[MOC REVIEW] PF Backhoe by Jurgen Krooshoop

[Blakbird]

Jurgen Krooshoop's backhoe has been on my build list ever since he first published it in 2012. My main excuse for not building it earlier is simply expense. This is a huge model with lots of Power Functions and plenty of rare parts as well. However, whenever there was a lull in my schedule my mind returned to this beauty, and finally I could not resist any more. It took a considerable amount of time to acquire the necessary parts, with things like the Power Puller wheels being a particular problem. The renders below show the inside and outside of the model.

     

Every model starts as a pile of parts, and this is quite a pile. We have nearly 2000 parts here which, by itself, it not vastly greater than many Technic MOCs. But the list of Power Functions components is what really sets it apart.

• 1 rechargeable battery
• 3 set of LED lights
• 7 M motors
• 1 XL motor
• 4 IR receivers
• 2 PF extensions
• 9 Linear actuators

     

 

     

You will immediately notice the 8 motors, but this model actually has 9 motorized functions which is accomplished in a clever way. Neither the L motor nor the servo existed at the time this model was made. In retrospect, both of them could have been useful. Rare parts include the flex axles, Power Puller wheels, and 10x18 bucket.

Next I'll show a bunch of pictures of the build process. As is usual for Jurgen, his instructions are excellent with lots of arrows and even show most of the wire routing. Following the instructions was no problem at all. The model is very durable and well braced, at least as much as possible for something this heavy. I did find one error in the instructions in which a 12 tooth double bevel gear was missing. By the time I realized it, I had to tear apart about 50 steps worth of structure to get to it. It is possible that I have a pre-release version of the instructions.

Here is the main chassis with gearbox functions and motors. As you can see, there is a LOT going on here.

     

 

     

 

     

Here is the completed main body without the front or rear attachments. I really like the curved fenders and the way the battery box is hidden under the hood but still easily accessible.

Here is the front loader assembly.

When building the rear excavator, I took apart the turntable and lubricated it with silicon spray prior to installing it. I was glad I did because the boom is very heavy and it worked super smooth this way.

Here is the completed model. I'll run you through the functions and my thoughts on each of them:

• The front axle is pendular. The torque tube parts did not exist yet, so that means the weight of the model is resting on the steering axle. Notionally this is a problem but the model does not seem to suffer for it.
• The front wheels steer with a rack and pinion system driven through a clutch gear. Sometimes if you try to steer when stopped the clutch gear will slip. The steering is geared to be very fast which is a bit of a problem for control because it is very difficult to get the wheels to stop in the straight ahead position. This is where the servo would be really helpful, and could probably be easily retrofit given that the motor is just hanging off the side and easily accessible.
• The rear wheels are driven by an XL motor through a differential. The drive train is pretty direct and VERY fast. In fact, it is so fast that you can't really drive it without the proportional train remote. With that one, it drives very nicely. I was a bit surprised how well it works with only 1 XL motor given the weight.
• The loader boom raises with a pair of linear actuators. The power and speed are reasonable, however the actuators don't retract far enough to let the bucket reach the ground, so you can't really scoop up anything off the ground with it.
• The bucket tips with a pair of linear actuators which have plenty of power. The use of linear actuator brackets in the gear train which are not paired with actuators was new to me. The bucket has enough power to lift the front wheels off the ground if the bucket is tipped while the boom is down.
• There are outriggers in the rear. These are just vertical linear actuators driving directly. They can lift up the rear of the model which is impressive given the weight of the excavator. A clever system is used to keep the rod end from rotating while extending.
• The excavator boom slews 180 degrees (not 360 like Jurgen says in the video) using a worm gear driving the ring gear of the turntable. There is a clutch gear on this system to protect to motor when end of travel is reached.
• The excavator boom raises with a single linear actuator. This is the weakest part of the model. It only uses an M motor so the actuator needed to be installed with a significant mechanical advantage to have the necessary power. This means that the motion is slow and the range of motion is small. The UP position of the boom is very scale accurate, but the DOWN position of the boom is not low enough to reach below grade so you can't "dig". It works acceptably given the constraints. I think it would be much improved with an L motor that would allow a different actuator position. Note that this function is driven from inside the loader so the drive axle passes through the turntable.
• The dipper is driven by an M motor inside the boom and a linear acuator. The drive is nearly direct (1:1) and works very well.
• The bucket is driven by an M motor inside the dipper and a linear actuator. The bucket is really too big for a backhoe, but there is not a great alternative. Range of motion of the bucket is very good.
• Finally, there is a two position gearbox in the chassis driven by a final M motor. Unlike 8043, the motor has no trouble switching the gearbox under any circumstances the model encountered. Most functions are available all the time, but you can switch between operating the front or rear boom and bucket.

     

To give you an idea of how big this model is, here it is next to some other backhoes. As you can see, it is enormous.

     

 

I'd certainly recommend this model to anyone who can come up with the required parts. It was a lot of fun to build and use. The only real complication is the wiring, which is nearly always true of a model with so much PF. There is quite a pile of wires inside the cabin by the time you are done, and stowing it all without interfering with any gears can be tricky. If I was doing it all over again, I might omit the lights from the roof because those were the hardest to route and stow.

Thanks to Jurgen for making this available to the community. It is a great model.

(Bigger versions of all pictures at my Bricksafe.)

[jantjeuh]

This is also on my to-build list, I already have all the parts. By the way, what was the error in the instructions? I hope to avoid it myself ;-)

Edited July 8, 2014 by jantjeuh

[Tommy Styrvoky]

Cool model, how do you do your renders with the PF cables ?

Do you use LDD or ldraw ?

Edited July 8, 2014 by Tommy Styrvoky

[Alasdair Ryan]

I built this backhoe a couple of weeks after it came out,I only needed to spend about 30 uk pounds on parts.

[plew2000]

Wow this is realy cool.

[Rishab N]

I was wondering when you would build this. It only seemed fit for your already amazing collection.

[dhc6twinotter]

Thanks for the great review! Looks like a really well built model with some great features.

[afol1969]

This backhoe is also on my build-list since long time. It's amazing to put so many functions in a complex and compact construction!

Thanks for the great and detailed review

Greetings

Alex

[legolijntje]

This model is also on my build list for a looong time. The only problem are the Power Puller wheels. I have about 99% of the other parts. I don't want to spend like €100 for 4 wheels (I want 4, although you only need 2 in the model). So, I'm waiting for a good deal for either the wheels or a set with 4 of the wheels...

The model is really nice though, and I've seen the instructions, and they are also very nice. A lot of work has gon into both

[IJsmuts]

Amazing MOC, in my eyes one of the best out there! And im already collecting the parts. Only need the PF stuff. Think i will give that myseld for xmas!

Very nice review Blakbird, thanks. Is it possible to make a picture from the backhoe next to e recent flagship? I would like to see the size and i dont have the other backhoes

Edited July 9, 2014 by IJsmuts

[jantjeuh]

This model is also on my build list for a looong time. The only problem are the Power Puller wheels. I have about 99% of the other parts. I don't want to spend like €100 for 4 wheels (I want 4, although you only need 2 in the model). So, I'm waiting for a good deal for either the wheels or a set with 4 of the wheels...

Keep a good eye on Marktplaats.nl for the 8466 set, that's how I got four PPs for cheap.

[legolijntje]

Keep a good eye on Marktplaats.nl for the 8466 set, that's how I got four PPs for cheap.

I do! But it seems I always miss the good deals

[jantjeuh]

I do! But it seems I always miss the good deals

Yeah, you have to be a bit lucky. I got a near-mint 8466 set for only 60 EUR, little did the seller know that the tires alone are worth 80 EUR easily

By the way, Blakbird, thanks for doing these MOC reviews. Especially now that creators (rightly so) charge for instructions, reviews are a good thing.

Edited July 9, 2014 by jantjeuh

[kristl]

I also build this MOC and it's great. I think it's the best backhoe ever designed with Lego, because despite it's size and weight it's still functions very well. This one from Pippasseyoyo might be better looking but the front loader doesn't reach high enough and the backhoe is not supported enough beacuse of the sideway mechanism which is a nice feature but it is hard to make it strong with Lego. (

). The two things that Blakbird mentioned about the front loader and rear backhoe not reaching the ground can be fixed by sacrifising some lifting height of the front loader and bachoe. The problem is the weight and the soft PP wheels, which means the whole machine leans to the back and is approximately two studs lower at the back. If the tires could support the weight without being compressed the front loader would reach the ground. Edited July 9, 2014 by kristl

[skriblez]

Thank you very much for this review. Seems i have to add this to my list of mocs that needs building

[Duky]

This model is also on my build list for a looong time. The only problem are the Power Puller wheels. I have about 99% of the other parts. I don't want to spend like €100 for 4 wheels (I want 4, although you only need 2 in the model). So, I'm waiting for a good deal for either the wheels or a set with 4 of the wheels...

The model is really nice though, and I've seen the instructions, and they are also very nice. A lot of work has gon into both

maybe you can use a tyre from the crawler 9398

[jantjeuh]

Nevermind, I was mistaken!

Edited July 9, 2014 by jantjeuh

[Zerobricks]

Tires in front are 9398 tires, that's how big this model is. You really need power pullers for the rear tires.

No they are not...Besides there were no yellow rims for 8297 wheels at that time.

[jantjeuh]

Whoops, you're right. Anyway, I think the 9398 tires would look too skinny.

Edited July 9, 2014 by jantjeuh

[Kladovec]

I also build this MOC and it's great. I think it's the best backhoe ever designed with Lego, because despite it's size and weight it's still functions very well. This one from Pippasseyoyo might be better looking but the front loader doesn't reach high enough and the backhoe is not supported enough beacuse of the sideway mechanism which is a nice feature but it is hard to make it strong with Lego. (

). The two things that Blakbird mentioned about the front loader and rear backhoe not reaching the ground can be fixed by sacrifising some lifting height of the front loader and bachoe. The problem is the weight and the soft PP wheels, which means the whole machine leans to the back and is approximately two studs lower at the back. If the tires could support the weight without being compressed the front loader would reach the ground.

This is really great model. My no. 1. I build Jurgens backhoe V1 (with his help) and added Pippasseyoyo´s sideway mechanism. I solved slow motion with rear boom with third M motor in it.

[Blakbird]

This is also on my to-build list, I already have all the parts. By the way, what was the error in the instructions? I hope to avoid it myself ;-)

I will try to remember to show you the exact page and step when I get home from work tonight.

Cool model, how do you do your renders with the PF cables ?

Do you use LDD or ldraw ?

All my CAD work is with LDraw tools. The editor is MLCAD. Wires and synthesized with LSynth. In this case, Jurgen built the model and synthesized the wires himself. All I did was render the result so he gets the credit.

Very nice review Blakbird, thanks. Is it possible to make a picture from the backhoe next to e recent flagship? I would like to see the size and i dont have the other backhoes

Sure, which flagship did you have in mind? Let me know what you want and I'll take a picture.

[Duky]

No they are not...Besides there were no yellow rims for 8297 wheels at that time.

already have the back wheels. i only need the 2 back tyres...

Unfortunately, i have only 9398 Crawler Tyres . But no way i will pay over 20 Euro's for one Tyre.

[IJsmuts]

Sure, which flagship did you have in mind? Let me know what you want and I'll take a picture.

Thanks! I would like to see it next to the unimog and hoping its around the same scale...

[Blakbird]

Thanks! I would like to see it next to the unimog and hoping its around the same scale...

I would say it is about the same size, but not the same scale. A real Backhoe (depending on model) should be considerably larger than a Unimog.

[jantjeuh]

I will try to remember to show you the exact page and step when I get home from work tonight.

Alright!