This is my newest lego creation, the tow truck from Johnny English! You can see pictures about the real thing here. Hope you like it! :)
The truck is completely remote controlled. It has six functions, but only four motors. Two L motors and one M motor drive the functions, and one M motor drives the gearbox. At first you can control the steering, the driving and the outriggers, after using the gearbox the crane’s rotation, the height and the length.
The truck is 47 cm long and 15 cm wide and very heavy and crammed with gears, motors, gears, axles, beams and gears...
I made a funny video, which shows how the truck works (with real speed), but has a story, too! :D
You can find pictures about the buggy and the figures here and here.
Pictures of the truck:
This is the remote control. I printed a guide, which helps to find the right arm and right direction.
Between the two platform I didn’t cover the gears, so it’s possible to see them during working. It was a real challenge to put the gearbox in this small place and bring every axles into the right direction and place.
The outriggers are necessary, whithout them the weight of the buggy causes an arch in the chassis.
The most difficult part of the truck was the crane.
There was an important requirement. The frame which holds the buggy has to stay parallel with the truck to keep the buggy in right position. You can see an axle which goes at the middle of the crane. It starts at the turntable of the chassis with a 8 toothed gear and ends at the turntable at the top of the crane. The gear ratio is 1:1. There are 3 universial joints and a lot of gears in this axle, so the efficiency is not 100%, but quite good.
At the end of the crane you can see a long black axle. When the crane becomes longer or shorter, the 16 toothed light grey gear slides on it, so the driving of the parallel-keeper is independent of the length of the crane.
The photo below shows how the crane becomes longer, or shorter. The worm gear drives an axle with a bush on each side. They coil up a rope and coil down another. These ropes throw half bushes pull the moving part of the crane. The crane can be longer with 6 studs.
The parallel-keeper is outside so I had to use a 8 toothed gear for the crane rotation in the inner side of the turntable (near the axle of the linear actuator and the axle of the longer-shorter mechanism) and the turntable has too much friction. Because of these things the crane couldn’t rotate under weight.
The solution has several parts: the gear ratio makes the rotation very slow, the outriggers hold the chassis without distortion, little fat on 2 places in the turntable, light car (a buggy hasn’t got a body made of heavy lego plates, only four wheels and a roll cage, maybe steering wheel ;)), it is forbidden to rotate the crane if it is longer (the arm of the force must be the shortest) and the contact places of the actuator’s ends are also very important.
(If you are a detective or simply have good memory, you may remember, that the crane were longer during the rotation in the video. The reason is that the road wasn’t horizontal, so it helped the rotation.)
The black force is the buggy’s weight. The crane is held at the contact of the actuator and the top part of the crane. The ratio of the green and orange lines decides the ratio of the red and blue forces. The red force has to be bigger, because the surface covered by fat is bigger here, than at the other place.
The truck is not perfect, but I worked a lot and rebuilt it many times so I’m very happy, that it’s ready and works! :)
... I did miss this, sorry mate. I have been away and moving house so Lego has taken a back step. This is Lego Technic at its very best best, the gearbox is very impressive. I see you are still on track to becoming an engineer. Great work.
A good and very realistic looking build. The proportions look just right and I like the checkered band around its load bed. The video shows off the working functions brilliantly. It's also possibly the funniest video of a car being towed away that I've seen :) Both the MOC and the presentation are cleverly thought out and realised.
Thanks for the first comment Alex! :). I built it near the school, so I had not too much time a day. Planning was fast, but the building was very slow. I started with the crane and its things in the chassis. But I had to take apart the whole construction many times, because it didn't work. I think it took approx one month!