ME218A: Soccer Pinball actuators

Posted on Feb 5, 2014

Because of the power restrictions, our design options for the flippers were limited. Normally, pinball machines use linear solenoids, which at 12 V and 3 A are pathetic. On the other hand, DC, servo or stepper motors would be challenging to use. In order to achieve adequate speed, power and mechanical robustness, we opted to use linear door-lock m

ME218A: Soccer Pinball actuators
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otors to push and pull off-axis from the flipper pivot. The flipper design is just fast and strong enough for a well-timed swing, so rather than testing our luck using return springs, we chose to operate each flipper motor in a push-pull configuration, utilizing a bidirectional H-bridge. We operate the motor at full voltage for a predetermined time in each direction, which was based on the minimum complete travel time. In order to prevent blocking code, we utilize timers in the TMRS12 module. Each flipper is constructed from a piece of ½"foam core sandwiched between two identical laser-cut " acrylic pieces, and bound together with glorious hot glue. The main pivot is constructed from a bolt with a smooth shaft section, locked to the playing surface between nuts and metal washers. Nylon washers prevent the acrylic from binding to the components on the bolt. With more time and better resources, we would have preferred to use a true shoulder screw to better control the tolerance stack, however for our purposes this design was more than adequate. In order to make the playing surface removable for easier construction, debugging, etc. , and to control the tolerances of the flipper-motor assembly, we mounted the motors directly to the underside of the playing surface and cut the features for the motors in the same pass/process as for the flippers. The layout of the playing surface and the flipper mounting holes can be seen here....

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