Week TechVideo, 2009 #47 - An automatic gearbox (Ads must be paid...)

Long time ago we at TBs realized on a BS folder where Zblj (Jernej member of Kocke Klub, the Slovenian LUG) had photos from his Tatra 8x8 Trial Truck, taped with the URLs from some LEGO related websites (mostly well known ones).

It was with a big surprise and satisfaction that we saw also the TBs URL there.

Because ads have to be paid... , since then I had it also on my slow post queue and have been looking for something special from Jernej to highlight here.

Today I've decided for his attempt to build an LEGO automatic gearbox. It is not the first time we write here about automatic gearboxes [1], but this one uses a different principle. In fact it looks more like a CVT system (Continuous Variable Transmission), despite its narrow sensitive margin as it seems to switch quite fast.
It is a simple automatic gearbox design, using 2 differentials and a couple of gears.

Based on Jernej explanation here it goes how it functions, in simple words.
Differentials always slips to the easiest side. The left side has friction and the right doesn't. This means the power normally goes to the right. But when the load becomes higher than friction on left side, the power is sent to left side, where there is a higher gear ratio.
Total gear ratio varies between 1:1 and 5:1 (the ratio between the gears on the left side).

You will find it at this BS folder.


A good demonstration for the used principle, rests to know whether it can shows effective at up/down-shifts, into a real Technic vehicle or not.