Sunday, April 24, 2011

Week TechVideo, 2011 #16 - Moving Targets

Likely you remember the first video from the LEGO FlexPicker, developed by Shep.

Shep is a mechanical engineer fascinated by this type of robots and since then he didn't stop doing improvements and expanding his model, making it running faster and smoother.

Finally this culminated into a 10ft (3m) long workcell, with four autonomous delta robots, capable of picking and placing colored blocks at a rate of 48 per minute. Each robot can handle 12 blocks per minute, meaning it can move one every 5 seconds!
The blocks constitute moving targets, fed by two conveyor belts moving at 100 inches (2,5m) per minute, which makes them not trivial to catch and sort.
There is a light/color sensor on each conveyor, which determines the blocks color and position into a chronological array. With this information and some mathematical operations, it is possible to calculate precisely the blocks position at each moment, and where the robots should pick each block.

The precise kinematics for the movements of the robots are dynamically calculated using detailed formulas that convert the Cartesian coordinates (x,y,z) of the location of the brick into the angles of the servo motors (theta1, theta2 and theta3) from each delta robot and vice versa. This is the heart and soul of the robots.

As the robot moves around, each motor speed is adjusted relative to the other motors speed in a manner that all three motors arrive at their target position at the same time. This makes all the movements very smooth and the robot doesn’t shake too much. The motor speeds are also adjusted so that the robot moves as fast as possible.

Since the blocks on the conveyors are always moving, the robot actually moves to a position where the block will be, rather than where the block actually is.

It looks complex. Right!?
A LEGO Technic and MINDSTORMS masterpiece, I'd say...

Here's the recipe, if you want to build yours...
  • 6 LEGO NXT bricks
  • 15 LEGO NXT servomotors
  • 6 LEGO NXT touch sensors
  • 6 LEGO legacy touch sensors
  • 2 HiTechnic touch multiplexers
  • 2 HiTechnic sensor multiplexers
  • 4 HiTechnic IRLinks
  • 5 LEGO light sensors
  • 2 LEGO color sensor
  • 1 mindsensors pressure sensor
  • 4 LEGO PF M-motors
  • 3 LEGO PF XL-motors
  • 4 LEGO PF IR receivers
  • 1 LEGO PF switches
  • 1 LEGO Train 9V speed regulator

For an extensive description about this work by Shep, visit the Tinkernology blog.

Tuesday, April 19, 2011

Behind the design of the Hurricane

After the publication of the Hurricane, the main question that came up was why the zero degree turning radius wasn't shown in action. The short and simple reason is because the model is not able to. Probably a big disappointment for many, and some might directly conclude that it is then a poor model design.
Could I have made it work? Probably so as 'Coney' has already proven with his Hurricane.
Would it have been technically as interesting? Certainly not! Sometimes with designing models the limitations of the LEGO building system become painfully obvious and this was certainly the case with this model. Several times I just wanted to cancel the project, as it didn't live up to my own standards and expectations, but decided to continue and see how far the jeep would get and explore the boundaries of what was possible. So what was the development process like?

Because the real Jeep Hurricane is a technical marvel, I wanted to design the LEGO version in a similar spirit. Of course the zero degree turning option with skid steer had to be integrated somehow as this is the unique feature and characteristic of the real vehicle. The challenge however was how to combine this with the 'standard' 4WD and 4WS. An option would have been to power the left and right drivetrain and steer each wheel independently, but because that was already done by 'Coney' I wanted to do something differently. The problem also with steering each wheel independently is that they easily end up misaligned, unless there are some electronics behind it like in the real Hurricane.

So my first question and challenge was if it would be possible to solve the problem of the different wheel configurations mechanically in such a way that all the wheels are related and connected with one another in all positions, not forgetting that they also needed to be individually powered and suspended.

For the standard steering mode, having the position of the left and right wheels connected with each other, the easiest was to use a gear rack.

I also knew that by moving the whole gear rack away from the wheels, they turn inwards. This had to be achieved by a controlled sliding motion for which again gear racks were used in combination with a worm wheel. A linear actuator could have done the job here as well, but they would have been too big.

Once there was a working prototype of one of the axles, I had to build another one, which was a great opportunity to see if things could be simplified and built more compact.

The next challenge was to find a solution for switching from normal drive to skid steer drive, using only one input. In any case it was necessary that the left and right drive train are separated, which should either work synchrone or in opposite directions. To achieve this the first idea was to be able to switch between odd and even number of gears in between the drive trains. Although there was a working concept it had certain drawbacks, one of which was the lack of a central differential which was not very realistic. So then the idea came up to use the differential itself as part of the switching function. Either power the central differential so both output axles go in the same direction, or power one of the axles as input and block the differential, so the output axle has to turn in the opposite direction. Because this meant that the smaller gears in the central differential play an important role and had to deal with some high stress I added another gear in the end to form a couple.

So now I had two working concepts, one for the different steering modes and one for the different drive modes. The next step was to integrate both in a single chassis. It was important to keep the distance between the front and rear axle as short as possible so it had the best chance of working. Preferably the model should be able to carry some motors too, which meant that space was very limited. Therefore it took some redesigns before I had solved all the interference between the different moving parts. Unfortunately this also meant that one of the differentials had to move further back, giving one of the axles more leverage to twist.

After the chassis with drivetrain was done, it was now time to connect the different steering configurations of the front and rear axle. The thought was again to use a switch for selecting a configuration and use a motor to put it in action. The central lever for switching the drive train in the chassis didn't leave much room for both a motor, and the switching function of the steering modes. Besides a possible misalignment, this lack of space was the final reason to leave out the crab steering mode. I still needed to reverse the direction of the input axles of the different steering modes somewhere in between the front and rear to make sure that the result was correct.

On top of that the drivetrain had to be connected to, a couple of V8 piston engines in both front and rear, which meant a lot of other gears and axles had to go through the center of the car as well.
With so many things depending on one another, a change at this point would have major consequences so from now on it was just a matter of fixing the center console together to see if the whole concept worked...

One could say that the concept was proven with all the different configurations, but unfortunately the model was not able to drive autonomous as I had hoped. Was this due to design flaws and could it be solved? Those were important questions before deciding on how to continue. After analyzing the model I concluded that there is some room for improvements, but that it will not be enough to make the model work autonomous with motors. In many cases I believe I ran into the limitations of the LEGO building system instead. Next time I'll explain the reasons why...

Sunday, April 17, 2011

Week TechVideo, 2011 #15 - City Hunter

Sunsky (Jaheo Jung) made a small city car for the 12th BrickInside Creation Contest. City Hunter his its nickname.
He has used several Technic soft axles of different lengths, to give the car some smooth surface curves and quite a distinctive look.

However I'd say the aesthetics part is not the unique or even the most distinctive feature from this roadster.
Despite its size, City Hunter still has some nice working features, like opening doors, one working two cylinder motor and the front wheels also steer of course.

It was exactly the steering function in a car this size, that required some innovation.
See the images below and look how Sunsky managed to make the wheels steer, without using any specific Technic steering parts.

Notice the center gear was raised by half stud, to fit with the surrounding gears.


Also a special note for the very small seats, which still present however some adjustments, as you you can notice from the images below.
The steering wheel is also adjustable, despite only seen from the video.

Simple, effective and adorable!

For additional images, you can look at Sunsky Brickshelf folder, or even more from the original City Hunter presentation page at BrickInside (although in Korean).

TBs TechTips 33 - Stewart Platform

Since we are now in April and quite far from the March LEGO Technic Challenge, dedicated to the "Linear Movement", we can now talk about topics somehow related, without fearing to influence contest participations.

So, lets take a look on the Stewart platform [1].
Such devices allow the ability to move other devices mounted on their top, over six degrees of freedom (namely the three linear movements x, y, z and three rotation movements as pitch, roll and yaw). They are a kind of parallel robot or parallel manipulator, controlled by six prismatic actuators mounted in pairs, crossing over to three mounting points on a top plate.
This platform was first designed and made operational by E. Gough in 1954 for industrial tire testing machines. Later it was described by D. Stewart (1965). Although commonly referred as "Stewart platform" it would be more correct and fair to call it "Gough/Stewart platform".

Besides six prismatic actuators, the Stewart platform also includes one lower base platform and an upper payload platform. It also uses 6 spherical joints and 6 universal joints, connecting the prismatic actuators to the respective lower and upper platforms.

Because of its complexity and difficulty to control, there have been several further developments looking for optimized geometries and easier control, however the original Gough/Stewart platform remains the most known and reproduced.
The geometric restrictions that applies to this setup, requires that prismatic actuators must move in a combination of movements articulated to each other, so-called synergistic motion platform.
The Stewart platform manipulator with its 6 DOF motion, is a complex system requiring deep knowledge on advanced mathematics in order to solve its equations and achieve full control of the platform. This is often refereed as inverse and forward kinematics, which applies also to other robotics domains and 3D computer animation techniques.
In our case, the inverse kinematics are mathematics treating the problem of describing the position and orientation of the payload platform in terms of the actuator variables, i.e. all the six actuator lengths.
The forward kinematics of Stewart platform determines the 6 DOF motions of the upper payload platform and the link length variables, which plays important role for the MIMO (multiple input and multiple output system) control or the motion visualization of the Stewart platform, but unfortunately it is difficult to come by because of the nonlinearity and complexity of the equations describing the system behavior. Hence difficult to achieve in realtime systems.

Most common uses of Stewart platform devices appears in machine tool technology, satellite dish positioning, telescopes, surgery devices, etc. The Stewart platform design is extensively used in flight simulation, particularly in the so-called Full flight simulator for which all 6 DOF are required.

As you may expect, there has been several who have tried to implement such platforms out of LEGO Technic. While some remarkable solutions have been designed, I have more serious doubts about the real achievements on their predictable controllability...

Above the barman (barebos) prototype. This is probably the first LEGO realization of a Stewart platform. It seems to work quite smoothly, but most likely this was a carefully selected sequence of movements (on the actuators), that won't lead into noticeable mechanical constrains.
The mechanical leverage that allows each actuator to extend the correspondent payload vertice, twice its own course, fits really nicely in a prototype like this.
You may find some additional photos and details of this realization, from Barry's folder on Brickshelf.

Here another Stewart platform realization. This one by Shep from Tinkernology blog.
As he admitted the movements fluidity we see in this video are totally faked. In the sense he has found first some working positions with a regular remote, and then mimicked them programing one NXT connected to an IRLink sensor, from HT.

By the time of the LEGO Technic Challenge raised last March, about "Linear Movement", there was a new set of Stewart platform experiments popping. As an example, this one by Laurens Gauwloos, had probably a strong inspiration from one of those above. However still worthy to mention.

And finally on a much more simplistic note, this motorized flight simulator by Jovlem (not really a Stewart platorf at all), using just three small linear actuators.
Really nice and effective realization, either from both technical, visual and demonstrative aspects.
Such configuration eliminates all the problems with mechanical constraints from a real Stweart platform implementation, thus over simplifying its control. Of course it doesn't allow real 6 DOF movements, namely pure roll and yaw movements (that's why real systems use much more complex setups) but it perfectly serves the intended purpose. This was another entry to the LEGO Technic Challenge from March.

Guess you're willing to make something similar...

Wednesday, April 13, 2011

8070 small alternate model, at LEGO Club

I've noticed via EuroBricks today, there is available from LEGO Club Building Steps page, one set of instructions to build a small alternate for the 8070 Supercar, as a Chopper.

Download them here. I've opted to post the direct link, as the path to get there seems a bit weird at the moment...

Sunday, April 10, 2011

Week TechVideo, 2011 #14 - Pilatus PC-21 trainer aircraft

Planes or aircrafts made out of LEGO Technic parts, is something quite unusual to see and difficult to create with a good appearance.

Maybe the most recent new parts will turn this a bit easier and we will see them more often.
At least, this is what Khan (Ismaël Juhoor) may lead us to think, after his fantastic Pilatus PC-21 trainer aircraft.

Very well done, full of details and plenty of sweet functions.

Among its features we have:
  • Dihedral angled wings
  • Detailed front cockpit
  • 5 Blades Propeller
  • Retractable 3-wheeled landing gear
  • Steerable nosewheel and rudder
  • Ailerons control
  • Elevator control with trim
  • Dual student/instructor controls for these 3 last functions
  • Ejection seats
  • Slotted flaps

Khan as also published some CAD representations of a few mechanisms from this aircraft, like the retractable and steerable nosewheel and ejection seats, at SeTechnic forum.

You may find a lot more photos with details about this model, at Khan's host, with names matching "pilatus*.jpg".

Finally, clearence to show images from the 8081, Extreme Cruiser ;)

After an image with watermarks from 8081 (Extreme Cruiser) that surfaced a few weeks ago, Toys'R'Us has finally brought us the first official images from the 2011 LEGO Technic set, best kept in secret...

These won't answer to most of the questions and hypothesis advanced in our previous post, but at least we can now confirm with certainty a minimum set of functions:
  • HoG front axis steering.
  • Opening rear and side doors, as well as the hood.
  • 4 wheel real suspension.
  • Dummy engine under the hood.

The site lists this set with a price of 49,99€ and says it is in stock. I've some doubts about this, but if it is true, it shouldn't take long until we get the first review online, and also get to know a bit more about this set's details.

If the "Limited Edition" yellow band on the box right margin really means some restricted availability, at least we already know where to buy this.

Biggest fans disappointment, seems to go for the fact that corner parts defining the windshield contour, "Axle and Pin Connector Toggle Joint Smooth" were not released in black again, but LBG ones were used instead.
AWD has been also claimed by some, but set reference number among the other sets released for the same half, uses to indicate the comparative box size within the portfolio and this, the diversity of functions introduced and price target set.
Don't think we are going to see a three diff setup, into a 50,00€ set price though.

Friday, April 8, 2011

TBs TechTOC 11 - Hurricane

Nathanaël Kuipers, just presented his latest Technic creation. Truly one of a kind!
It is a model from the no less fantastic and innovative, Jeep Hurricane.
Hurricane is a concept off-roader unveiled in 2005, at North American International Auto Show in Detroit by Jeep, a subsidiary of Daimler-Chrysler.
Among its distinctive features, this concept vehicle includes a couple of HEMI engines (one at front and another on the back), and several steering modes including the ability to turn itself completely around in place.

The first thing I realized was how the new 8110, Unimog U400 wheels, should fit nicely in this model, once they become available.

While Nathanaël reproduced most of the Hurricane details, like bumpers, seats, dashboard, each wheel independent suspension and aesthetics, this is nothing compared to the drive train which reproduces the several steering modes, apart from crab steering.
It is not the first Hurricane built with LEGO Technic, but most likely the first one with fully coupled steering control, delivering both "conventional" AWD with 4WS and Zero Steering with "Skid Steer" like, drive options.
The original concept from Daimler-Chrysler must use some sophisticated  electronics to control the wheels all-together and  keep them properly oriented to fit the active steering mode. On his model Nathanaël needed this to be ensured via mechanical links.
Somehow it turned too much complex to have the four wheels connected all the time and implement all the Hurricane steering modes at the same time. Thus the Crab Steering option needed to be drop.
Hence still some room for further innovation, ahead of you...

Notice the wheels on both sides, run in different directions (similar to Pivot steering, a Skid steer maneuver)
when the Zero-Steering mode is activated, in order to make the vehicle to turn over itself.

It is about minute 2' 10'', the show starts and we see a demo from the Zero-Steering functionality.
Notice the steering mode switch must be done with the wheels aligned straight (probably also the same as with the real concept model), otherwise something may jump out of its place...

Did you realize the solution found, to make both steering modes work over the same design?
Purely "Out-of-the-box Thinking" I'd say!

If you did not, definitely it won't be the bottom view below that will enlighten you. Despite often the most interesting view from a large Technic car, it seems in this case a lot of the interesting bits and mechanics are tucked away deep inside the structure and its layers.

As any AWD vehicle, this one also requires more than one differential as you can clearly see from the bottom view above (except the central one which has a different purpose). These allow for instance the wheels to run at different speeds while turning, control traction, etc...

Clearly the Hurricane is a 4x4x4 (Four Wheel Drive, Four Wheel Steer) class vehicle.
So lets dig a bit more on the original Hurricane steering features,as explained into the great HowStuffWorks website.

The Hurricane's steering system is a marvel of engineering all by itself. There are multiple steering modes using four-wheel independent steering. That means that each wheel can turn separately from the others.

In standard steering mode, the rear wheels turn in the opposite direction to the front wheels, which tightens the turning radius and makes for more accurate steering. In a second mode, the rear wheels turn in the same direction as the front wheels, meaning the Hurricane can "crab-steer" -- move to the side without changing the direction that it faces.

A third mode, utilizing the "T-Box Zero Steer" mechanism, allows all four wheels to "toe-in" and changes the drive direction to each wheel so that they alternate. The result? The Jeep Hurricane has a turning radius of zero. The Hurricane can actually rotate in place.

As you should be expecting, there is also additional information and tons of great photos, from other sources where Nathanaël uses to publish his models: MOCpages and Brickshelf.

So, was it innovative enough this time?

Just hope that Nathanaël would come now with a post from his own, to show the details how did he achieved this model.

Learn more about, at HowStuffWorks:
- How the Jeep Hurricane Works
- How Four-Wheel Drive Works
- How Car Steering Works

Learn more about, at Wikipedia:
- Jeep Hurricane
- Skid Steer

Monday, April 4, 2011

Week TechVideo, 2011 #13 - Tripod

Hispabrick Magazine 010 is out, and this month it features an interview with Menno Gorter, The Walker Dutchman.

As you can see, Menno's latest creation, the Tripod, has made the cover of this edition and in a special collaboration between Hispabrick Magazine, TBs and Menno Gorter, we are offering you an exclusive look at his work and especially this latest creation.

Below you can read an excerpt from the interview:

HBM: To start off, maybe you could tell us how you got started with LEGO:

Menno: There was LEGO in our house even before I can remember. My mother was a kindergarten teacher and fortunately she soon realized the great educational value of LEGO. It teaches you to think systematically, spatially and problem-solving; I can sincerely recommend it to all of you! Only then I had to share everything with my two sisters and brother. Later on we got electric motors and rails – that must have been my father’s input; he was a civil engineer. By the time I was twelve I already earned some money and I was the only one in the family who spent his own money on LEGO, and eventually all of it ended up being mine as I was the only one who continued using it. I’ve never really had a dark-age; the way I used LEGO was not usually considered childish and that kept motivating me. I did have a period when I felt I was the only one to still “play” with LEGO (I keep calling it playing, because playing with LEGO is fun… [2] ). That lonely period lasted quite long, until about halfway the 90s when I got in touch with De Bouwsteen, a then still small LUG. Ironically the first thing I was asked by this LUG was whether I was a builder or collector. When I explained what I did with my LEGO the reply I got was that I was neither of those. There were no members then who used Technic the way I did.

HBM: So when did you start with LEGO Technic? Your oldest walker on BS is from 1979!

Menno: I built my first reasonably working LEGO walker in December 1972, only I didn’t make pictures of my creations back then. I did already have LEGO motors, but in 1972 I got one of those sets with gears, universal joints and tread links and that opened up a whole new world of possibilities for me! In short, it was a construction that had something like the push rods of a steam engine and as a result it did not so much roll as walk with a walking frame. Before that I had tried something similar with the white turntables on the red rims that were available then, but the result was not what I wanted. Later on I have even created six-legged walkers with really old LEGO. There were so many more possibilities after the introduction of LEGO Technic! That’s the kind of walker you can see in the 1979 picture in my BS folder.

HBM: LEGO Technic has changed a lot over the years. To what extent do those changes affect the way you build your models?

Menno: If you were to step straight from the time of the 850 into present day Technic you’d probably not know where to start It’s simply a challenge to make the most of what you have. During my time in MPD (the NXT beta test program) some complained about the rough shapes of NXT motors and sensors. I looked at it differently. Instead of building that big motor into something you need to use it as a starting point and attach things to those motors. It’s hard to find more sturdy elements! New elements mean new possibilities.

HBM: Some people say it is a pity there are no better pictures of those creations and it is virtually impossible to see any construction details. Why is that?

Menno: I don’t like to show technical details. You need to be able to see something works, but not exactly how – people will spend more time watching models that way. Additionally, I believe that if you want to learn something you shouldn’t simply copy or follow building instructions. I am absolutely against the current ‘cut and paste’ culture. And to make things worse there are even people who claim those copied constructions as their own. Another reason is that I spend most of my day working with photographs. Since 1996, photography is an important part of my job, so at home I’d rather build than take pictures. Anyway, when I did take more detailed pictures people were always asking for video footage and I suppose now they’d want building instructions… I do make videos now so people who cannot come to any of the events I go to can see my creations in action.

If you want to read the rest of the interview you can also download Hispabrick Magazine for free or read it online.

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