The idea of a claw machine game at an arcade is fantastic. You get to operate a robot in an attempt to retrieve prizes! What could be more fun than that? Sadly, most of us have learned that the claw machines out in the wild are completely rigged. That isn’t a conspiracy theory, it is undisputed fact. And it ruins all of the fun, because it makes your persistence and skill irrelevant. But you can have all the fun without any of that frustration by building Geo’s DIY Pico Claw Machine.
The functionality of a claw machine (and all of the “challenge”) comes down to the design of the claw gripper mechanism. Those look pretty straightforward, but they’re actually engineered intentionally to grab things as poorly as possible. The first part of that poor performance is a result of the “finger” shape, which has a smooth, gentle curve that can’t catch on prizes. To lift something, you really have to get all three fingers well under the object.
But the claws have a more insidious design “feature” that makes the situation much worse. An electromagnetic solenoid actuates the claw-closing mechanism and it doesn’t do so with much force. And here’s the kicker: the machine can vary power to the solenoid in order to adjust the grip force. That’s how these machines are rigged: the operator can program the machine to grip with low strength until they’ve made enough money to allow a win. It is also possible to program the machine to grip with low strength in certain positional zones — like where the high value prizes sit.
Geo’s DIY machine uses a standard claw gantry mechanism (available from places like AliExpress), but he set it up to grip with adequate force every time. That mechanism includes most of what you need to replicate this project, you just need a frame to house it, Y axis guide rails, a power supply, and a way to control it.
Geo built his machine from recycled materials he had on hand, but you could do this with aluminum extrusion or whatever is convenient. Power comes from a 12V 2.5A power supply. To control the motors, Geo used a Raspberry Pi Pico W development board. It interfaces with the claw controller through a custom cable, with two L298N-based dual H-bridge drivers for the motors. The user controls are a joystick and arcade button.
At the moment, Geo’s niece mostly uses this machine for playing with LEGO, and frankly, that seems like a lot of fun and we’re jealous. When she gets older, Geo can start rigging the machine to teach her important lessons about the real world.