ENGR 3300: Gearbox Design Study


The following mechanism was designed to be coupled with a tool post attached to the z-axis of a farm robot. The design objectives of this project were to drive a hole saw and concentric augurer with a 40:1 reduction. The tool should also have a common bolt pattern with which it can attach to the main z-axis tool post.


The augurer and the hole saw are powered through two sets of transmission. The first is a simple 1:1 chain drive from the top mounted motor to the input shaft of the gearbox.  

The sprocket then connects to a keyed shaft that drives the first sun gear. The reduction happens in a two stage planetary gearbox. The first set of planetary gears has a 7:1 reduction where the 12 tooth sun gear drives 30 tooth planetary gears revolving inside a 72 tooth ring. A plate with an extruded shaft then transfers power to the second stage of the gearbox. Much like the first stage, the second stage is a planetary gearset with a 6:1 reduction comprised of a 12 tooth sun, three 24 tooth planets, and a 60 tooth ring gear.

The ABS gears are laser cut as and they are enclosed in an acrylic gearbox casing. The case itself is split into a top, mid and bottom parts with eight alignment pins on the inside to constrain the ring gears and six ½ -20 bolts on the outside sealing the case.

  The output of the gearbox then attaches to the the hole saw using a cotter pin. The shaft for the augurer then slides inside the the hole saw up to the output shaft and is also held in place by a cotter pin . This allows for the tools to be cleaned easily and/or replaced.