[MOC] RC-Pneumatic Backhoe

[2GodBDGlory]

It seems that one of the most recurring things we see in wishlists on here is an RC Pneumatic backhoe, and the sheer complexity of backhoes has made them attractive to me for a while. It wasn't until @J159753 happened to suggest backhoes to me that I started thinking about the concept seriously, and got quite inspired!

The model has ten separate RC channels, with five mechanical RC functions and nine separate RC pneumatic functions, so, as you would expect, some creative thinking was required to get this many pneumatic controls run off of only a few motors!

First I'll discuss the pneumatic function-shifting module, since that's probably the most interesting, and then I'll get into the main presentation:

So, for the function selection, I settled on this mechanism using three PU L-motors for smooth programmable control from a PU train remote via a custom PyBricks program. One motor ran the 6L worm screws here (Mine are black 3D-printed ones, because I haven't gotten my hands on original Lego ones yet). It then moves an assembly through four possible positions. Then, in each of those positions, two sliding worm gears can be activated to rotate a sliding fork to engage a valve, in a way similar to @Mr Jos's concept shared earlier, though my design does have a lot of major differences from his.

Spoiler

 

The programming for this was rather challenging for me, but in the end it works fairly well, and is able to move extra-far to compensate for the backlash in the system. The system ended up being relatively compact, in my opinion, though still quite large. It's reliability was fairly decent, though sometimes the sliding parts would catch, and some more complicated tuning in the code could have improved it further. I'm quite happy with the concept, though!

Also, it's worth noting that this only provides eight of the nine RC pneumatic functions in here; one is run separately off a traditional valve

 

Functions:

• Pendular front suspension
• Pantograph windshield wiper
• Opening doors
• 4WD (PF L)
• 4WS (2x PF Servo w Switch)
• Auxiliary Compressor (PF M)
• Arm Traverse (PF M)
• Differential locks (PF M for valve; 2x small cylinders)
• Arm extension, "Extendahoe," (PF M)
• Pneumatic function selection (3X PU L)
• 4-speed Gearbox (PU L)
• Front Arm lift (2x large cylinders)
• Front bucket (2x long/skinny cylinders)
• Outriggers (2x medium cylinders)
• Arm rotation (2x medium cylinders)
• Arm lift (1x large cylinder)
• Arm articulation (1x large cylinder)
• Bucket motion (1x large cylinder)
• "Thumb" (1x medium cylinder)

Aesthetics:

The bodywork is quite simple, but I think it's refined-looking enough for my standards. I used the JCB 4CX as a rough template for the model, but didn't follow it too closely (For example, my wheelbase was forced to be considerably longer) I was also super happy to be able to route ten pneumatic hoses to the rear by hiding them inside the 5L liftarms in the rear mudguards! It was cool to be able to use the exact same tubes to support the mudguard and run the pneumatics.

 

Pendular Suspension:

Nothing fancy here, but my outline requires a heading for it

Pantograph Windshield Wiper:

Spoiler

This is probably the best picture I have of the most satisfying function on the model! It was kind of an afterthought, but it ended up working really nicely to move the wiper side-to-side on a 4-bar linkage made of some bar elements connected to Robot Claws via super short pieces of pneumatic hose. It was connected to a lever on the rear of the roof by an axle for easy control, and was very fun! See the video below to see how it works.

Opening Doors:

Spoiler

I made sure the doors could open 180 degrees to allow the operator to leave them open for fresh air in the summer!

4WD:

The drive was done by a single PF L motor, and worked quite nicely!

Four-Wheel Steering:

When I saw that the JCB 4CX had 4WS in real-life, I knew I wanted to try doing it myself, for that extra bit of gratuitous complexity I enjoy adding! I used one PF Servo on each axle, and coupled them with a PF switch on the driver's right side, to allow for switching between 4WS, 2WS, and crab steering. Sadly, the rear Servo started malfunctioning during the build, and would only turn one direction in the end. It's probably fixable, but I didn't care to take apart the model to deal with it.

Aux Compressor:

So, knowing that space would be limited, and that huge quantities of air would be required, I made it my plan to primarily run the model off of compressed air stored in an external 2L bottle, filled with a bike pump. This worked quite nicely, simply attaching to a port on the side of the backhoe, and requiring a couple manual valves to be flipped to connect it to the system. However, I didn't want that to be my only source of air, since I wanted it to be capable of truly disconnected RC operation, so I included a basic single compressor system running ungeared from a PF M motor. It's not fast, but it does its job of allowing for true RC functioning.

Spoiler

The main air supply

Compressor

Arm Traverse:

One goal with this model was to allow the arm to slide left and right, like a real one. Pneumatics seemed like a poor fit for this, so I chose to run it off of a couple more 3D printed copies of Lego's 6L worm screw. These parts worked quite nicely for it, but bracing the whole arm on a sliding assembly proved very challenging, and once I added all the pneumatic hoses required to run to the arm, the traverse's operation became rather unreliable and often needed help.

Spoiler

Differential Locks:

With the Yamaha's new 2L driving rings compatible with the new system, we can finally get a modern diff+lock into a nice, odd, 5-stud space, so I was happy to be able to make that fit here! I used a PF M-motor with a basic mechanism to run a ninth valve for this function, which just used one small cylinder per axle for two diff locks.

Spoiler

Arm Extension:

After seeing the "Extendahoe" feature on some real-world Case backhoes, I figured it should be part of any ultimate backhoe MOC I built, so I included it here, using a PF M motor running a framed rack via a worm gear with a safety clutch.

Spoiler

Pneumatic Function Selection:

(See above, just after the introduction section)

4-speed Gearbox:

I always like putting supercar-style functions into other types of machinery, so I was happy to include a compact little 4-speed gearbox in this model! It's able to be very small thanks to both the 2L Yamaha driving rings and the way I was able to integrate it into the rear axle. Instead of using an extra set or two of gears to change the gear ratio between the two driving ring's shafts, I appropriated the 28T gear that was driving the differential, and then added two 8T gears to it, to get a 8:28 gear ratio between the shafts, and then 1:1 and 12:20 ratios between the two ends of the driving rings. It was super compact, and actually held up well enough in practice, despite the questionable 8T-8T gearing. One downside was that the natural shift order would be something like 1-3-2-4, but because I was shifting it with a PU L-motor, I was able to program it to shift in the proper order anyways.

Spoiler

Miscellaneous Pneumatic Functionality:

The eight pneumatic functions coming from the distribution module included the front arm and bucket, two joints in the rear arm, outriggers, rear arm rotation, and both a bucket and a "thumb" on the end of the rear arm. The rear bucket was a 3D-printed copy of the old, old 4700 bucket, since it seemed to be the one in the best scale for this model. Everything worked well, with the exception of the rear arm rotation, which was too powerful and tended to self-destruct because of the way the cylinders never reached the end of their strokes naturally. The RC valves didn't have the proper reaction time for fine control of any of the functions, which would have been a big downside for working in practice, though this could have been mitigated by using a smaller, on-demand compressor, rather than the big 2L air supply I was typically using.

Spoiler

With my power supplies being a MouldKing 6.0 unit and a PU Technic hub, I ended up having this rather unique controller combination!

 

Anyways, I was pleased with this model! It was challenging to control precisely, but it succeeded in my main goals of including an enormous amount of RC capability and having an interesting pneumatic function-splitting device!

More images at: https://bricksafe.com/pages/2GodBDGlory/backhoe

Edited February 5, 2024 by 2GodBDGlory

[Milan]

Always great to see another backhoe
I am constantly amazed to see how many functions there are in the real machine, and even more amazed to see builders incorporating them in a model, like this one.

Yeah, wheelbase is a bit longer, but since you chose to make it your own, there are no constrains.
There are also a lot of real life backhoes that have a very long wheelbase, especially those with articulated chassis.

Scale would be around 1:10-1:12?

I built, I think, 3 JCB backhoes so far, always 1:13, and always the 3CX and 4CX.

And ofc, planning for at least two more

Frontpaged.

[Maaboo the Witch]

Oho, this 🐕 rocks! Amazing work!

[Ryokeen]

That is some serious technic you packed in there, quite impressive i have to say sir.

[gyenesvi]

Wow, that's an astonishing amount of functions in such a size! That RC pneumatic selector is pretty cool, and while it might be a bit sketchy in the current implementation (accuracy of positioning the switches), I think the concept could be made robust using parts designed for this purpose. I wonder how smooth the operation would be with an RC pump.

[Jundis]

This thing is again packed to the max (and beyond :D)!

I actually envy the speed of the pneumatic actuation you achieved with the air bottle. This was my biggest hurdle in all of the pneumatic models I've done so far. I'd wish Lego would provide us with a better pump :-/

11 hours ago, Milan said:

And ofc, planning for at least two more

I'd be very curious about your models, did you post them here? I always saw you as the Admin, never as the builder :D

[Mikdun]

That's amazing, dense build. Impressive!

The chassis proportion are a bit off, but hey, that's Technic forum not Model Team! Oh, wait... 

For me great build. I adore the pneumatic function switch. It shows how much we need some more advanced pneumatics.

[EWay]

Incredible that you've packed so many functions into it. Very impressed with the pneumatic function shifter, and the windscreen wipers are really cool!

Pardon my ignorance, one question I have is about the driving ring on the diff lock. Would the old 2L ring (part 6539) not have worked here? I haven't done much in the way of Technic MOCs in recent years and don't have any of the new fangled differentials, so maybe it's not compatible or something...

[dhc6twinotter]

This is a really fantastic model!  I love how you think outside the box with your builds, and this is no exception.  You’ve managed to pack a lot of functions into a really tight spot.  

I built a 3CX years ago, although I didn’t have the side-shift arm, thumb, or 4-speed gearbox.  I’m currently working on a smaller scale PU version now.  I think backhoes and road graders are probably some of the most challenging machines to build out of Technic.  There’s just no room for anything.  You’ve pulled it off nicely.

[2GodBDGlory]

18 hours ago, Milan said:

Always great to see another backhoe
I am constantly amazed to see how many functions there are in the real machine, and even more amazed to see builders incorporating them in a model, like this one.

Yeah, wheelbase is a bit longer, but since you chose to make it your own, there are no constrains.
There are also a lot of real life backhoes that have a very long wheelbase, especially those with articulated chassis.

Scale would be around 1:10-1:12?

I built, I think, 3 JCB backhoes so far, always 1:13, and always the 3CX and 4CX.

And ofc, planning for at least two more

Frontpaged.

I just did some math, and found it to be about 1:13.3, based on tire size. Thanks for the frontpage!

6 hours ago, gyenesvi said:

Wow, that's an astonishing amount of functions in such a size! That RC pneumatic selector is pretty cool, and while it might be a bit sketchy in the current implementation (accuracy of positioning the switches), I think the concept could be made robust using parts designed for this purpose. I wonder how smooth the operation would be with an RC pump.

I think it could be improved a lot with some smoother parts for it to slide into, and using the newer pneumatic valves through drive from their axle holes would take out a lot of slack--I just didn't have enough of those to try it. I expect it could be controlled a lot more precisely with an RC pump, but I never did a whole lot of testing with my onboard pump. It'd be interesting to know, since it could have been a good option, but I've already taken the model apart, so it's too late now!

4 hours ago, Mikdun said:

That's amazing, dense build. Impressive!

The chassis proportion are a bit off, but hey, that's Technic forum not Model Team! Oh, wait... 

For me great build. I adore the pneumatic function switch. It shows how much we need some more advanced pneumatics.

Thanks! It does feel like a lot of complexity for what could be a relatively simple problem

6 hours ago, Jundis said:

This thing is again packed to the max (and beyond :D)!

I actually envy the speed of the pneumatic actuation you achieved with the air bottle. This was my biggest hurdle in all of the pneumatic models I've done so far. I'd wish Lego would provide us with a better pump :-/

I'd be very curious about your models, did you post them here? I always saw you as the Admin, never as the builder :D

I'm quite pleased with the air bottle! It provides plenty of air, and didn't cost me anything to make, as opposed to using an expensive air compressor.

2 hours ago, EWay said:

Incredible that you've packed so many functions into it. Very impressed with the pneumatic function shifter, and the windscreen wipers are really cool!

Pardon my ignorance, one question I have is about the driving ring on the diff lock. Would the old 2L ring (part 6539) not have worked here? I haven't done much in the way of Technic MOCs in recent years and don't have any of the new fangled differentials, so maybe it's not compatible or something...

Thanks! Glad to see you like the windshield wipers. One would think that old 2L ring should work for the diff lock, but all of the clutch gears from 2015 on, including these differentials, has a larger internal lip that doesn't allow the old 2L rings to engage with them.

30 minutes ago, dhc6twinotter said:

This is a really fantastic model!  I love how you think outside the box with your builds, and this is no exception.  You’ve managed to pack a lot of functions into a really tight spot.  

I built a 3CX years ago, although I didn’t have the side-shift arm, thumb, or 4-speed gearbox.  I’m currently working on a smaller scale PU version now.  I think backhoes and road graders are probably some of the most challenging machines to build out of Technic.  There’s just no room for anything.  You’ve pulled it off nicely.

Thanks! It'll be interesting to see what you come up with!

[allanp]

Well how did I miss this? Very well done on this crazy dense build.

[Aleh]

Did you hire a specialist to manage all these insane pneumo hoses? Welldone!

[2GodBDGlory]

45 minutes ago, Aleh said:

Did you hire a specialist to manage all these insane pneumo hoses? Welldone!

Thanks! The hoses were a nightmare... I think I spent close to a week on them

[Paul B Technic]

This is next level greatness :)

[1gor]

About second Servo problem; I have noticed same problem with my Fastrac that was planned to have several steering modes. The same servo I use now in prototype of smaller scale Fastrac which has only front wheel steering and it works just fine; perhaps there is some issue with receiver? Or not enough current?

Backhoe looks cool

Edited February 8, 2024 by 1gor

[Mikdun]

5 hours ago, 1gor said:

The same servo I use now in prototype of smaller scale Fastrac which has only front wheel steering and it works just fine; perhaps there is some issue with receiver? Or not enough current?

Polarity switch has not good contacts?

[1gor]

9 minutes ago, Mikdun said:

Polarity switch has not good contacts?

I didn't use polarity switch, just PF receivers (the same with V1 and V2) so I suppose that I need 9V battery box (6 rechargibles with 1.5V), so I switch to smaller scale models...

[gyenesvi]

55 minutes ago, 1gor said:

I didn't use polarity switch, just PF receivers (the same with V1 and V2) so I suppose that I need 9V battery box (6 rechargibles with 1.5V), so I switch to smaller scale models...

Yeah, but this build was using a switch, so here that may have been the problem :) I guess it's still easy to test out even if the parts are not built into the model..

[1gor]

29 minutes ago, gyenesvi said:

Yeah, but this build was using a switch, so here that may have been the problem :) I guess it's still easy to test out even if the parts are not built into the model..

I was actually sharing my situation in irder to give a hint to a problem oerhaps, but you are apsolutely right it could be polarity switch. I have one ftom 8297 set abd it can only be used as extension cable...

[Mikdun]

2 hours ago, 1gor said:

I didn't use polarity switch, just PF receivers

I assumed you are using polarity switch to change modes.

[1gor]

1 hour ago, Mikdun said:

I assumed you are using polarity switch to change modes.

Just controller and playing with sticks 

[2GodBDGlory]

Huh, that's an interesting thought! I know I have several faulty switches, but it was always just that one position of the switch didn't work at all, while the other position worked fine with both directions of current flowing through.

I suppose it could be an odd switch issue, but given that most of my Servos have failed at some point, been taken apart, and convinced to work again at some point, I didn't think to look for problems in other areas!

I could try to check that out, but now that the switch and servo have been thrown into my mixed electronics bin, it might be hard to tell which ones it was that were on the model

Thanks for sharing!

[R0Sch]

Amazing work @2GodBDGlory! And here I was thinking that 8455 was already pretty darn perfect.

[Anto]

Wow, the amount of functions you packed into this model is unbelivable! Even though the mechanism to select the pneumatic switches is not 100% reliable, that's a pretty good concept, never seen before!

Now I want one!

[Mr Jos]

Very nice model with a lot of functions. Good to see you had some inspiration from my model, which you credited, thanks! You managed to make it a lot smaller which is good for these scale models. Mine has been running with 5 valves for 3 event days (8hours each) now, and has broken 2x total.(chain opened up as something got stuck in the selecting of a valve).

Really like these Lego pneumatic MOC's.