MPRT - Planetary Gear 90:1 ratio

prusaprinters

<p>This gear is made by me based on information found <a href="https://hackaday.io/project/164732-mprt-modified-planetary-robotics-transmission">here.</a></p><p>The gearbox uses a fixed ring and a output ring, allowing high speed reduction with a somewhat large sun gear.</p><p>Formula used to find gear ratio:</p><p><code><i>(1+fixedringteeth/sunteeth)/(1-fixedringteeth/outputringteeth)</i></code></p><p>In my case the numbers are the following:</p><p><code>fixedringteeth = 52 (must be divisible by 2 and number of planet gears)</code></p><p><code>outputringteeth = fixedringteeth - number of planet gears = 52 -2 = 50 (must be even number)</code><br><code>The gear pitch is adjusted using:</code><br><code>ring tooth pitch * (outputringteeth-number of planets)/outputringteeth</code><br><code>1 * (50-2)/50= 0.96</code><br>By adjusting the pitch, both gears will have the same inner and outer diameter with different gear count!</p><p><code>sungearteeth = 20 (must be divisible by 2 and number of planet gears)</code></p><p><code>planetgearteeth=(fixedringteeth-sungearteeth)/2 = (52-20)/2 = 16&nbsp;</code></p><p>&nbsp;</p><p>This gearbox ratio using the first formula gives:</p><p><code>(1+52/20)/(1-52/50) = 90</code></p><p>By holding the fixed ring, and turning it 90°, the output will rotate only 1°</p><p>Other combinations are possible, just use excel and calculate whatever gear you find suits your needs best. Depending on your settings you might need to scale up the sun and planet gears to get a tight fit by 1-4%.</p><p>The bearing I used is 608ZZ</p><p>Instead of printing the handle you can use a 6mm Hex bit or tool. You can modify the fixed ring and sun gear to have an additional bearing if you want to mount to a NEMA motor or similar.</p>