doug72

A very interesting and unusual model, lots of functions. The out rigger system might just be what I am looking for my current MOC. Doug

A truly amazing build and the the on board camera video stomach churning ! Worthy of HOF.

Steering issues fixed at last ! Seems I made an error previously with drive train differentials in the wrong place, with them placed between fore and aft caster units on each side of under carriage. This caused a problem when Mode 3 steering required. i.e Radial steering as wheels on the outer radius could not run faster than those on the inner radius causing gears etc. to grind and skip. Now revised as per schematic layout shown: L motor drives central differential with outputs to the left hand and right hand sides of the under carriage. 
Right angle gear box drives the wheels to each caster unit. Each caster unit still has a differential. Tested and functions well in all steering modes, and can perform tight turns without gears grinding or skipping now. Managed to re-configure without a major strip down and the steering system remains unchanged. Battery box now installed centrally under the turntable gear ring. Next step: install four riggers.

I have seen working conveyors on model railways (OO / HO scale) that used de - inked type writerr ribbons effectively. Maybe a similar material but wider would work. To kept belts on the end rollers they should be crowned. i.e. diameter in centre of roller should slightly larger than the end diameters.

As you rightly pointed out when radial turning, the wheels on the larger outer radius have further to travel and hence have to run faster. I think I have been ambitious in trying to have all powered / steered caster units. With my current set up this does not seem achievable. Going to try powering only one pair of casters at one end of under carriage with a single differential between sides, this along withe the differentials in the caster units should ensure all wheels rotate at correct speeds. Just done a quick trial by disconnecting the drive to one pair caster units with a tempoaray lock on the redundent drive axles. A big improvement and should be even better once I add a central diff. Drive will be "U" shape with the L motor driving the diif. - then splitting to left & right powered caster units. The other pair at other end of under carriage will run freely with thier own diffs. to allow for turns. All caster will still to be steered by two motors. One other possibity is two independent drive systems for each pair of casters but controlled by one PF channel. Will be re-configuring and testing tomorrow.

Thanks for your input.
 Unfortunately its too large to fit in space available. I tried three differentials before in drive train on my Mobile Ship Loader Conveyor but it failed.
 See topic on page 2
 
If any wheel loses contact with the ground it starts spinning at full speed and ALL other wheels stop turning. The under carriage is quite rigid, no easy way to give them independent suspension. IMG_5112 by Doug Ridgway, on Flickr Probably ony workable solution would be MIndstorms EV3 with each caster unit powered and steered individually. As it is now I am happy with steering for modes 1 & 2 and mode 3 if limit the degree of turn.

Thanks for the tip, now tried and easy to find out which motor is slower.

Sorry missed your post. Thanks for the instructions. Will study & test again. Doug

Drive for steering and wheels revised: It took quite a while to get all eight wheels rotating in the same direction !!! Underside view Differentials are now used for drive to caster wheels. All motors for steering and drive grouped together, but this leaves little space for a large battery box . May shift steering motors or battery top side.
 Two Steering motors now installed top side as per an earlier image. Large battery box now installed inside under carriage. Out riggers will probably be operated by HOG or PF switches. Note: Caster wheels are correctly aligned, image distorted by camera. Top side view Turntable gear ring installed.which is supported at 8 locations.
 Had to raise this by 1L to clear differential Z28 gear to prevent slewing gear fouling it. Rotating base for crane structure: Four sets of double wedge wheels are used for support, 12T slewing gear in position which will be driven by an M motor. I have since found that Liebheer make a rail mounted version of this crane which is mounted on a portal structure, much eaiser to build as no steering would be required.

A subtractor unit allows one motor to drive tracked vehicles in a straight line. When second motor is used in conjunction with first motor it speeds up one track and slows down the other track to allow large radius turns Second motor used on its own will run tracks in opposite directions so vehicle can turn on the spot. Sariels guide book explains.

Thanks, I look forward to reading your review. Mine is a hand me down from grandson who got a Technic which contained it, can,t recall set number, but it had Control centre in it, which I also have. Took me long enough to figure how to open the battery compartment to replace the battery ! Doug.!

Thanks - had a look but like you found it hard to figure how it works, think it would be too large to use anyway. I have devised a c/o unit to dis-engage and lock the output but its to large in fit into the drive train !! See image, it might be usefull for to someone. One drawback is the slackness in driving ring clutches - almost1/4 turn slack in the output. I have re-tested a two motor solution but with each motor on seperate PF channels. Seems to work better. For Modes 1 only one channel operated. For Mode 2 steering both channels used with small c/o switches on basic controller in the same position and all caster units turn in same direction. For Mode 3 steering one switch has to be change to other position and when both levers moved together each pair of caster unit rotate in opposite directions to each other. To re-align pairs of caster if get out of step then each caster pair is turned individually. Next step is to re-build the under carriage to allow two differentials to be installed in the drive train to wheels.

I have one of these and have been testing the speed of all my PF motors especially M motors I am using for my latest MOC to try and match a pair of steering motors. Does anyone know where I can find instructions how to use it as I am getting all sorts of weird RPM readings way above Lego stated RPM.

If do that then OK to steer in a curve but not in straight, crab or sidways. Diff required as when caster unit turns on the spot wheels rotate in opposite directions. For my mobile ship loader coveyor MOC I did have diffs in the drive system and there is space to fit them where the the drive splits fore & aft each side. When I used two M motors for steering both were control from one PF channel and due to slight differences in RPM for each M motor that caused the out of sync problem May revert to that, but use separate cPF channels to control them. First I an going to test a clutch unit that will dis-engage one pair of caster units and lock to prevent turning and allow steering from one end only.

For a six fold purchase to raise and lower a heavy bucket chain excavator boom I used these. They have a deeper groove than wedge wheels and keeps the cord in place better. They come in two versions:- LEGO Rim Narrow Ø18 x 7 and Pin Hole with Shallow Spokes (56902) LEGO Rim, Narrow Ø30 x 14 with Axle Hole (56904)

This is the drive path for steering (Green line) and drive to wheels (Red line) L = drive motor / M = steering motor. As it stands will only be able to steer the undercariage in straight - crab - sideways directions. Looking for a way to disconnect aand lock a pair of caster units at either end so other pair of casters can turn independently for steering The change over clutches have too much backlash, possible sliding gears mind work. Anyone got ideas how this can be achieved ?

There is no slippage in the drive to steering for each unit, the slippage is between the two units due to un-eqaual motor revolutions. Now tested a one motor set up with all units hard coupled together, just need to sort out best location for the Steering motor. Its hard to see in the images due to balck beams & gears. ( using up my over stocked of black parts ). The drive for wheels runs down each side of the undercarriage and is cross link on the centre line from the L motor. Steering drive is across the ends of the under carriage and cross linked on the centre line, had to dog leg the cross link axles so one passes below the other. Smaller tires now fitted and looks much better. Will try and re-design the caster units to a 4 wheel bogie verision.

Thanks, I have been thinking about fitting smaller wheels, current size is 49.5 x 20, but can fit 43.2 x 22ZR tires on the same hubs. I will also see if it is possible to have 4 wheel caster unit bogies. Update:
 Drive now installed and initially used a worm drive giving an overall reduction of 12:1 using 20:1 worm gear and & 20:12 step up gears which proved too slow. Now changed to direct drive via 12/20 reductiongears. Under carriage unit tested for drive and steering functions. Steering: a new problem has appeared not identified in previous tests !! Currently using two M motors to turn each pair of caster units.
 The problem is the speed of each motor is sightly different causing units 1 & 2 to get out of sync. with units 3 & 4 especially if a lot of turns are performed !!! So I may revert to a single motor for steering but dispense with trying to get mode 3 radial steering. I.e. just have mode 2 for straight, crab & sideways motion with maybe a way to lock the caster units at each end for mode 1 steering. Probably means reconfiguring the drive and steering shaft / gear paths.. Unless anyone has a fix for this problem. PS I think this may have also been an unidentified problem with the Mobile Ship Loader Conveyor. Top side view. Underside view.

Both steering motors now installed along with two PF switches. Tested and functions OK for all three steering modes. To keep in sync. you need to return all caster units to the fore & aft position, before changing to next desired steering mode. Mode 1: Could get away with one PF switch but with two it allows for either end of the under carriage to steer. Mode 2: Performs well at all positions of caster unit and can change direction on the move from fore & aft to crab to sideways.. Mode 3; Performs OK as long as do not try too tight a turn, should be better once drive is connected and iall wheels are powered. Next step is to installed the wheel drive to each caster unit, may need some adjustment of the differentials to ensure alll wheels run the same way. Under carriage is 23L wide x 37L long.

My next MOC is a freelance version based on a Liebherr 120 Crane but will only have four caster steering units instead of six. Following the build of my mobile ship loading conveyor, a number of problems arose and were solved & almost all due mainly with the various steering modes. 

For my new MOC initial thoughts were to have a mechanical solution to control the steering using only one M motor and a selector gear box (see image) Black = M motor input. Red = output to caster units 1 & 2 with direct drive from M motor. Yellow = output to caster units 3 & 4 via selector gear which can either turn units in same direction as 1 & 2 or in opposite direction, plus stop the units turning. Result: selector unit too large and complicated and suffers from the excessive backlash due to the red gear clutches, about 90 deg. lag when reversing drive to units 3 & 4 resulting in caster units out of step. REJECTED. For the the previous build I used the small c/o switches on the PF controllers to set the steering modes but found this to be confusing to get right.
 Reverting to a two motor solution for steering as per Mobile ship loading conveyor, except I will use PF switches this time to select the required mode for each M motor. 

 This will allow for 3 steering modes:
 1/. Normal steering using only 2 caster units with other set in straight position. 2/. All caster units turn together same way for straight, crab & sideways movements. 3/. Pairs of caster units turn in opposite directions to give radius steering. 
A 4th function is possible if used an M motor for each uint plus four PF switches.
I but don’t plan to install this due space constraints. The build so far: " MOC will have these functions:- 1/. Drive travel - XL or L motor. 2/. Steering - two M motors. 3/. Drive outriggers - ( may be HOG ), depends on space in the under carriage. M motor with PF switch. 4/. Slewing of crane - M motor 5/. Luffing of jib - L motor. 6/. Hoisting - M motor. PF receiver and battery in the undercarriage & the two PF Rx & battery in the rotating structure.

A mechanical solution built to control the caster units BUT takes up too much space and over complicated. Also has a BIG drawback with the lost motion in the red clutch gears amounting to 90 degs. when rotation is reversed. This means the pairs of steering units will not always stay in sync. So back to the drawing board. I have made a mock up test rig using two M motors and two PF switches to control the steering modes. Output from a PF receiver goes to both PF switches which in turn control each motor, allowing selection of CW - stop - ACW. By this means the desired steering modes can be achieved. With 4 motors plus 4 PF switches rotation on the spot should be possible. NOTE: Closing down this thread and will be starting a new topic soon for my next MOC which will be a freelance MOC of an RTMDC ????

Update: Completed the build and functioned as I intended apart from the caster steering which proved quite difficult to control & synchronise the two steering M motors to achieve the various steering modes. Now disassembled apart from the four caster steering units which will be used again for my next MOC. A new topic will be started once I decide on what to build. Currently developing a steering system for the four caster units that will use only only M motor and via a changeover gear box will be able to perform the various steering modes (1, 2 3 ) except for rotating on the spot. Steering options.
 Mode 1: Two casters units only steered with other pair fixed i.e. normal steering Mode 2: All four caster units rotate the same way to provide driving straight / crab / sideways. Mode 3: Pairs of caster units steer in opposite directions to give radial steering. Mode 4: will not to be fitted
. This would require each caster unit to turn towards a theoretical centre rotation point and would require a very complex gear selector box to achieve this or use four EV3 medium servo motors & use Mindstorms programmed to control them - probably lack of lack of space to do this unless the MOC is very large.!!

The heavy duty differentials I developed for my Boydell Stommper TC12 entry using a Z60 turntable and knob gears could be a solution. I used an L motor but an XL motor would also be OK. Various gear ratios are possible to drive the turntable either by spur gears or for a high ratio by worm gears. You could have two per track i.e. one at each end.

Definitely seems to be due to friction & / or binding of parts causing this problem. The front & rear wheels are rotaing at different speeds due to the red 24/16T differential spitting the drive power. i.e. twin rear axles have more resistance than front axles. It pays to test things as the build progresses rather than complete the build before testing, that way you have an easier fix if any problems saving a big strip down to find the fault. Try following tests and run motor for each test. 1/. Front wheels on the ground, rear wheels in air. 2/. Front wheels in air rear on the ground. 3/. Repeat 2/. but have one pair of wheels on ground, the other pair in air. 4/. Repeat 3/ but reverse which wheels on ground / in air. 5/. All left side wheels on ground, right side wheels in air. 6/. As 5/. but left in air, right on ground. Should then be able to determine which parts are binding. Good luck !

A neat & simple idea !