Project Bouncy Ball

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This project idea was initially pitched to SplatSpace by Tom Billman, as a potential project for the March 2011 Hackerspace Challenge.

Accelerometer eggdrop bouncy ball: ball reads force as intensity, color, blinkrate, then plays it back.


Theory of Operation

ball reads force as intensity, color, blinkrate, then plays it back

TODO: Need to explain the educational tie-in

  • how would a teacher use this?

Kristin: When this was pitched at TAR, it was in response to my statement that my kids last year weren't buying Newton's laws because "how did [they] know [they] just didn't hit the puck harder the second time?" It seemed like a way to make "force" visible to students in a way that they would buy in.

  • what does it teach?

potential exercises / games

A Simon-like game where one kid bounces the ball a certain way which creates a pattern of lights and another kid tries to replicate that sequence.

An egg-toss game where the goal is to minimize the Gs that the ball experiences.

Enclosure (a.k.a. The Ball)

Mike and Jeff brainstormed for about 15-20 minutes at the 4/5/11 open meeting about ways to fabricate the bouncy ball enclosure conclusion for first attempt is that Jeff will cast a solid ball (from urethane or silicone) in two hemispheres with a void in the center for the electronics and possibly voids/tunnels for LEDs - if the ball is clear or translucent, the LEDs might not need to be near the surface ball will be created with registration tabs for lining it up there will be a groove around the outside at a right angle to the equatorial cut/separation that will take an O-ring to hold it together

BALL UPDATE: I procured a Kong "biscuit ball" and routed out the equatorial groove to hold the O-ring. (Currently using a rubber band.) Also split it in half with a Dremel razor saw and Xacto- slow hard work. I have 4 LEDs attached to wires and I will pot them into the 4 dogbone-shaped holes with translucent silicone caulk. I can un-do this when we have a decision on where/how many tricolor LEDs to use. I hope to have a simple board encased in it by Tuesday to show the concept. Note- the interior space is approx 3" in dia.

CHALLENGES: The ball has a very thick (1/2"), hard rubber wall, but cutting it destabilized it so that too much energy is absorbed and it does not bounce as well as it used to. It will need filling with firm elastic urethane (I am consulting a mech. engineer about this) to improve the bounciness. Doing this is still vastly preferable to casting an entire sphere which I think would not be easily replicable by all teachers.

I have been unable to find large, solid rubber balls beyond 3" exterior dia. Splitting one of those would be difficult (bandsaw) but it might bounce better. If we could find one.

the electronics

Arduino controlled accelerometer - Peter has ordered some Freescale MMA7455L 3-axis accelerometers battery powered LEDs to indicate force/acceleration and/or playback of same on/off switch?

Bill of Materials

Arduino <== buy from Element14

 - small (Nano?)


 - Freescale MMA7455L

battery/battery holder <== buy from Element14

 - what type? needs to provide 5V, I think


 - count and type TBD
 - do we need light pipes?


 - some sort of on/off switch?

wire pull-up resistors

 - for the accelerometer (or SPI i/f of the Arduino)
 - TBD


 - do we need one?

A possibility for fast prototyping might be to the blinkMs as described here. It's an RGB LED with a built in ATiny85. --skippy


overall: need to track expenditures for the GGHC (to be tracked against the $900 we got for the project) creating a ball that bounces well and can be opened to change batteries

 (and for programming and debugging during development)

making electronics small enough to fit inside ball

 (alternately, casting a ball large enough)

balancing electornics payload such that ball does not wobble needs to be able to survive use and abuse by kids

User Interface

what sort of user interface (UI) does this need to have? - on/off switch - anything else? how will the controls be accessed? what should the LEDs do or look like? what makes sense in terms of "describing" or playing back the acceleration?


Freescale MMA7455L has SPI interface Arduino has SPI support and libraries

 SPI Library
 SPI Library

Software will need to do the following: Initialization - initialize the LED pins - initialize the SPI interface - initialize the MMA7455L Operation - read and store data from the MMA7455L - play back data via the LEDs

alternate power idea

a possible way around having to open the ball to change the batteries would be to have a rechargeable battery fully sealed inside the ball and have it change a battery via an inductive circuit; something along these lines ... general info:

 Inductive charging - Wikipedia, the free encyclopedia


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 DIY Charger - DIY custom cellphone induction charger
 Update: Custom cellphone induction charging - Hack a Day


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