GBC Square Drive Module,s

[doug72]

5 hours ago, Thierry-GearsManiac said:

In order to eliminate (or at least to mitigate) the falling balls problem, would it be a solution to replace the cradles' outer fingers by walls = kinds of "armrests", like in the original design ?

On my side, I think I should take up the challenge of building a one-high-speed-cradle variant (without reverser of course, and with the goal to test my horizontality mechanism in real conditions), but I expect a lot of falling balls anyway !

 

I,m still finding lost balls in my Lego room its amazing were they roll too !

The sides on the ball cradle can only be 2L high otherwise it will snag on the underside of the inpout loading box.
At the dischargs point if too many balls on the cradel they tended to exit sideway and through the centre of the 4 x 7 frame.

A 7L axle through the frame mid point works OK with 2 half bushes to keep it in place.

Good luck with your version and ball hunting !!

 

[Thierry-GearsManiac]

Here is my (very slow) beginning :

First test of the core mechanism, 20*14 frame, with the bevel gears-based arm :

Because of the thickness of this variation, I had to recess it into the rectangle while giving the sprockets a double-sided support and preventing the arm from colliding the tread.

By chance, the tread length fits perfectly without the need of a tensioner.

Unfortunately, the whole arm is too short and reverse-folds itself when almost fully extended. Therefore I reduced the height to 12 studs (but a tensioner is now required).

Here is a quick-and-dirty height test (after building a cradle as well) :

Unfortunately, there is too much backlash that may later prevent a reliable alignment between the cradle and the pickup area :

• rotation backlash caused by the bevel gearing
• twist backlash and forearm flexibility because of the single-sided support of the gears

I therefore plan to give up on recessing the mechanism, to dismiss the bevel gear solution and to revert to the 14-stud height : I already rebuilt enhanced versions of the spur gear arm system and the folding rhomboid chain, only 3-stud thick and with proper bracing (i.e. double-sided, thanks to half-thickness beams/liftarms or specific axle-and-connectors build) : coming later...

Edited February 24, 2022 by Thierry-GearsManiac
Backlashes explanation, URL fix

[doug72]

@Thierry-GearsManiac

A good start :-

During my build It was a case of two steps forward, one step back at times until I finally achieved a reliable GBC module.

Would this work -?  there is no back lash between gears.
 The arms are very flexible. and 5L beams are used to tie the pairs of gear arms together and only 2L thick.

IMG_8546

IMG_8547

I am currently developing a new GBC Train Side unloader.

Edited February 18, 2022 by Doug72

[aeh5040]

This is a very interesting project!  Could you use a parallelogram linkage instead of gearing, like a Schmidt coupling?

[Thierry-GearsManiac]

@Doug72

In your proposal, there seem to be too many degrees of freedom, so that the joint holding the cradle will be able to rotate freely on some range of angles. it's almost like having two successive standard hinges (i.e. three bars) instead of geared hinges (although the kinematics are slightly different).

You can try it by attaching the center end on a stand and manipulating the other end with one of your hands.

@aeh5040

Parallelogram linkages (i.e. two in series) could have done the trick as well : I've already thought about them.

But if one wants to prevent the parallelogram from turning over (and failing by getting crossed in the absence of a 3rd link like in Schmidt couplings), then the center point would have to be outside the rectangular tread and the two arm segments long enough.

A Schmidt coupling could indeed work, but because it constrains the input and the output to be single-sided and on opposite sides, it would result in a rather bulky build : from the rear to the front, there are : 1. the input stand holding the input "star" ; 2. all the intermediate parts of the coupling ; 3. the output "star" ; 4. the tread (traversed by the axle joining the output "star" to the cradle) ; 5. the cradle ; 6. a stand holding the frame of the tread drive (otherwise it would float in the air !)

Instead, if some Schmidt coupling flavor is still desired, one could still design a hybrid arm system where the "arm" would be the first half of a Schmidt coupling and the "forearm" would be any single geared arm segment flavor (spur gears, chain etc...), so that the output axle can now extend on both sides (to the cradle in front, and to the tread behind).

[doug72]

@Thierry-GearsManiac

This might work for the rotating arm connecting the centre point with the  track link that attaches to the ball cradle.
The rack slides freely in and out without use of multiple gears and without any flexing.

LEGO Housing 2 x 15 x 3 for Gear Rack (18940) & LEGO Gear Rack 14 x 2 with Groove and Connectors (18942 / 60578)

I will build a test rig to see if it works OK.

[doug72]

Work in progress.

Test Rig showing the rotating arm at maximum & minimum positions.

Arm rotates freely around the sprocket wheels - Track tensioners would be required

Ball cradle would be attached to end of the arm.

IMG_8549

IMG_8548

Edited February 22, 2022 by Doug72

[Thierry-GearsManiac]

OK, but this arm alone won't prevent the cradle's axle from spinning with respect to the frame.

 

On my side, slowly working on my prototype, I managed at last to make a video of it in action, using the geared arm variant (rebuilt with Z36 gears only) :

https://diode.zone/w/aNr5BcPZWSpTCHq2VeYzCk

I just noticed I forgot to show how impossible it is to tilt the cradle (at least beyond the backlash), but the moving of the passive gears speaks for itself. The bar supporting the minifig shows the circular translation of the elbow gear.

 

[doug72]

@Thierry-GearsManiac 
 

Well done

An intriguing & mesmerising mechanism that looks to be very reliable. I can now understand how it works.

I like the Mini figure, perhaps he should be wearing a Hard Hat !!!

I have enough Z36 gears to build it.

Could you post a close up image of the Z36 gear train ?

==============================================

Meanwhile I have added a cradle to my latest version which required track tensioners.

The cradle remains roughly horizontal by gravity around the track and ball cradle can carry 9 balls OK.

[Thierry-GearsManiac]

For the Mini figure, I unfortunately own very few of them (including accessories).

Here is a close up picture of my current mechanism :

(removed from the module, rear view ; the black 4x2 L-shaped liftarm was attached to the frame ; a few extra #44 connectors nearby = the parts used for the elbow)

In my build, the spacing between the axles of adjacent Z36 gears is 4.5 studs (or here, approximated by the hypotenuse of a 4x2 right-angled triangle). Therefore each arm segment is 9 studs long, and the maximum allowed radius of the unfolded arm must stay below 18 minus a few studs (i.e. never undergoing a 180° angle).

 

However, your drive mechanism design is much bigger : the half width and height of the square traveled by the cradle pivot is 12 studs (frame), plus approximately 4 studs (distance between a sprocket's center and the pivot mounted on a tread link passing on it). The biggest distance from the cradle's pivot to the center is therefore 23-24 studs, which means that you'll have to either build a very much longer arm system (i.e. more than 12 studs for each arm segment = more than my bulky turntable-based early prototype), or reduce the size of the drive mechanism.

Therefore, if we keep its size as-is, in order to increase the length of the arm segments, one must either :

• add extra idler gears, at the expense of a slightly higher backlash. For example, adding two Z20 gears per arm segment would increase their lengths to 14 studs.
• (EDIT20220224 : use the (big) "splat" (a.k.a. "flower petal") gears, hoping that their higher/worse linear backlash will be mitigated by their bigger radius/diameter, keeping the angular backlash low enough on the end gears. The other big gear families ("Expert Builder" and "Samsonite") probably have the worst linear backlash).
• switch to the folding diamond-shaped (or rhomboid) chain solution (I plan to show it in action in an upcoming video), because the upsizing is only a matter of adding chain (or tread) links, which doesn't increase the backlash ; the only challenge is to adjust the optional tensioners.

 

On another side, your use of the sliding rack (a pair of parts I don't own yet) does give me some extra ideas : trying the telescopic shaft solution (or even the use of the sliding Z8 pinion (11955)).

 

Edited February 24, 2022 by Thierry-GearsManiac
see text

[doug72]

Square Drive GBC using sliding arm with Video.

Test Rig now built to prove a sliding arm functions as desired..

Driven by an XL motor with speed controlled using a PF train controller.

Track tensioners added to prevent track slapping but there is still sight jerkiness of the track as it moves due to using the small sprocket wheels.

Would be much smoother if the large sprocket wheels were used.

Ball cradle can carry 9 balls per circuit but could be widened to carry 12 balls

Structure needs to be improved to to give clearance at the ball loading input point at the bottom left using a GBC compliant input box.
Unloading point could be any where on the right side to suit ball discharge to the next GBC module input at 10L height.

 

 

Edited February 24, 2022 by Doug72

[doug72]

1 hour ago, Doug72 said:

 

Edited February 24, 2022 by Doug72
Duplicate post removed

[Thierry-GearsManiac]

As seen on your video, the stiff telescopic rack does still improve the reliability by stabilizing the cradle, more precisely by reducing its pitch (back-and-forth tilting) and yaw (left/right turning), despite the weight of the cradle and its load, and even in the absence of gear-based permanent roll (i.e. side tilting) control.

The stiffness of the arm also plays an important role in both of our design variations.

The only critical point that has to be solved (already solved in your previous design) is the roll cancellation at the entrance and the exit, thanks to a wall on the outer side and a funnel-like guide on the inner side (on the input structure).

[doug72]

@Thierry-GearsManiac

Thanks for your comments

I have now eliminated the sag of the track between the two top sprockets by adding some horizontal support beams.

Next step is to raise the structure so an input loading box can be added.

Might require some side guide beams

Now studying your method and I think I have all the parts required to build it.

Edited February 24, 2022 by Doug72

[doug72]

Further improvements made:-

Frame adjusted to be vertical.

Ball cradle swing is minimal but an upright beam added with taper to ensure cradle lines up OK at the ball discharge point.

Other upright beams on LH side installed to correct any swing of the loaded ball cradle.

Ball Cradle can now carry 12 balls per trip, 5 trips equal 60 balls.

Next step, build the loading and unloading boxes.

IMG_8552

Edited February 25, 2022 by Doug72

[Thierry-GearsManiac]

On my side, here is the video of the "rhomboid chain drive" passive arm in action :

https://diode.zone/w/89d1z9XTv6yCJRfXFx6Ay6

The arm segments are 10 studs long (spacing between the centers of the axles).

Built using half-thickness beams/liftarms (in order to stay at 3-stud thickness), they are slightly stiffer than an axle-and-connectors build, reducing pitch and yaw for the cradle.

By chance (again), the chain didn't require tensioning gears (although I provided room for them, using triangle liftarms) and therefore exhibited no backlash ==> (almost) no roll.

 

Tests with big gears pending :

• "Expert Builder" gears do in fact have a very low backlash : 1/2 tooth for 4 meshings from one end to the other, thus a very low angular backlash. (for information, the modulus is 1/3 stud, i.e. the tooth length on the pitch circle is pi/3 = approximately 1 stud)
• "splat gears" experiment not yet built, only quickly tested. With a modulus of 1/2 stud and using the biggest possible gears (Z14) as end gears and idlers, the whole arm length is no more than 2*14 = 28 studs when unfolded at 180°. Aesthetically speaking, these gears could be used for giving a "kid's toy" style to the device (one could build the frame as a wall of bricks of a single color, typically white, but I don't have enough of them)

That's why I prefer to finish building of the module in its current form...

[doug72]

Square Drive GBC with single arm.

Now dismantled.

 

 

 

Edited April 7, 2022 by doug72