Laser cut ball lifter.
I've been playing around with ball lifter designs for a while now, and none of them have been particularly satisfactory. They have either required too much time and effort to make and so would be uneconomic to sell them at an affordable price, or have been compromised by using off the shelf parts that don't fit together well enough to prevent the ball lifter from jamming up all the time.
After seeing the design of the Pibow case for the Raspberry Pi, and how it is made from a stack of laser cut acrylic parts, a little lightbulb appeared above my head and I wondered if it would be possible to make a ball lifter out of a stack of laser cut acrylic. That way the laser cutter can do all the hard work, and I'll just have a pile of parts to stack up and screw together along with a motor and a switch.
Out came the CAD package, so I could sketch the concept out and see if it would work. The design is heavily influenced by the orange ball lifters from Japan, so uses a duplex gear. The design of the gear was the most complicated part, you want the balls to nestle nicely between the two halves of the gear with no gaps between adjacent balls, so there was a fair amount of maths involved in calculating the sizes and spacing of the teeth.
drawing.png
The parts were then laid out onto a single sheet and sent to my local plastics fabrication shop to laser cut. A small motor was ordered from an eBay seller and a microswitch was found in my junk box. A few nuts and bolts later and voila...
Ball_Lift.jpg
There are a few issues with the design, the motor isn't really powerful enough, it can just about manage to lift balls the full height of a pachinko machine, but it's really struggling and slows down to about half it's no-load speed. I was expecting this, and have already ordered a more powerful one from a seller based in China, but the one I've got was the best one I could get from a more local seller in a more reasonable delivery timeframe. The other benefit of a weak motor is that you are less likely to break anything if there's a jam.
The main problem is that the acrylic gear isn't really robust enough, there are already signs of damage to the teeth. The heat from the laser cutting process makes the cut edges quite brittle and the hammering it gets when it's pushing a stack of balls the height of a pachinko machine is a bit too much for it. The next prototype I try will have the laser cut parts annealed (gently heating and cooling the parts to remove the heat stress from the laser cutting), if that doesn't work then I'll have to try making the gear from something a bit stronger (nylon or acetal/delrin).
The plastics shop is cutting and forming a ball catcher/tank to sit behind the lifter, and with a bit of luck I should have that to play around with for the weekend, and I can get rid of the duct tape stopping the balls from falling out the back!
A 30 second video of it running should be available on this YouTube link.
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