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Planetary hub reductions

Thursday 4 August 2011, by Karfo

When i saw Zblj’s planetary hub reductions on his TATRA i decided to make my own.

holding the grey part of turntable stationary, planet carrier as output directly connected to wheel and "sun" 8 tooth gear as input gearing ratio can be calculated from 1/(1+Na/Ns)= 1/(1+24/8)=1/4=0.25
so one rotation of the input rotates 1/4 on the output

[Na=24 (number of teeth in the stationary - grey part of turntable), Ns=8 (number of teeth of input "sun" gear)]

My design uses only 2 8 tooth gear in the carrier instead of Zblj’s 4 but it’s enough to prevent slipping gears (tire will slip on the rim).

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Forum posts

  • When you’re considering to go in the mud or avoid the mud with planetary gears, i can recommend you, to avoid it... :D Sand doesn’t do any good either (and even more if it’s windy).

    On the first international TT meeting we had at Keszthely (http://www.brickshelf.com/cgi-bin/gallery.cgi?f=477492 ; videos are currently under cutting), Zblj’s planetary gears got dirty inside, and made his whole drivetrain very resistant.
    The sand in the turntable inner side, (between the 2 sub-part), make a resistance force on a big radius, which cause a huge resistance on the axle in torque... Note, that this resistance means that your turntables are wearing out as fast possible (That’s where the power of the motors go...)

    Planetary gears are good, but never use when there’s a little chance to get dirty.

  • Like Hun_lac said, the dirt sure makes gears work hard, although they worked fine in initial tests. We will see how they work out for others.