doug72

Perhaps 16 x 32 L baseplate could be used to mount two miniloops linked together or a 32 x 32L baseplate for four mini loops linked together.

Thanks - the tracked version is much easier to drive & steer than the wheeled version of my MOC. Turning on the spot problem: Seems the weight of the rotating structure is causing the tracks to bow inwards slightly and tracks start to rub on the under carriage side frame. Have to find away to prevent this. Update: Now fitted more bracing to prevent the top of track units bowing inwards due to weight plus steering now uses an L motor. Battery box mountings modified so no longer have to remove both track units it to fit new batteries. Return track rollers changed from 24 mm dia. wedge wheels to 18 x 7 narrow rims as track tension too high causing cogging.

Thanks for your design, your compact version is just what I am looking for to reduce overall length of the subtractor unit to fit into my Crawler Under Carriage MOC giving more room to fit a large battery box out of view.

 I have made a stud-less version and eliminated the chain by using an offset 12T double bevel gear meshing with the two 16T gears.
Tested using two M motors and performs OK. Should be able to use XL/L motor combination OK as well. 


Material Handler now mounted onto the crawler under carriage, it was not a direct exchange as I had hoped for. Had to add an extra 5 x 7 frame and adjust slightly the connections to slewing ring. Tested and performs OK on a hard surface with sharp turns possible while in motion forwards or backwards but reluctant to turn on the spot. 
 Probably due increased weight, a run down battery and an M motor for steering not powerful enough, L motor to substitute. I will return Material handler back onto the wheeled under carriage and use the crawler under carriage for another MOC I have in mind. Side View: 
 End View: 
 Oblique View: 
 Video:

Looks good, slewing using the Z60 turntable gear ring instead of the gear quadrant gears should be a lot smoother. What does the co-axial XL motor drive ? Doug

Thanks @jotta93 @Aventador2004 @Sjoemie himself @ColletArrow Raised track version it is - both now changed and functions well. Still looking to see if can locate the battery box better or use an AAA batterey in its place. The two trans-orange 1 x 2 tiles act as IR collectors !!!

This is the subtractor unit I am using for my latest MOC. XL motor for drive and M motor with 2 stage reduction for steering.

Update: 
With the existing under carriage I found I was unable to install a battery box AND a PF receiver, this due to extra space used by L motors and the double gear reductions in the subtractor unit, so had to completely rebuild the unit, using XL & M motors with single stage gearing. Only way to install the battery box was to install it upright to allow Pf Rx to go behind it with enough space for cable connections.
 However the battery switch and cable plug now fouled the underside of the turntable rotating base frame so had to raise the turntable mounting 5 x 7 frame by 1L to get clearance. Ground clearance below battery box & XL motor only 1L. Side track units: 
Getting the track tension just right has proved awkward do the due to track link wear after many others usage on MOCs. I had to carefully match track links to take account of this wear.

 Now devised two versions: track return flat and track raised return as per real machine.
 Both use 16mm wedge wheels for track support. Which looks better ? Flat track return: 
 Raised track return: 
 Subtractor unit revised and now uses XL motor for drive and M motor for steering. 
Tested and OK on carpet with turn on the spot and full range of turns. Topside showing battery box and PF receiver: Next mount existing rotating unit from the wheeled mobile material handler.

Thanks for comments & observation. I used two L motors as with the multiple pin holes make it easy to build into the undercarriage structure. Used gearing to get desired speeds for travel & steering. Tested yesterday usings PF speed controller and OK when moving forward and backward and able to do steer between large to small radius turns. However it refuses to turn on the spot other than on a very smooth surface when it is very jerky. This is due to the white 24T clutch gear between L motor and the 16/24T Differential slipping intermittantly. I used this as a normal 24T gear rubs against the side frame where as the white 24T gear doesn't as it appears to have slightly smaller o.d. So I have to change the gearing and might see if M motor strong enough to turn on the spot and use that if it does. An XL motor to large to replace the L motor without it touching the ground. Re Track unit - I have space to raise the track return run by 1L and make it look more like the actual machine and will also improve track tension. Odd Problem: I always seem to be short of 1 piece when trying to build to a uniform colour scheme when building MOCs and have to substitute another colour !!!! e.g, I only have 3 dark tan # 1 connectors when I require 4 etc. !!

Now fitted six rollers (without tires) for track return and is much flatter with only slight sag. 
Rollers with tires are better but I don’t have enough for both sides.
 Tested and looks OK when in motion.
 Next step add battery box & PF Receiver. View with covers removed: 
 View with side covers. 
 Now tried without any return rollers and beam substituted for the track to slide along which performs OK without any sag. View without return rollers and side covers in place: Clearance between track & underside of rotating structure is 2L.

Yes found it on YouTube. It's a very fast earth mover. May rebuild the first ever Lego Technic 8275 set i got for Xmas some years ago, which got me into Technic builds and adapt it with the power dozor blade, will make a nice challange to get it working. Thanks for the comments: Just tried using small sprockets with 8 small track support wheels and 2 larger return wheels - result a very jerky track. I will revert to the large sprockets and try some form of sprung return rollers, trying not to let the top run of the track get too high so it doesn't foul the rotating structure. Could try tires on the return wheels to take up some slack. If at first you don't succeed try try again !

A magnificent masterpiece.

Update:- At the moment I am building a crawler under carriage upon which the existing rotating structure from the wheeled version can be mounted. 
 It is based on this design as used on the real machine. Turntable unit will connect to the 5 x 7 frame with the 8 blue pins.
 No changes are required to rotating structure.
 This could also be used for any future crane MOCs.

 Actual crawler side track unit: 
 So far have sorted out the drive to the tracks which uses two L motors and a subtractor unit.
 Track speed is a too slow so gearing changes are required. 
Had thoughts of a 2 speed solution but space tight so it will be single speed only. 
Yellow sprockets to change to black & I may the use the smaller size sprockets along with ten small track wheels. 

My biggest struggle is getting the track units to look OK like the real machine without too much slack in the tracks - its something I always have trouble getting right.
 Have tried a track tensioner but makes the track units too wide. Suggests & comments welcome. I have made two versions of the track units - see photos.
 Both use five track support wheels plus two return wheels.
 The real machine uses ten smaller support wheels & I will also try a version to see how it performs.
 Under carriage will have its own battery & PF Rx. Underside view: 
 Overhead view: 
 Track unit without side covers: 
 Track unit with side covers:

Thanks for the comments, I was pleased that when build was completed that the drive and steering worked with all the added weight etc. Here's a video of an unusual machine & possible MOC with three caterpillar tracks !!

And claw grab is able to pick up small round cans that contained beverage !!!

To remove stickers use a the edge of a sharp blade to lift a sticker corner enough to grip with fingers then s l o w l y ease it free. Go to fast will break them. Warming them slightly helps. I have transferred some several times this way.

Thanks Andy glad you enjoyed the video, Took me awhile to shoot in segments and then editing it together The clam shell grab picks up more than the four claw (orange peel) grab which looks more impressive. Might try and make a demolition shear attachment if I can find parts to replicate the scissors arms. Next step is a crawler under carriage that existing upper rotating parts could be mounted on and make it also usable for another possible MOC of Dead weight pile driving machine. I have a spare 13L turntable for this. Another possible MOC is a bulldozer which has three (3) caterpillar tracks ! YouTube is a great source for unusual machines. Doug

Many thanks for your comments which much appreciated. My wife also likes it as it no longer resides on the dining room table !!! Its been a long haul but its not over yet, some improvements still possible. While making the video and when it crashed into my camera I only just managed to save it from falling off the table !! Result the main boom became detached from the hinge connectors and dipper arm also partly came apart. This highlighted a problem with the Main boom connection between hinge & taper panels which only had 4 pins connecting them. 
 Solved by modifying as shown on photo by installing a brace so cannot pull apart. Dipper arm - I had forgotten to add link braces between the 3 x 11 panels. Now fixed 
using 5L thin beams with 3/4 pins. Now starting work on a tracked under carriage which will use a subtractor system for drive & steering that can be subsituted for this MOC or used for another potential MOC. Doug

Dipper arm actuator: A problem arose as the dipper arm is near fully raised. which caused linear actuator ram to sag where the extension push rods connect to the L.A. end,. 
Solved by placing two taper guides to keep ram in place without sag. MOC now completed :

 Final Video:- Make sure to watch to the end to see the collision with the camera when I nearly drove it off the table !!!

Those cleat wheels with all the pin holes in the hub might be useful to make a planetary reduction gear unit.

Thanks, while forum off line gave me time to sort it out -and avoid the snow !! Tested with orange peel grab and able to grip, lift and hold a small aerosol can.

Elevating cabin: as friction pins not enough to keep cabin in the raised position I used a small linear actuator but the lift range was too small. Tried a large l.a. operated by hand, and the lift range was OK, so now power operated by M motor direct coupled to a linear actuator & controlled by PF switch.

Jotta - no problem if you want any close shots let me know. I might have a go at a demolition attachment. I have just completed the build on the mobile under carriage. Mark 2 Boom & Dipper Arm successfully replaced the Mk 1 version and looks and functions much improved. All functions tested without any problems, slewing is very smooth, weight distribution OK and no additional counter weights required. Controls: Three PF receivers. Rx 1: Undercarrige drive and steering using basic controller Rx 2: Slewing & Main boom using basic controller Rx3: Dipper arm raise / lower & drive to grab attachment using speed controller. A new video in next few days. Next step is to build an alternative tracked under carriage. This has been my most succesful MOC - at times frustrating & challanging but an enjoyable build.

Mark 2 Main Boom & Dipper arm Completed using flat panels, tested and performs better than I had hoped. 
Dipper arm swing range is now from vertical to 30 degs. above horizontal when main boom fully raised. 
 Drive to grab attachments now has a linear clutch to protect U-joints and the mounting of inter changable grabs simplified. Found best to control dipper movements using a speed controller with PF switch for the main Boom. Will be making a new video soon. Dipper arm in lowered position: Dipper arm fully raised:

Thanks for your comments. Do you reckon you've learned anything new from this build? Yes be a tidy builder !! I tend to discard unused parts into a heap then slide them into a container before having periodic spells of sorting & putting parts back into their correct storage drawers etc. As I design and build without instructions its best to build in stages, test, review & modify until satisfied. The initial idea for this MOC stemmed from a workable but simple out rigger system & suitable size tires. I also tend to make sub structures to try out placement of parts and gearing etc before incorporating into the build. In the case of the Mk2 boom I have used a full size test rig rather that try to work directly on the exisitng build and once satisfied install it. Its much easier to make changes that way. Also try to anticipate what parts required and order any I don't have. Had to rob previous MOCs to build this. At the moment I am short of one 3 x 10 yellow panel for new dipper arm so will have to remove one from the body work and subsitute with three 11L beams in its place. Once new dipper arm made will post a video of the test rig in action. Doug