[MOC] Robot Arm – Liebherr 42100 Alternative Build – Uses 7 Powered Up Motors

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Robot Arm – Liebherr 42100 Alternative Build – Uses 7 Powered Up Motors


I have been wanting to build a 6-axis robot arm using some of the instructions available that use 2 EV3 kits.  But I wasn’t prepared to buy a second kit just for this reason.  When I saw that the Liebherr came with 7 Motors, I was inspired to purchase it so that I had plenty of Powered Up Motors I could use in the future.  And I soon realised it should be possible to build a 6-axis robot arm with what was available, although I would be limited with only having one large turntable.

I started building from the grabber, as I realised that would require the most specialised parts.  Once I got to the first arm I realised that this would be the most flexible with what parts could be used, so I then worked on the upper and lower base, followed by the first arm, then I finished with the tracks on the panels and decorative items.  I was initially going to build it with caterpillar tracks similar to the Liebherr, but realised it would have more of a factory look if it rolled on straight tracks on a floor.

Most sections were built by firstly focussing on the functionality required, then building the frame around this, reinforcing critical areas, and further reinforcing these to make them strong enough.  Most sections had a complete rebuild when it was realised that something critical had to change to get it working properly.

The project took 9 days to complete, working on it about 2-4 hours each day.  This is the first MOC I’ve completed, and I’d credit this to having a limited number of parts to work with, as well as a focus on mechanical features rather than aesthetics.  The modular nature of the project also helped as there were clearly defined global requirements for each smaller section.

I don’t intend to produce instructions or an electronic model of this as I feel it is a substandard build, partly because of the limitations of parts, and partly because I haven’t the expertise, time and patience to improve the quality.  Many sections felt like they were just hacked together to make them work with what was available, and there would be better construction techniques that would make things work better.  During construction there was some bending of liftarms and axels as well as extremely delicate operations required to place some of the parts.  Other limitations of the model are described in the Limitations / Possible Improvements section below.

I’d encourage anybody interested to have a go at building a similar model, I would be delighted if someone could make a more professional version and even produce instructions.


A: Tracks and Floor. Made with Link Tread connected to array of panels.  Some decorations added.
B: Lower Base. Drives along tracks using Motor 1 and extra-large sprocket wheels.
C: Upper Base. Rotates (unlimited) on lower base using Motor 2 and curved gear racks, with small turntable in centre.
D: First Arm. Moves up and down with Motor 3 and 2 large linear actuators.
E: Forearm. Moves up and down with Motor 4 and 2 small turntables.
F: Wrist. Rotates using Motor 5 and large turntable.  Limited rotation because of cable going through centre of turntable.
G: Hand. Moves up and down using Motor 6 and 36-tooth gears.
H: Grabber. Opens and closes using Motor 7 and a range of parts including several 16 tooth gears.




Powered Up Motor Size

Powered Up Battery Box


Base moving along tracks using extra large sprocket wheels




Upper base rotating on lower base, with a 28-tooth gear rotating against the curved gear racks, and a small turntable at the centre.




First arm moving up and down, using 2 large linear actuators.




Forearm moving up and down, using 2 small turntables.  The gearing down is done independently for each turntable to spread out the load. 




Rotation of the wrist using a large turntable.  The wires for motors 6 and 7 goes through the centre of the turntable.




Movement of the hand, using 2 36-tooth gears connected to liftarms.




Opening and closing of the grabber.  The movement from the motor comes through a toggle joint in movement 6.






Advantages of using the 42100 Liebherr set

Having limited parts to consider reduced building time.

Set has 7 Powered Up Motors with 2 Battery Boxes so control was easy using BrickController 2 and Bluetooth Phones.

By laying out the

Colours were main White, Dark Bluish Grey, Light Bluish Grey and Black, so there were no clashing colour combinations.

Limitations / Possible Improvements

Only 1 large and 4 small turntables available.  Ideally 2 large turntables would be used for moving the first arm (D) and the forearm (E), and 1 large turntable would be used at the centre of the base.

Having a small turntable at the centre of the base meant that the lead from a motor couldn’t go through the middle, which prevented a motor being put in the lower base, as it wouldn’t be able to be connected to the battery box.  For this reason, motor 1 was put in the upper base, and an axle went through the middle of the small turntable to transfer movement to the extra-large sprocket wheels.

Only 2 8-tooth gears available, limiting gearing down to using mostly 12 and 36-tooth gears.

Parts in limited supply, and many useful technic parts not available.  Gears and axles especially had to be rationed, and careful consideration was required for where to use many parts. 

The grabber was primitive because of limited variety of parts.

Possible Improvements

Redesign the grabber, possibly using a small linear actuator.  This should also improve the strength of the grip, which is currently quite weak.  The grabber currently uses both 8-tooth gears, which could be put to good use elsewhere in the model.  It would be nice not to have the grabber open or close when the hand (Motor 6) moves.

Balance the forearm more by repositioning Motor 4 and Battery Box 2, so that movement 4 requires less force.

Speed up the linear actuators so that the First Arm (D) moves faster.  They were already sped up compared to the first arm movement in the Liebherr set, but could probably have the speed increased further.

Reposition the linear actuators so that there is more movement of the First Arm (D).

Redesign the Upper Base (C) so that Motor 2 does not stick out of the side.  Motor 3 and possibly Battery Box #2 could be put in the First Arm (D) where there is more room available, although this would mean the linear actuators need to be upside down as they would be driven from above.

Make it so that the model doesn’t move so roughly on the tracks.  Adding some of the 20-tooth gears with pin holes at ground level may help this.

Overhaul each section to use better construction techniques.

Add more decorative parts, especially around the tracks.  Many studded pieces were left over which could be used creatively.  It would be nice to use the Liebherr bucket somewhere in the model, possibly upside-down at the front of the base?

Photos of detail







Leftover Parts:



Controlling with Brickcontroller2:



Original plans.  My son added the light blue to reflect the changes I made.







Edited by AllAboutTheBricks
Add youtube video now that I have a link for it

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This is the sort of thing that TLG should provide as B-models for the large C+ sets. Something completely different from the A-model, but still very cool and interesting on its own right. Well done!

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Interesting. Thanks for your sharing. Good job.

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