The Ballkirk Wheel is a GBC based on the Falkirk Wheel ship lift near Falkirk, Scotland. If you want to see it in action, go straight to the video:
I love the concept of GBC and I wanted to build an original GBC module. Ten years ago I got the idea of using the Falkirk wheel. Its continuous mechanism should be just as good at lifting balls as it is at is at lifting ships. Unfortunately back then the inner hole of a large turntable was not large enough to accommodate a 14mm ball plus lane. The only alternative was to use Hailfire Droid wheels but since I was not quite ready to sell a kidney to support my hobby, I dropped the idea.
Fast forward ten years and I revisited the idea. @jojoguy10 built a LEGO version of the Falkirk wheel, but noone had made a GBC module out of it yet. The new large studless turntables have no gears in the centre hole, which means that it's (just) large enough to fit through a lane with balls. So I ordered six of them from Bricklink and started building.
When prototyping I tend to use a mix of colors. This limits search time and makes it easier to discern individual bricks. Once a module is finalised, I recreate it in Stud.io so I know how to rebuild it when my BrickLink orders arrive. This is the first time I used a CAD program during the building process. I had no experience with MLCad or LDD and I started out with the newest kid on the block, Stud.io. There are still a few kinks to iron out but I think Stud.io has a great balance of simplicity and power.
The orienting mechanism makes sure that both gondolas stay upright during the entire rotation. This prevents balls and boats from being spilled. The principle is demonstrated by this video:
LEGO was actually used by the designers to demonstrate the mechanism for the Fallkirk Wheel. My implementation is very straightforward. The center turntable gear stays stationary. As the wheel revolves, the smaller gears between the center turntable and the outer turntables cancel out the rotation of the gondola, thus keeping it upright:
The most challenging part of the build was the intermittent rotation mechanism. The wheel needs to pause shortly to load and unload the balls. Initially, I wanted to use a mechanical solution for this. I have experimented with many different solutions, none of them satisfactory. I started out using a rotating cam that would temporarily block the rotation of the wheel. This did work but it was very imprecise and jerky:
In movie projectors and watches something called a Geneva Drive is used, but I did not succeed in creating a version with sufficient angular precision to reliable loading of the balls. Another possibility involves a sliding mechanism on a piston driver, thus first converting rotating motion into intermittent linear motion and then back to intermittent rotating motion. Although motion was smoother than with the cam mechanism or the Geneva drive, it was even less precise and more bulky.
Eventually I caved and just used a Mindstorms NXT to drive the wheel. The program is exceedingly simple:
Rotate 900 degrees at 80% power
Wait for 1500ms
I'd be really interested if someone comes up with a mechanical mechanism, because using software to solve this issue feels like cheating to me.
Since the mechanism completes one cycle every three seconds, on average three balls should be lifted during each cycle to comply with the capacity of 1 ball per second which is required by the standard. For this, a pusher is located at the bottom of the hopper like in Akiyuki's Ball Cleaner. For the mechanism, I took my inspiration from @Lasse D's ball pump. A counterweight on the back of the hopper smooths pusher movement.
I currently feel the pusher is the weak point in the contraption. Because it is driven by the same motor as the wheel, it spends half the time not loading any balls, thus limiting capacity. Since 5 balls fit on the piston simultaneously, theoretical maximum capacity is 1.66 balls per second. But when multiple balls are stacked in the hopper, the pusher loads less balls per cycle, limiting capacity. One solution would be to use a second motor to continuously drive the pusher but I prefer the contraption to be driven by a single motor.
Controlling Ball Flow
The balls move through the wheel because the entire assembly is tilted. The incline is 1 brick per 15 studs, or 1 plate per 5 studs. This corresponds to an angle of 8% or about 5°. The balls should only move when the wheel runs are oriented with the input and output runs. For this both the input run and the gondola runs are equipped with gates that are closed when the wheel is in transit:
As usual, the simplest solution turned out to be the most reliable. A sliding gate is held town by gravity. The input gate is opened by two 42610c02 wheels [LINK] mounted at the end of the arms, which sadly are not available in Stud.IO. The output gates are opened by the gears of the orienting mechanism, as illustrated in the following image:
The biggest challenge of a GBC is making it reliable. Those little balls have a mind of their own and tend to find every nook and cranny of your contraption to escape it, jam it or even break it altogether. I tested the contraption with beads with large holes which get stuck easier than the standard balls. The Ballkirk Wheel has gone through several revisions to improve reliability:
Incread the incline to prevent balls from stopping in the middle of a run
Like 7 versions of the input and output gates
Enlarged the hopper and the pusher for greater capacity
Several modifications to the pusher to reduce friction and increase reliability
Addition of a counterweight to the pusher for smoother operation
Added a shield to prevent ball spillage at the exit lane
Added a bumper at the foot of the back support to push back balls that have missed the exit
Together, these improvements have resulted in a fairly reliable GBC. I have tested the Ballkirk Wheel for an hour of continuous operation with no blockages and only one ball spilled. Maximum throughput is about 1.4 balls per second.
Thanks for reading this far, I hope you enjoyed it! Please let me know what you think! I haven't gotten around to creating instructions and I'm not sure I ever will. However, if you'd like to recreate this contraption, you can download the stud.io file:
Ballkirk Wheel.io - Stud.io file.