using popsicle sticks and rubber bands

This article is cross-posted on the Iridescent blog.



So at Iridescent, we like to live what we preach. We don't just ask kids to make things from scratch, we do it too. Recently I decided that I needed a device to record myself playing games on my iPad (for a separate project to be talked about later). I had done this once before using my iPhone stacked up on a bunch of books and it worked reasonably well. So I decided I wanted the device to hold my iPhone in a position where it could record my iPad. But I also wanted to record myself consistently over the course of a year, so that each time I set it up, it recorded the same way, which meant I needed something better than the stacks-of-books method. It also had to be minimally intrusive in preventing me from using the iPad.

As I thought about this, I realized I had a well-defined design challenge that I needed to solve. Which meant to make things more fun, I decided to use the rule in we use in all of our design challenges: use only low-cost materials.

Additionally, I was always impressed with a Leonardo Da Vinci segment that Bobby Zacharias used in our Be an Inventor program in spring 2012. In the first weeks of that program, students had to design some kind of invention using only the tools and technology available to Leonardo. This meant no glue or machine screws could be used to make connections--things had to be lashed together or connected by pin joints. I always thought that sounded fun, so I decided to put the same constraint on my device.

So, where did that leave me? With a handful of popsicle sticks, rubber bands, and a bunch of ideas in my head.

The final result! Now, how did I get here...


The basic connections

The basis of all my connections involved interlacing popsicle sticks and then lashing them together with rubber bands. This would basically hold the sticks together by tension and friction, as the rubber band lashings pressed the sticks against each other.




I used a similar process for the corners, using two crossed rubber bands to hold the sticks at the desired angles.


The iPhone holder

I roughly measured the size of the iPhone holder and lashed a rough rectangle about that size. The nice thing about using a this method instead of glue is that it was easy to tweak and adjust the positioning of the sticks until it was just right.



I then found ways to make a slightly raised edge on all of the sides to hold the iPhone in place. I added some support sticks on the bottom, making sure not to obscure the iPhone's camera.


The base 

The base was by far the most difficult section to design--the final design shown below was my third effort. I needed something that provided a lot of support for the vertical arm so that it would not bend or tilt forward when it had weight, but was also relatively flat on the bottom, so that it could rest cleanly on a surface. I always intended to put weight on the structure to hold it down, and so this also needed to provide a surface to hold that weight.

An earlier design of the base. It was easier to weigh down this base,
but it was much less stable than my final design.

The final design that worked had a cross-brace and several connections that held the vertical support firmly to the base, but was also connected by a flattened square piece that rested against the table.



I made sure that the base had some thickness to it, so that the cross-brace and other supporting pieces would not be resting directly against the table.


Stability concerns

I was quite worried about stability, as interacting with the iPad could cause vibrations in the table, which would shake the device and lead to a poor-quality video. To compensate, I added several cross-braces to the structure.

A few cross-braces to the vertical arm quite effectively eliminated the up-and-down vibrations.



I added in these cross-braces to the iPhone holder, which eliminated the side-to-side vibrations of the holder itself.



Unfortunately, it does still wobble a bit from side to side. This appears to be caused by the main vertical arm twisting from side to side. It's not a major problem, and in fact my testing of the device found that it worked fine despite this twisting, so I let it be. You can tell from my banging of the table, that any sort of tapping on the iPad itself did not cause noticeable shaking.

video

It was quite interesting dealing with these stability issues; I found myself learning directly why cross-braces were so important to design and how forces were carried through the structure. Of course I'd read textbooks about these issues in different physics and engineering classes that I've taken, but I don't think I really developed an intuition for these forces until I gained this tactile experience by building something.

Conclusion

That's it! The whole building process probably took about 3-4 hours, spread out over a week. There was a lot of thinking in between building sessions, about how to keep the base rugged yet flat, or where the instability was originating in the design. But now I have it, a device to record my Apple device with my Apple device.


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