[MOC] Caterpillar 226B Skid steer loader

[johncarpenter]

This is the skid steer loader that I built last year. It was my second build after my long dark ages.

I selected the Caterpillar 226B as a reference and selected the 62.4 wheels for this build.

I realized only much later that the scale (especially the width) was very challenging. If I were to build this again, I would probably compromise and make it 2 studs wider. However, the biggest challenge on this build was something unexpected: the center of gravity.

I started off with the power functions battery box. Due to the size of the model, the only place to put it was at the very back. With the first mockup, it was already clear, front wheels were never going to touch the ground.

To fix this, I switched to the AAA battery box, as the AAA batteries weigh much less. This improved the balance, at least it sat still on all 4 wheels. However, it still did a wheelie every time it started to drive.
My final card to play was replacing the two IR receivers with an Sbrick, to have less weight at the back. This improved things to the point where I thought that the whole model could work. It was still a wheelie monster, but there was hope.

After that, I revisited each part of the model and redesigned to have as much weight as possible at the front. The bucket was brick built to have more weight at the front. The forward chassis had all empty spaces possible filled with liftarms. All empty holes were filled with pins, axles. I could see that I was getting there, but had to take some more extreme measures. In some places I used two thin liftarms instead of a normal liftarm. The cabin was designed to have smaller bricks at the front and so on... It was ridiculous, but in the end, it all helped, and the balance was fixed.

Here are some more pictures of the finished model:

The arms and the bucket work really well and quick enough. The drive is the weak point on this model, as it is only with M motors. Driving full speed is fine, no problems there. However, they have issues starting to drive with only part throttle, especially with 1.2v rechargable batteries.

Due to the balance issue, I considered abandoning this project at several points along the way. However, I'm glad that I kept going, and I'm really happy about the result.

Technical details

• Length: 30 cm
• Width: 13 cm
• Height: 17.5 cm
• Weight: 1.16 kg

Power functions

• 2 x Power Functions M motor for skid steer drive
• PF L motor for arm lift
• PF L motor for bucket tilt
• PF AAA Battery Box
• Sbrick for control

Here is the video with the model in action:

 

Edited February 18, 2021 by johncarpenter
added tags

[Maaboo the Witch]

Very cool! It'd look great with the tyres from 42122 as well. 

[kieran]

Looks great, nice and compact with great functionality 

[jorgeopesi]

The best I have ever seen very good job, movement, playable, realistic it has everything I like.

[Jundis]

What a great clean build! I also loved the wheely :-)

1 hour ago, Maaboo35 said:

Very cool! It'd look great with the tyres from 42122 as well. 

Exactly my first thought

[A_C]

Thanks for the sharing, especially how you overcome the size problem. Well done.

[trekman]

Nice clean lines, and very tidy integration of the bucket tip.  I am glad that you did not use larger motors, as your drive train to the wheels could not cope with higher torque.  But performance is good anyway.  Well done.

[weavil]

Nice clean build! Looks like you shrunk a real one.

[Jurss]

Nice loader, battery (S-brick) is well integrated.

8 hours ago, Maaboo35 said:

t'd look great with the tyres from 42122 as well. 

Don't think so, in this case they would be too small, and they are proportionally too wide.

[mpj]

Nice and clever design, I like it very much! You only need some Cat stickers 

[johncarpenter]

Thanks everyone for your comments, I appreciate the feedback!

At the time I built this, those tires were not yet available. But hey, I've not yet disassembled it, and I have 4 of those tires now, so why not try them out:

And here is one with some of the internals exposed.

To be honest, I really like these wheels on the skid steer, thank you for the suggestion. Even though they are a tad small, they look really fitting. The smaller diameter might make the job of the M motors easier as well. This has got me thinking about making a new video now, with these wheels :)

[jorgeopesi]

I think you can put the front wheels of the batman car from Lego, I think they have a similar size and they are wider.

[pdw]

Nice job.  I built something based on a 216B at the end of last year so very interesting to see how you tackled it.  I struggled particularly with the shape of the rear, and I like what you've done there.

I also struggled with balance, although I had the battery box over the wheels which helped. 

15 hours ago, johncarpenter said:

they have issues starting to drive with only part throttle

I was struggling with this in another model, and discovered that if you drive them with a lower PWM frequency they work much better.  Not sure which app you're using, but I have a custom build of BrickController 2 for Android that allows me to set the PWM frequency on an SBrick.

 

Edited February 11, 2021 by pdw

[ralphie]

Nicely done, very compact especially on the bucket arms.

[Maaboo the Witch]

It looks better with the Jeep tyres in my opinion.

[johncarpenter]

@pdw, any pictures of your 216B? I would be interested to see how you tackled it. Thanks for the hint on driving the M motors.

 

@jorgeopesi I'm quite sure the batman front tires will foul both the rear wheelarch and the linear actuators at the front. The initial tires barely cleared both. However, those tires do look quite nice. I'm thinking about doing another skid steer in a slightly larger scale, and this seems like the perfect tire for it.

[jorgeopesi]

2 hours ago, johncarpenter said:

@pdw, any pictures of your 216B? I would be interested to see how you tackled it. Thanks for the hint on driving the M motors.

 

@jorgeopesi I'm quite sure the batman front tires will foul both the rear wheelarch and the linear actuators at the front. The initial tires barely cleared both. However, those tires do look quite nice. I'm thinking about doing another skid steer in a slightly larger scale, and this seems like the perfect tire for it.

You are right, another bigger one whit them will be even better having more room from everything.

[pdw]

13 hours ago, johncarpenter said:

@pdw, any pictures of your 216B? I would be interested to see how you tackled it. Thanks for the hint on driving the M motors.

I did this as a Christmas present for my daughter, and it was put together fairly quickly as I needed to get parts ordered.  It was my first attempt at doing something to scale, and was done entirely digitally - my daughter received a box of bits and instructions for a model that had never been physically built.  A bit of a risk, but aside from a quick redesign to get the battery one stud forwards for balance it went pretty well.  It's got two L motors for drive, behind the rear wheels,  two M motors for the arm, controlled by an SBrick and the AA battery box.

I was happy with result, but there's definitely things I'd improve or do differently with a bit more time.  I realised too late that I'd messed up the scale, and both the roof and rear section are too high.

The large LAs are too long, but I couldn't get sufficient height with the medium LAs.

Looking at some of the details, I like how you kept the arms to 2 studs wide.  I wanted to drive the tilt mechanism from underneath the arm pivot, as you have done, but the angle of the arm when lowered was just slightly too steep and the gears would collide.

The system bricks for the mudguard and curved section behind the rear wheels work really well - I recognised it instantly as a Cat before I saw the topic title!

Filling in the lower section behind the wheels with yellow beams also makes a surprisingly big difference to the appearance.  

 

[johncarpenter]

Nice build, in a slightly bigger scale. I would likely use this scale for my next skid steer build, enough space for batteries and motors without being giant. Your layout is definitely better for the center of gravity, having the BB under the seat is good.

It's interesting that we came to almost exactly the same solution for the bucket mechanism.

I also had the issues with clearance of the bucket drive and the linear actuator. Initially, the linear actuator was attached one stud higher on the chassis. This both looks better in the lower position because it ends up horizontal and allows more lift height at the top. However, with this geometry, the linear actuator tended to run into the gears at the top of the range, so I had to lower the linear actuator attachment down by 1 stud. I think I built the arm / bucket mechanism there about 7 or 8 times before I got to this geometry and got everything working reliably without gears skipping etc...
 

[pdw]

I didn't have that particular issue because the LA pivot is forward of the upper arm pivot, but the flip side of that is reduced reach.  I came to the conclusion that the hydraulic cylinders on the real thing have far less "overhead" than a Lego LA i.e. they get much closer to doubling the length between pivots when extended, so it's always going to be difficult to replicate the geometry.