[GBC] Ballkirk Wheel

[DaFokka]

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:

 

Conception

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.

Building Process

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.

Gondola orientation

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:

Retarding Mechanism

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:

1. Rotate 900 degrees at 80% power

2. Wait for 1500ms

3. Repeat

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.

Loading Hopper

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:

Reliability

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.

Summary

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.

[Philo]

Great GBC module, excellent presentation and explanation!
 

Quote

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

Wheel+tire shortcut may not be there, but the rim and tire should be available (42610 + 50951 )

[Blakbird]

I love the title!  There are a couple of possible solutions for intermittent motion.  One would be a Geneva mechanism.  Akiyuki also invented such a mechanism for the wheel of his bucket factory.

[doug72]

Great GBC - well done.
I have long wanted to build a Falkirk Wheel but never got around to it !

Unfortunately can't open the zip file on Mac OS.

[Philo]

You should be able to install stud.io on your Mac... http://studio.bricklink.com/v2/build/studio.page

[doug72]

1 minute ago, Philo said:

You should be able to install stud.io on your Mac... http://studio.bricklink.com/v2/build/studio.page

Thanks for the info and download link. Will be installing it soon.

[dr_spock]

Great GBC idea and well executed.  

 

[DaFokka]

Thanks for the compliments, guys!  I spent quite a lot of time finetuning the module and I had a lot of fun! The real challenge is in making it reliable. Now I am working on a module that can create worst-case bunches of 30 balls at once for more rigorous testing of modules. I'll call it the Tsunami.

3 hours ago, Philo said:

Great GBC module, excellent presentation and explanation!
 

Wheel+tire shortcut may not be there, but the rim and tire should be available (42610 + 50951 )

The tire (50591) is available, but the rim isn't. Might be a bug, there are more parts missing (like the PF L motor for instance).

[ColletArrow]

This idea is brilliant and well executed. I agree a timing mechanism would make it more interesting than running it off a Mindstorms, but I can't think of how to build one. And the title...

[Splat]

Great GBC.  It is always nice to see an original GBC module.  

[Kristof]

Wonderful! Once again a very original new GBC. I totally agree that having purely mechanical drive would be cooler but I see the issues that make it difficult. Alltogether, great work!

[Philo]

Quote

The tire (50591) is available, but the rim isn't. Might be a bug, there are more parts missing (like the PF L motor for instance).

If you type in rim design number (42610) in Stud.io search box you'll find it. Indeed the L motor seems missing, a bit weird since Stud.io uses LDraw library and this motor was modeled a long time ago...

[DaFokka]

20 minutes ago, Philo said:

If you type in rim design number (42610) in Stud.io search box you'll find it. Indeed the L motor seems missing, a bit weird since Stud.io uses LDraw library and this motor was modeled a long time ago...

Even if I search by number, the rim is missing; at least on my PC. Must be a bug or something

[Philo]

Or something indeed... I installed latest stud.io and 42610 is no longer there... though model is still present in C:\Program Files\Stud.io\ldraw\parts folder :(

[dellock6]

They are there most of the times, just hidden from the interface. For example, almost the entire set of Power Functions components is hidden too. I found this tutorial (http://forum.bricklink.com/viewtopic.php?f=3&t=419&sid=ea4c15443b891eb5eba5ddaf4672d338#p963) that explain how to un-hide the different component, a bit cumbersome but it does the job. Not sure however which consequences there may be by unhiding, for example on the collisions engine. It worked for me tough to enable some PF engines and some rims.

Edited March 5, 2017 by dellock6
Forgot the link...

[Philo]

Thanks for the tip, dellok6!

[doug72]

On 04/03/2017 at 5:57 PM, DaFokka said:

 

Retarding Mechanism

 

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:

1.  

   Rotate 900 degrees at 80% power

2. Wait for 1500ms

3. Repeat

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.

Intersted in building this GBC and have been trying to come up with a simple retarding mechanism.
On my Ferris Wheel GBC if the arms jam then the white clutch gear slips and arms stop - once jam is fixed rotation continues without any jerks.

I have come up with a possible solution that might work, using a worm drive to the white clucth gear with a normal 24T gear engaged with the clutch gear.

Red axle = input from drive motor.
Yellow axle = drive for lift rotation.

The 24T gear on the grey axle has a disc which 4 holes around its circumference - two holes have axle /ball pins which would engage with a trip mechanism to block rotation at 180 deg intervals.

With white 24 T gear slipping the 24T gear still rotates activating the trip system, once trip de-activated and releases the lift, white gear drives the yellow axle again for another 180 deg. rotation.

Re Geneva Gear:
I have been hunting on line for a two arm version without luck but came a cross a 3 arm version - still hunting !

Another possibility is a Scotch Yoke / Crank device with built in dwell.

 

Edited March 7, 2017 by Doug72

[DaFokka]

1 hour ago, Doug72 said:

Intersted in building this GBC and have been trying to come up with a simple retarding mechanism.
On my Ferris Wheel GBC if the arms jam then the white clutch gear slips and arms stop - once jam is fixed rotation continues without any jerks.

I have come up with a possible solution that might work, using a worm drive to the white clucth gear with a normal 24T gear engaged with the clutch gear.

Red axle = input from drive motor.
Yellow axle = drive for lift rotation.

The 24T gear on the grey axle has a disc which 4 holes around its circumference - two holes have axle /ball pins which would engage with a trip mechanism to block rotation at 180 deg intervals.

With white 24 T gear slipping the 24T gear still rotates activating the trip system, once trip de-activated and releases the lift, white gear drives the yellow axle again for another 180 deg. rotation.

Re Geneva Gear:
I have been hunting on line for a two arm version without luck but came a cross a 3 arm version - still hunting !

Another possibility is a Scotch Yoke / Crank device with built in dwell.

 

Hey Doug! I have tried using a retarding mechanism with clutch but I did not succeed in creating a version with a good timing and smoothness so I'm really interested in your progress!

[doug72]

3 hours ago, DaFokka said:

Hey Doug! I have tried using a retarding mechanism with clutch but I did not succeed in creating a version with a good timing and smoothness so I'm really interested in your progress!

I have made test rig of my idea and works but with a slight jolt as wheel starts to rotate again.

Here is a video which demonstrates how it works. Needs a lot of refining to improve it and made more compact.
Also find a way to lessen the jolt.

The blocking arm is normally down and stops rotation until the trip lever drum / lever mechanism raises it and frees the wheel.

The rotating arm uses the small turntable as I have plenty of them.

 

 

 

Edited March 7, 2017 by Doug72

[RohanBeckett]

great mechanism!

This should be able to scale up to a larger size (and operate a bit slower), and could be quite smooth!

[Captainowie]

You might be able to use a differential instead of a clutch gear. I made a mechanism that did something similar a few years ago.

[doug72]

1 hour ago, Captainowie said:

You might be able to use a differential instead of a clutch gear. I made a mechanism that did something similar a few years ago.

Can you explain how that works and what each axle is doing ?

[djm]

You may want to take a look at adapting the mechanism of torso's Cardan Lift GBC. It achieves two delays for each rotation, which would appear to suit the needs of your GBC.

 

Regards,

David

Edited March 9, 2017 by djm
typo

[DaFokka]

Wow, that's a lovely module! It would be interesting to find out if this solution could generate the torque and precision needed for the ballkirk wheel.

[Captainowie]

On 08/03/2017 at 7:05 PM, Doug72 said:

Can you explain how that works and what each axle is doing ?

Sure.

The red axle is connected to the motor and moves constantly. The disk and differential serve to intermittently route the motion to the blue and green axles alternately. For most of the time, the diff is prevented from rotating by the axle that's held up by the disk, so the path of least resistance is through the diff and out to the green axle. When the gap in the disk passes under the axle, the axle is free to rotate. Once that happens, the path of least resistance becomes the diff itself, which turns the blue axle. This relies on there being some load on the green axle.

In your case, you don't need the blue axle output, you just want the start-stop of the green output. It's then just a matter of gearing it right so that it stops twice per rotation. You could also put a second gap in the rotating disk to double the rate of stoppage relative to the rate of turn of the axle.

Does that make sense?