CAT 573C Feller


LEGO takes up space.  We all know this, and yet we still seem to try to cram as many working functions into a MOC as we can.  Sometimes it works out well.  Sometimes we have to scrap a few functions.  Other times, the functions are so dense you really cannot believe you got it to work.  This is the story of my wheeled feller.

The full Gallery may be found here. Instructions may be purchased for $5 USD.  Buy Now Button

CAT 573c Feller

I have been thinking about making a feller for about two years now.  It is a project I have never seen done before, with the exception of two tracked fellers (OK, and my other one).  Over this time, I have been planning, acquiring parts, and making plans, and over the last four months I have been building.  Nothing I have made has been so complicated or so dense.  There is no space left.

As I always do, I stared with the dimensions of the vehicle.  The schematics for the CAT 573C were easily available, so I stared with the chassis.  I knew space would be an issues, so the driveline had to be simple and compact.  The Power Functions XL motor would be geared down 3:1 and mounted just behind the rear axle.  A drive shaft would move through the steering pivot to the front axle.  The rear axle would have simple pendular suspension.  The steering would be completed by two linear actuators placed on either side of the pivot with a PF M motor on top.  Simple enough.

From here, things got complicated quickly.  The MOC would have four remaining functions.  The feller saw, the grapple arms, the feller tilt, and the feller lift.  Since trees are rather heavy, fellers are designed with as many of the system mechanics behind the rear axle.  As such, all of the functions I would add would need to be in the rear, as the front would not have any space.  I quickly learned this would not work.

Eventually, I found what would fit.  The IR Receivers would make up the rear bumper, and the battery box would be directly over them, off to the left.  Two PF Ms would be on the right and would drive two mini Linear Actuators.  These would move two pneumatic valves. These pneumatics would move the lift function and the grapple arms function.  An air tank would supply the pressure from a pneumatic pump placed on the driveline.  Another PF M would be placed over the front axle to give the feller head the tilt functions (it should be noted, 7 designs, and five weeks were spent on this feature alone).  The final PF M was in the feller head, and would drive the feller saw.

After packing, repacking, and packing again, all the features we set.  Then all the cabling and hosing were placed.  No easy task, as I was running out of space, and 25 or so hoses, and 10 cables take up a lot of room.  I added some comfort features to the cable, including a (half) chair and a roll cage.  And so Mr. Technic could get in, a little step.  Then a lot of paneling for the rear, including some access doors on the rear, and the model was done.  Here it is in action.

As you can see in the video, the MOC worked well, but some of the functions did not work as clean as I would have liked.  The drive and steering were fine, with an easy drivability.  There was a lot of mass in the back, so sometimes the torque from the drive motor would cause the back to tip.  The saw worked well enough, and for the most part so did the tilt, but the pneumatic lift struggled.  It was a little overloaded because the saw unit was too heavy.  The grapple arm worked well, but for both pneumatic rams were hard to control.  As always with LEGO pneumatics, they too often are off or on.

Until the next MOC, happy building.

Talon Track


Every once and a while I see something so creative I have to build something like it.  I happened with my HH-65.  It happened with my Zil 132.  And to some extent it happened with my Spitfire.  But when I saw the Urban Buggy from Chrismo, I though I have to make something like it.  It was such a fresh and creative design.  It had such great lines, a perfect stance, and a unique driveline setup.  But while imitation and outright plagiarism are the most sincere forms of flattery, I thought something of my own design would be a better contribution to the LEGO community.  I present my Talon Track Car.

You may find the full gallery here, and the instructions here.

I designed this car to be fast and stable, just like a track car.  I started with a drivetrain that would be reliable and effective.  A PF XL for drive, and a PF M for the steering.  I placed the PF M in the front mounted directly on the suspension unit, with a return to center spring in the middle of the mount.  The system is set up differently than in my Rumble Bee, but uses the same return part.  Each suspension arm would have a single shock absorber.  Directly behind the steering motor was the XL for the drive.  It was geared up with a 20z/12z ratio, with the driveshaft connecting directly to the 20z gear that turned the differential.  The rear suspension used an independent setup that was developed a long time ago for my Red Car Bigger (great name, huh).  If it’s not broke, don’t fix it.  The suspension was planted.  I placed the rechargeable battery box and the IR receiver behind the rear axle.

The car was quick, and didn’t have any problems, but faster would have been cool.  The return to center system worked well, especially for the quickness of the car, and the quickness of the steering.  It was easy to control.  The car was robust, and crashed well.  So go ahead and build your own.  Enjoy.

Spitfire Mk IIa


I am not a very ambitious person.  Sure I made it through college and graduate school, and have managed to work well in job for a while now, but for me to do something challenging, takes a lot of convincing.  It doesn’t happen often.  This project was a little bigger than it should have been, and I got in over my head.  This is not the first time this has happened (1, 2).  The project was interesting enough for me to keep moving forward, even after six months.  I present my 1:12 scale Spitfire Mk IIa.  I hope you enjoy the work.

View the full gallery here, and the work in progress gallery here.  Flickr set is here.

Spitfire 3/4

First, the whole reason I did this project was because of the excellent Baby Twin Otter of Cpt. Postma completed two years ago.  If you have not yet seen this creation, take a look at the above link.  When I first saw this model, I went home a made his variable pitch propeller   This was the first step to my Spitfire, though at the time I did not know it.

I chose to do the Mk IIa version Spitfire for a couple of reasons.  First, the model had to have a three blade prop, because I wanted to use Cpt. Postma’s design.  Spitfires stopped using a three blade prop somewhere in the middle of the MkV series.  Second, I wanted to model a eight gun variant, rather than the cannon variant because I think it has a cleaner look, and I love the red and yellow leading edges on the eight gun variants.  Finally, while it would have been great to do a early model Spitfire with the dark tan camouflage  adding both the dark green and dark tan would have been too expensive, and even more ambitious.  I found a number of pictures of a certain MkIIa with all the features I wanted.  I chose a Spitfire flown by Lt. Tomas Vybiral, who was a Czech pilot with the French Air Force.  The plane was Spitfire P8081 when he flew for the British in Squadron No. 312.  It had simple markings for me to recreate, a camouflage pattern I would be able to do (read afford), and I found some good documents to help my modeling.

Next came the internal planning.  The Spitfire would have working ailerons  flaps, rudder, and elevators (with correlating pilot controls), prop, prop pitch, V-12 engine, and retracting landing gear, all within the 1:12 scale.  Once I had the dimensions calculated, I started placing things in a simple “placeholder” model on my floor.  I constructed the engine, the propeller spinner, pedal/joystick assembly and placed them in the placeholder.  Then I made the placeholder 3D.

It took two months to get the rest of the internals all set.  The required moving various parts of the 3D placeholder, and adding additional parts.  The joystick is connected through various liftarms to the rear elevator, and by axles to the ailerons   The pedals connected though a shaft to the rear rudder.  You can see the gears on the rudder.  The flaps have a simple lever in bottom left side of the cockpit.

The rest of the functions are controlled via Power Functions.  The small 8878 battery box is placed behind the cockpit, as is the IR receiver.  A PF M is housed under the V-12 and drives four mini linear actuators for the landing gear.  It is strong and simple, and works well.  It does not have the correct Spitfire landing gear geometry, but if someone can figure out a way to do it at this scale…well, I can’t figure it out.  A second PF M is used to power the propeller   It is placed directly behind the V-12.  Finally, a third PF M is placed behind the V-12, and works through a system of gears to power two mini linear actuators to move the pitch of the prop.  It’s messy inside, but it has everything I wanted.

After the internals, I had no idea how hard the rest of the Spitfire would be.  LEGO, you need to make more parts in Dark Green.  I know how selfish that sounds, but it would have been more helpful.  Thank to some newer sets, like the 10226 Sopwith Camel, and the  21016 Sungnyemun, it made it much more possible, but still limited me in many places.  I spent the next four months acquiring parts, and placing small plates over the rest of the plane.  With some help on the roundels from Dieterr89, it eventually came together.   The bodywork took a long time.  Too long.  And the lack of some parts in Dark Green forced me to make some concessions.  The canopy frame should be all Dark Green, but it was not going to happen with what is available.  The camouflage is not as clean as I would have liked, and there are some abrupt steps where some plate limitations made the transition for one part to another not smooth enough, such as on the rear fuselage.  Also, try as I might, I could not get the leading edge of the wing to be perfect.  The dihedral did not help either, nor did the yellow leading edge.  Also, the gaps between the control surfaces and the fixed part of the wing and stabilizer was more than I would have liked.  But this has happened before.

I am please with how it turned out, but there are some parts that I wish would be better.  I never seem to remember this when I start a project in this scale, but free moving functions just do not operate well as you hope when you keep adding parts.  The control surfaces work, but they could be smoother and lighter.  The powered functions worked flawlessly. I was very please with the way the markings turned out.  They are not as flush with the plane as painting would cause you to believe, but they make the Spitfire clearly identifiable.

My father would always tell me “never say never,” but it may be a long time before I do another large plane.  But I guess I said that back in 2008.

I hope you enjoy.  Thanks for reading.

International FTTS


It has been a little quiet in Thirdwiggville for the last month.  I have been working on a project that is taking a lot of time and resources, so my posts have slowed, even though my building has not.  But just wait, it’s going to be awesome.

Last summer I wanted to do another Trial Truck that would utilized some features I have never used before.  I wanted something complicated to see how it would work.  I wanted a model that would use four wheels steering, independent suspension, and have a simple two speed gearbox while being low to the ground.  After spending some time at the Chicago Autoshow, I saw a FTTS concept, so I thought this would be a great vehicle to model for this next truck.

This model would be built around an independent suspension.  After seeing it used so effectively in a truck by ATRX, I wanted to give it a try.  Each of the four wheels would use a simple double a-arm set-up with a wheel mount attached at the outside.  The wheel mount would house the portal axle and connect the steering linkage.  After a couple of different designs, I also decided the wheel mount would also connect the the shock absorbers.  This was a little unorthodox, as most independent designs mount the shock absorbers directly from the frame to the a-arms.  I did this for two reasons.  First, the model would be heavy, and I could not get the support I needed when the shocks were connected to the a-arms.  Second, and most importantly, I noticed too much suspension flex when the shocks were mounted to the a-arms.  The force applied to the wheel would go up the wheel, to the wheel mount, through the pivot, halfway down the lower a-arm to the shock.  LEGO is relatively stiff, but all these steps complied too much flex.  I would not have it.  I mounted the shocks on the wheel mount, and created a simple MacPherson strut set-up.  This worked well, as it allowed for full steering movement, long suspension travel, and adequate support of the truck.

The front and rear suspension axles both had a PF-M motor driving the steering.  Each were on independent PF channels connected to a single 8878 Battery Box to allow for individual steering, crab steering, and to solve steering drift commonly problematic with four wheels steering vehicles.  Both axles were connected with dual drive shafts running the length of the truck.  One drive shaft would then connect through a simple two speed gearbox to the PF-XL motor.  The final gearing was 1:6.2 and 1:10 for the truck.  This gave the truck sufficient top speed, with an effective crawler gear.  The Battery Box used for the drive motor and the gear shift motor was placed directly behind the front suspension, and in front of the drive motor.  This placement was perfect for stability.  It helped give great traction to the front wheels, kept the center of mass low and to the center with a slight forward bias.

I then finalized the model with a simple removable body built on a Technic frame.  While the hood was little high, and the rear body a little too short, it looked pretty close to the rear FTTS.  Fans seems to like the look, as it is still one of my more popular model.  See the full gallery here and the Work in Progress gallery here.

The model was a lot of fun to drive, and due to its squat design, it was very well planted.  The truck did not want to role over.  I think it could have used a little more suspension travel, and having four wheel steering was crucial to give it some maneuverability that was lost due to the suspension design.  The gearbox was flawless.  The truck did have some trouble skipping gears at the portal axle.  It seemed to happen when a single wheel was over-stressed as the driveshaft could have used stronger bracing in each suspension unit.  This placed a lot of strain on the particular wheel.  So would I do the independent suspension again.  Maybe, but it would need some strengthening and redesign.  Maybe it’s time for another truck like this.

Thanks for reading.  Something big is coming.

CAT D5K


Construction equipment was pretty much designed for LEGO Technic.  I learned this while designing my MB Axor Refuse Truck.  Yellow bricks are pretty popular and accessible, the equipment usually has many functions which can be replicated, and working models with power functions can be made to reenact various construction projects for great playablility.  After finally getting some large track links, I figured it was time for me to do a bulldozer.

I wanted to model the CAT D5K for a couple of reasons.  First, it used a two wheel track for each side rather than a three wheel track for each side.  Second, I wanted to do something by CAT.  Third, I decided on the D5K because for dozers of this size I think it looked the best due to its stance and overall balance.  Plus, when I started looking at the scale of the dozer I was to model, I learned the D5K would work best with the parts needed such as the tracks and blade, and work with the internal space allowed.

The base D5K really only has three functions: drive, blade lift, and blade angle.  I had no intention to add a ripper, because, frankly, I ran out of space.  Space became an issue very early.  I had 9 studs to work with between the tracks, and I needed to add four motors, a dummy motor, a battery box, and two receivers, all while retaining the appropriate look.  All the gearing had to be compact, and the linear actuators needed to be placed efficiently.  The real D5K has a manual adjustment for the blade pitch, but all of my designs left something more to be desired, so I took it out.

Both tracks would have their own motor, and I wanted to link them to a dummy engine, which required a differential.  I connected the motors directly to a worm gear which drove a 8z gear.  This gear was on the axle for the rear drive wheel, and connected on the other end to a differential which connected both drive wheels.  This differential functioned as a power take off for the dummy motor in the front of the bulldozer.

Two more motors were placed under the dummy motor.  One connected though a 12z/20z gear reduction for the blade angle.  It proved difficult to supply power for the blade angle function through the blade tilt pivot without taking up too much space.  The second motor was used to adjust the blade height.  After a simple reduction, two mini linear actuators were used to move the blade up and down.  It worked well, and was plenty strong.

I added the battery box under the driver’s seat, and placed the two IR receivers in the top of the cab.  It was not optimal aesthetically, but it seemed to work well for control.  And again, I just ran out of space.  I worked on the body, gave the model a working hood, and built a cabin.

The model worked well, but building with tracks is always a little bit frustrating.  Like it or not, LEGO plastic will never be fully smooth, and this is compounded with the track system.  Also, I found that the dummy motor would lose its connection to the drive wheels, as the axles connecting to the differential would slip out every once and a while.  This seems to be a commom problem with Technic builders, so we will see if the new axles will help.  I liked the size of this model, and it had a good amount of functions.  Now I need to use the tracks for something else.

Maybe another tank.

The full gallery may be found here.

Freightliner M2


For some reason, I often find myself building two trial trucks at the same time.  While I was building my ZIL 132, I also wanted to try something with floating axles.  The model would use 6 wheels, a 3 speed transmission, and fully suspended live axles.  I also wanted to model the Freightliner M2 Business Class truck as closely as I could.

The model started as my trucks usually do; with the axles.  The second and third axles would be identical, and would be connected with a simple pulley wheel universal joint between the two.  To keep the speed through the universal joints high, and the torque low, I used as 12z/20z gearing after the universal joints, then the knob wheels to rotate the axis, then the normal 8z/24z gearing on the portal axles to finalize the drive.  This also allowed me to keep fewer knob wheels as the second axle had the drive shaft from the transmission pass uninterrupted to the rear wheels.  The final drive ratio for the two rear axles were 1:5.

The front axle was a little more work.  I wanted to have the steering motor mounted on the axle so I would not need to have a steering shaft connect to the front axle.  This proved too difficult, as it would raise the PF XL motor that I was going to use for the drive to high on the truck.  I decided it would be better to mount the steering motor on the frame and connect to the front axle via a CV joint.  Once I made this decision, the front axle became easier.  I used a 1:3 gearing on the portal axles, a knob wheel, and then a drive shaft back to the transmission.  The steering axle would exit just above the drive shaft on the axle to move to the right for the steering motor.

The frame was pretty simple.  Once I had the transmission placed, and the axles spaced, it was simple to place the suspension components, and the shock absorbers.  Each axle had two steering links mounted vertically which connected to a 3×5 liftarm which would activate a shock absorber; very much like Lyyar’s design.  Each axle had a steering arm to keep the axle from swaying laterally.  Finally, all three axles had a number of 9L links to keep the various movements maintained.

The transmission was going to be placed behind the PF XL motor which was under the hood.  The changeover mechanissm would be placed in the center of the truck with the changeover motors mounted longitudinally, on both sides of the truck.  The PF XL motor was place directly above the first axle, and was mounted on a moving frame that was moved by the changeover.  This allowed a moving frame to work its way through the three gears.  The ratios were 1.25:1, 1:1.25, and 1:2.  This allowed for final ratios of 1:4, 1:6.25, and 1:10, which was more than capable for most terrain.  The drive and steering Battery Box was mounted over the second and third axles, and the gearbox 8878 battery box was just behind the changeover in a little box on the bed of the truck.

Finally, like always, a simple body was mounted.  I had a little trouble getting the look I wanted on the front of the hood, as the suspension components kept getting in the way.  I added a bed, covered the changeover and motors, and a couple more details and everything was finished.

The model was not my best driving truck, as six axles do not want to always work together.  The suspensions was supple, and I was getting no drive or steering input on the suspension.  The truck worked well over various terrain, but struggled on some on step obstacles.  The transmission mounting worked well at changing gears, but gears did not have a strong support, and I found they liked to skip at times.  I liked how the suspension worked, but I do not think it brought enough of a valued to use this system again.  It had moderate improvement on dealing with terrain, but it placed a lot of stress on a number of parts, such as the frame, the axles, the driveshafts, and the universal joints.  The next truck will use a pendular set up again.

The full gallery may be found here.

Power Functions 4×4 8081


For most LEGO enthusists, when they purchased the set 8081, they quickly modified the set with a Power Functions drivetrain.  It makes sense.  LEGO models are a little more exciting when they are motorized.  But I guess I went a little backwards.  I wanted to do the fun stuff first, and make the most complicated and compact drivetrain I could make.  I posted the instructions here, and they can also be viewed on Rebrickable.com.

But the comments kept coming from people who wanted to see my model motorized.  So I thought it might be a fun addition.  I added a two PF M motors, a 8878 Battary Box, and an IR receiver.  I tried to keep the modifications simple, so I could easily add the motors to the MOD, and take the system out if I wanted to.  The drive motor was placed on a simple mount that connected to the frame.  The power was fed thought a 8z gear to a 24z gear which then connected directly to the V8 driveshaft.  The driveline was unchanged from the V8 down.  The steering motor was mounted laterally in front of the rear seats.  A 20z double bevel gear drove a 16z gear, then a worm gear moved the final 8z gear which was mounted on the existing HOG steering axle.  I removed the passanger seat which is where I placed the battary box, and created a simple mount for the IR receiver.  The added weight required a new shock absorber, so I added that as well.

The model worked alright.  The drivetrain did well to handle the new power, and I could easily control the Crusier.  The steering motor was a little too powerful for the upside down facing steering rack.  It skipped a little under load, which was a problem over rougher terrain.  The drive motor was a little taxed, so a PF XL would have done a little better.  I guess I could add that, but I am ready to move on to my next model.  Stay tuned.

The full gallery may be found here.

Mercedes Benz Axor Refuse


I am a big fan of garbage trucks.  For some reason I find the combination of a smaller truck,with many features all with a complicated compaction device is a great basis for a complicated LEGO Technic model.  Plus, trucks are fun.

The hardest part was going to be the rear compaction device, so that is where I started.  I decided to use a Geesink Norba design as it would give me the largest opening for the trash in the rear because the mechanicals would be on the bottom on and the top of the opening.  13 studs wide is not much space.  In addition, this would allow me to have the rear hopper pivot up to let the trash out when it was full.  I would need to have three functions going though the pivoting hopper.  One at the pivot, and two connecting at the base when the hopper was closed.

The dumpster lift would be driven through a knob gear when the hopper was closed on the bottom.  The compation device would be operated with a gear on the bottom and a mini linear actuator on the top.  This mini linear actuator would also function as the opener for the rear compactor.  All the motors would be housed on the bottom, with one motor placed next to thebattery box.  The extractor would be operated by another mini linear actuator using a scissors mechanism to move the ejector plate.

The chassis was constructed with a PF XL in front of the steering axle.  The motor would power both the drive, and the extractor changed by a changeover.  The steering motor is placed on the right of the truck.  On the left, another PF M motor powers both the dumpster lift and the lower hopper compaction device.  All power came from a 8878 rechargeable battery box, through two PF IR receivers, and powered four motors: One XL for drive and the extraction plate, one M for steering, one M for the dumpster lift and lower compaction, and one M for upper extraction and hopper opening.

The model worked well, particularly steering and the drive.  However the extraction and the hopper opening was a little less reliable.  The hopper was too heavy for a single mini linear actuator, and the compaction device was not stiff enough.  It happened to get caught on some of the internal edges on the inside of the hopper.  The next garbage truck will need to be built a little more sturdy.

The full gallery may be seen here.

Kenworth T55


Traction.  It’s all about traction when designing a trial truck.  Because of this, many builders have tried a number of different solutions in designing their own trucks: differentials, gearboxes, various numbers of wheels, various gears ratios, countless suspension designs, and on and on.  So why would it be any different for my trucks?  Every truck I make is a reaction to some set of problems I have encountered with a previous truck.  This is my current solution.

The full gallery is here. Instructions are here.

The Kenworth T55 started as a proof of concept, and turned into a design of a fictional truck.  I wanted to somehow see if there was a way to use differentials in a successful trial truck.  For this to work, two things had to be accomplished.  First, there had to be a way to keep the tires from spinning uncontrollably when they lost contact with the ground.  And second, the torque going through the differential had to be low enough that it would not shred the gears inside the differential when the truck encountered an obstacle.   Could I make axles that had a limited slip differential while having all of the gear reduction at the hub?

Enter turntables.  I have seen some ideas before, most sigificantly from Borec, including this truck, so I went to work.  I designed a mount for the wheels and tires, and placed the universal joint as close the wheels as I could.  Then I used a limited slip differentail design, and sent the driveshaft back to the body.  A simple steering design was used, and the two fuctions passed through the common design of using a differental body through a turntable.

The chassis was designed to keep the weight low, both is mass and location.  As is common, I used the Power Functions XL motor for drive, and I decided to use the 8878 Battery box as it was significally lighter than the other design.  In addition, I would have a drive shaft and a steering shaft running the length of the truck, so the motor and power pack needed to set on both sided of the truck.  Also, because I used the turntables, the drive shaft was very high.  This gave great ground clearance, but I needed to keep the heavy components low.  By having both large components on the side, I was able to keep a short wheelbase of 30 studs, and keep the mass centered and low.  The driveline was complete.

Ever since my GMC 2500, I have held to the belief that a linked suspension is the most efective setup for four wheel trial trucks.  The design keeps all four wheels firmly planned, and does not have the wobbling feel of many pendular suspension designs.  But as is often the case, I ran out of room to place a link rod between the two wheels so I opted with useing the rubber connectors to keep the axles level.    I added a body, and a steering motor, wired everything together, and I was done.

So how did it work.  As you can see in the video, the suspension was effected by the steering and drive shafts.  This further confirms my thoughts on the linked suspension.  Second, the turntables did not really add much.  They added a lot of friction to the driveline, and though they kept the differentials safe because of the tall final gear they did not really isolate the forces on the differential as much as I would have liked.  Third, the limited slip differentials worked well, but still allowed for too much wheel slip.  I ended up replacing the rear with a locked axle, which seemed to work well.  So, for the next truck, bring back the linked suspension, and find a better differential solution.  Maybe then I can find some more traction.

4×4 8081


Truthfully, I was excited about set 8081 when it was first announced.  I liked the size.  I liked the coloring. I liked the stance.  But mostly I liked the potential.  Most of the Technic community dismissed the 8081 because of its watered down functions, but I was interested in making some changes to see if I could make the Cruiser Extreme.

The full gallery can be found here, and instructions here.

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I first added a V-8.  There was plenty of room, and after seeing a great modification from Efferman, I had some ideas.  It was a simple addition.

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Next was the drivetrain.  This was a little more complicated.  I wanted to make it four wheel drive, and I wanted to make sure there were three differentials.  I rebuilt the rear axle, so It would have a more active setup.  I put in longer shocks, and added a Panhard rod, and two stabilizing links.  It worked well.  The front axle was more challenging.  The new CV joints made the project a little easier.  Once I had the differential place, I had to fit everything around it.  The steering rack was placed upside down, and was connected directly to the existing steering link in the original 8081.  Then I added a Panhard rod on the front of the axle, and rebuild the front bumper, and everything was set.

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Instructions can be found at Rebrickable.com or here.

Full gallery is here.

I also created a motorized version after a number of requests.  You may see the gallery for that MOD here.

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