Hi-Strikers

Winter 2017, Winter 2018

The classic carnival game, digitized! This was my first project for wonderMakr, as a freelancer helping them out over the holidays. It was so much fun to stretch my creative technical problem-solving muscles! I got the chance to do the project a second time a year later, and try some different ideas.

The Approach

After doing some research into how other people had tackled this project, I settled on the concept of using a digital air pressure sensor inside a sealed rubber hose that sits under the striker post. When someone drops the hammer onto the post, it'll momentarily compress the hose and increase the air pressure inside. I decided to use automotive grade components to be as robust as possible.

The hose is expected to be a consumable - there's no great way to ensure it won't wear out and get leaky over time. That's why I made sure the sensor was a separate package that could be disconnected.

Shopping List

Arduino Uno [DigiKey], [Amazon]
DMX Shield: Tinkerkit Shield (now obsolete) [DigiKey], DFRobot shield [DigiKey]
3-pin XLR connectors [DigiKey] and cable [Amazon] to connect the controller to the sensor in the striker post
MPX4250AP Air Pressure Sensor [DigiKey]
Heater Hose [NAPA Auto Parts] - this took FOREVER to find the perfect hose, you're welcome.
Potentiometer [DigiKey], Knob [DigiKey]
Enclosures [DigiKey], [DigiKey]
Power Supply [DigiKey]

Integration

This was a custom fabrication, which used DMX lights up the main column. The fabricator also made their own giant mallet!

This is meant to be set up and used outside during the day, which is why the lights are so blindingly bright.

This system worked really well; I didn't hear of any issues while it was in use for at least a year. I did provide replacement hoses, and a replacement sensor, just in case. Overall it was a super fun project!

Round 2

I got the opportunity to build another hi-striker a year later. While extremely time-constrained (literally 2 days given to order and build), I wanted to try a different approach. Knowing that the first approach worked well (so I had a backup plan), I tried an accelerometer this time. My logic was that this would hopefully remove a consumable from the project, as the hoses were very expensive - I hadn't discovered the heater hose at NAPA yet, so was buying small radiator hoses from Canadian Tire that were custom-formed for specific vehicles... not cheap at all!

I installed the accelerometer into a 1/2" piece of wood that would sit between the 4x4" wooden striker post, and rubber stoppers at the bottom. I made sure to use an accelerometer with 16g of range, assuming the instantaneous strike would be a lot of force.

Long story short, this was not a good approach. The accelerometer provided very inconsistent values, depending on if you hit the post dead-on, or slightly off-centre. Worth a try! So I reverted to the hose and air pressure reading approach. I'm still sure there's a better sensor solution out there (like a proper force sensor), but I didn't have the time or money to investigate that further.

Another note: this time there was no special custom-fabricated mallet. I went with this 8lb dead blow sledge from Princess Auto. It seemed perfect, but this striker got some very heavy use, and I learned these hammers weren't really up to the challenge.

I couldn't find anything better, though. The learning is either get something custom-made for this with a larger head, or ensure the striker post has a wide striking surface. That way you can guarantee more direct hits, which deliver the least damage to the parts.