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| Crane Crawler Base | ||
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The crawler base is an incredibly strong structure. Each side has a double row of Technic crawler treads and it uses eight 40-toothed gears total. Each track is motorized by one 4.5 volt Technic motor. | |
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The crawler base must withstand the weight of the entire crane and the load. The most extreme loading occurs when the crane is performing a heavy lift and the back of the crane tips up. That means that the entire weight of the crane (and the load) is supported by the front gears.
Even though in real life this shouldn't happen, the structure must be designed to handle this condition. Should a real crane be overloaded, it will slowly start to tip over. I've seen this happen in the offshore industry (i.e. crawler crane on a barge deck) and the operator has time to release the load before the crane tips over. |
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With the purchase of many Dacta service packs of crawler treads, I was able to construct the large crawlers. Before I bought them, I didn't have enough and that's why
Crane 93
(my first attempt at a large crane in 1993) was built on rollers and not crawler treads.
In fact, the purchase of the crawler treads really started this whole thing off. They were the "key" element in the model. |
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There are no rollers or gears along the bottom track between the end 40-toothed gears. I did this for two reasons: 1) no gear or roller would fit easily and 2) in the extreme loading condition, only the front gears support the entire structure so middle rollers are useless. This is okay only if the crane is rolled on hard, level surfaces. When placed on carpet or uneven ground the bottom tracks scrape against the crawler frame. | |
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Ah, yes. ANOTHER view of the crawlers. | |
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Here are the "guts" of the crawlers. In each side there is one 4.5 volt motor and a gear train. The reduction ration is 1:1080. I know that's incredebly low and yes, gearing that low results in gear-breaking stresses. I broke a few 24-toothed gears before strengthening some parts.
The 24-toothed gear driven by the worm gear was the one that broke. I put 4 additional axles to help distribute the torque. This solution was satisfactory and I haven't broken another gear yet. The image was created with MLCAD. See www.ldraw.org for info on the program.
LDRAW file (DAT) of this model:
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The motor and first few gear sets (prior to the worm gear) were built into a removable module. If you take the crawler tracks off and pull out a few 3L black pins, the module will slip out.
I did this so that I could adjust the gear ratio later if need be. However, the 1:1080 ratio worked out fine as the crane moves just slow enough. It seemed to be a good speed considering how slow real crawler cranes move. |
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