Backhoe

This project started with a gearbox and with this gearbox in my hand I started thinking what I should do with it. Somehow I figured a Backhoe would be fun to build so that's what I did.

I've always had a bit of trouble getting a nice gearbox done so I sat down and focused on gearboxes one night. I did not come up with a good version since the high gear also had to turn the low gear gear train. I realized I had to separate high and low gear and this tractor is what I did with the final gearbox.

I made the gearbox with MLCAD and had to make some fixes on it later. Here's the finished version:

While constructing I looked at some pictures of a Caterpillar 416C. Photos can be found here, but I don't know for how long since it's an item for sale. I used the pictures for inspiration only, this is no scale model.

As always I went for the RC stuff and I've been thinking about a way to milk more functions out of my five channel radio. I came up with a solution that let me control eleven functions via both polarity and pneumatic switches.

Facts

Weight: Approx. ~4kg (8.818lb)
Total length (including blade and backhoe {folded}): ~79cm (31.102")
Height cab roof -> ground: ~27cm (10.630")
Width: 24cm (9.449")

Functions

It has two different operation modes, one that let's me drive the Tractor and lift/lower the blade and also to switch between the high and low gear and another that let's me operate the digger arm. The selection of modes is also controlled via RC.

Operation mode #1 - Drive mode

Function	Motion/State	Powered by
Drive	Forward/Reverse	Dual 9V motors
Steering	Left/Right	9V motor
Gear	High (~1:2) /Low (~1:150)	Pneumatic cylinder
Blade	Up/Down	Dual pneumatic cylinders in parallel

Operation mode #2 - Dig mode

Function	Motion/State	Powered by
Digger arm	Left/Right	Micro motor
Digger arm	Up/Down	Dual pneumatic cylinders in series
Digger arm	Bend Up/Down	Pneumatic cylinder
Bucket	Up/Down	Pneumatic cylinder

Switching between the two operation modes also triggers some additional functions between two states

Function	Motion/State	Powered by
Outriggers	Up/Down	Dual pneumatic cylinders in parallel
Headlights	On/Off	Polarity switch
Worklight	On/Off	Polarity switch

All in all eleven different remote controlled functions.

We start off with an overview picture displaying the whole thing.

Pretty self explanatory :)

Front view, I'm rather satisfied with the design on the blade. I've been thinking about doing a blade this way and when I made a MOC that could be equipped with one I could no longer resist :) I must say I'm fairly shocked with the amount of black double bent liftarms I own (and they're all there). I knew they were plenty but not that many...

And the right side, surprise! It looks just like the left :-O

What defines this model - The backhoe. It's no easy task to build those things but I'm satisfied with how it turned out. The rubberbands are there to keep the boom up when the pressure goes out of the system.

I'm really satisfied with the outriggers.

Here you can also see the worklight that turns on when selecting "dig mode".

Looking down on my creation are you? :)
The exhaustpipe is connected to the main power polarity switch. If turned a little the Backhoe powers up or down. The two lights on the roof blink when the power is on.

Bottom out :) There is no bottom - I had trouble covering the top with plates...

I'm not that satisfied with the cab. First I got disappointed when I realized I needed the space for the servos and stuff and then the polarity switches refused to fit inside it...

At least I got some side mirrors and railings there :)

Rear mudguards, it took some tinkering but they finally turned out OK. The 1 x 4 plate that looks loose is connected to a pair of ½ pins that locks it between the 4 x 4 plates.

And here's the front mudguard. It's attached to the wheel mount and turns with the wheel. I like this setup.

A blurry picture of the outrigger. The function of these is terrific! It's probably the one single part I'm most happy with on this MOC. As mentioned they automatically lowers when I switch to "digging mode" and rise when switching to "drive mode". Splendid!

The outriggers again. The red LEGO in this picture is the micro motor driving the turntable with the backhoe on. Notice the medium pulley wheels on the drive axles, an attempt to stiffen the axles up a bit.

If you've seen my RC MOC's before you know I have some absurd form of fetish for taking pictures of the RC On-Off switch. Here it is :) It's hidden under a hatch this time.

The steering setup. I stole this design from 8479 and adapted it to my chassis width etc.. It works pretty OK steering the two wheels unparallel but still keeping them parallel when driving straight. This allows for better steering.

And going to the bottom with the steering, here you can se the engine that steers. It's connected via a wormgear for speed reduction and a z24 slip gear to save the design. The two z24-medium pulley sandwiches in the top of the picture is part of the pneumatic compressor.

The ground clearance is nothing to brag about so I suggest you read about my next picture instead :) The sheet used as backdrop is no help to me here since it's "bubbled" up a bit.

This is the backhoe arm in it's extreme left position. Of course it can be swung around 180 degrees to the far right. Swung and swung, it's a pretty slow motion and the micro motor tend to jam occasionally...

This is as far as the backhoe can reach backwards, it could have been more but then it would not fold nicely so this is a compromise I'm pleased with.

I used double pneumatic cylinders in series to get a better/longer stroke to this motion and it works as intended.

Curling it up.

Some detailed pictures of the blade. It's made of 37 double bent liftarms and is 39 studs wide. I also just noticed it's dusty :)

The box connecting the blade and tractor. I did not work that much on this part hence the result.

This is the total amount of lifting capabilities. Not much :) Also the blade is so heavy and the pneumatic design so poor that it needs a little HOG help to get there.

Scale comparison. This is a kid who has one of his best moments, he get's to sit on the tractor while someone takes pictures ;)

Frame with a gearbox with pneumatic control, one motor and all four wheels.

Time stamp: 2002-03-02 11:35

Outriggers in place, compressor (based on Ralph Hempel's design) and the second drive motor. The steering is also finished. At this stage the high gear worked splendid. I added some beams over the dif to keep things in one part while driving in the low gear.
Time stamp: 2002-03-02 19:08

Backhoe is finished.
Time stamp: 2002-03-02 20:47

The micro motor and turntable for the backhoe is in place.
Time stamp: Unknown.

Blade done.
Time stamp: 2002-03-02 23:06

I realized the low and high gear made the outshaft turn in different directions so I added a polarity switch to automatically change the direction on the motors. Problem solved.
Time stamp: 2002-03-03 10:52

After a few unsuccessful attempts installing most of the servos into the body and thus leaving the cab I gave up and went for the space inside the cab. I made this control tower with the different setups needed. Two controls per servo and five servos = 10 controls.
Time stamp: 2002-03-03 22:09

All functions hooked up and working.
Time stamp: 2002-03-10 15:12

Control tower installed and working.
Time stamp: 2002-03-12 12:52

Model finished.
Time stamp: 2002-03-20 19:05




Here are some of the notes I did while planning/building this MOC. They're all about making the controls work like wanted and how to connect the pneumatics and electronics.

Here's the control scheme. I hope it's clear enough so that you can understand it. Each servo controls the switches that are located on the left and right side of the servo. I made dual pneumatic and electric systems.