Hot Bulb Pneumatic Tractor
A lego pneumatic tractor based on a hot bulb engine Lanz tractor. Features drive, single pneumatic engine, adjustable ignition point, steering and suspended seat.
I wanted for a long time to build another tractor to improve the previous and use a single engine with inertia wheel as on my pneumatic machine. The result is here : a pneumatic single engine tractor with a special feature : adjustable ignition timing.
The model is basically composed of a frame which handles the engine, the transmission and the bodywork. The engine is a very simple pneumatic engine with one cylinder. This cylinder drives an axle that is connected to the inertia wheel axle by a gearing of 5:1. On the left side, there is the pneumatic valve that is controlled by a crank connected to the engine rotation through the adjustable ignition timing. On the other side, the axle of the inertia wheel protudes and drives a wheel and a 40-tooth gear which is connected to the fan on the top of the tractor.
The adjustable ignition timing is based on the differential principle. One side of the differential is connected to the engine rotation (input), the other side is connected to the valve rotation (output), the ring gear is locked by a worm gear on it. In nominal rotation, the input rotation crosses over the differential and the angular difference between the input and the output is null. In set up configuration, the user moves the worm gear, which drives slowly the ring gear, consequently the input is move back and the angular difference between the input and the output is not null. This device makes exactly what an electronic ignition point system makes on a car. It enables to do two things :
- Find easily the starting point of the engine
- In motion, find easily the best functioning which makes the running as smooth as possible
The steering is operated by the steering wheel near the seat, it drives an axle which crosses over the frame on the center and operates the steering with a worm gear on a 8-tooth gear. Then, a lever in rubber operates the steering thanks to its resiliency which also enables to have a good turning radius. To finish concerning the steering, the front axle is also equiped with a pendular suspension which is an improvement of my previous tractor.
The transmission is quite basic, the rotation of the engine is given to a rear axle thanks to many gearing. At the end of the transmission, I have placed a driving ring which a change over catch to make a basic clutch. Thanks to that, the engine can run and after switching the transmission move the tractor.
To finish, I have placed a suspended seat with a spring under it and the whole bonnet can be opened to see the engine running.
On this video, you can watch more presicely how the engine is built :
As usual I have created instrutions using photo sequence, and Alex an afol (afol1969) has made a brilliant work with it, with creating the pro building instructions ! Therefore I can propose you two version of the PDF instructions, one freely available based on picture, and one other made by Alex, for sale with pro-looked like. The bill of material is available as jpg here or on rebrickable.
You can buy the instructions with the following button for 10€.
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Air Pump (PDF – 2mo)
You can modify your switch and cylinder to enhance the performance, even if the tractor works fine with non modified pneumatic parts as they are smooth enought.
Here is the free available building instructions, as a photo sequence :