Switch Adpated Hungry Hungry Hippos

I thought it could be pretty cool to try switch adapting the Hungry Hungry Hippos game. In researching what had already been done I found this product from Enabling devices which is a mechanical adaptation utilizing a paddle to make pressing the lever easier. I also found this project from the UConn Biomedical Engineering program which used motors and was switch adapted.

Below is a video of my version in action. It’s a little more compact (just a servo, arm and paper clip) but also for now just focusing on the eating lever of each hippo.

Here’s the servo and bracket setup that I used for each hippo. The bracket is from Lynxmotion and the arm parts and servo were from ServoCity:

Below are pictures of the control board. The servos could be simply driven from an Arduino directly, but I decided to solder together a more robust board with a few extra features. The essential components are the microcontroller, switch jacks, servo pin headers, and power jack.

Since the servos I was using exhibited a motor whine even when just holding position I needed a way to idle them. Unlike analog servos, digital servos keep trying to hold their position for as long as they have power even if you stop sending them a control signal. So for this I added a transistor for each servo acting as a low side switch, cutting off power when the servo is not in use. Also, these servos draw a huge amount of current when moving quickly out of a full stop. Though powering them from 4 D batteries worked fine, most of my power supplies would temporarily shut down when detecting the sudden huge current draw. To rectify this I added a very large capacitor that was able to supply the initial surge current needed. Again, using battery power instead, different servos, or moving them more slowly would have also worked.

I opted to hot glue the control board under the center of the game board to better conceal and protect some of the wiring and electrical components. I got some Duplos from my daughter to act as risers for the game board.



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