Differential Planetary Gearbox 43.3:1 No Hardware, Less Backlash

Summary Updates! Uploaded the Rotating Base http://www.thingiverse.com/thing:2166517 3/10/17- Youtube Video! https://www.youtube.com/watch?v=RcUrgxrOqVo&feature=youtu.be 2/27/17- I designed a one piece sun gear for this, one version with a large drive gear on it and one version with a 5mm D shaft hole, the one piece sun gear is compatible with the 3 & 4 module planet gears. if your using the 4th module you may choose to use the #2 sun gear in module 4 in conjunction with this. Using the one piece sun is a good upgrade for this as it cuts down on backlash. I designed this gearbox for my Modular Robot Arm Project, check it out! : Origional model http://www.thingiverse.com/thing:2105057 EZ Print model https://www.thingiverse.com/thing:2153317 Mounting Base For Testing http://www.thingiverse.com/thing:2154052 Use the origional model for attachment to the mounting base, the EZ print version has no attachment method for that. The EZ print model is better used between two joints. Both models are 100% compatible with this gearbox and each other This gearbox is an update to my previous gearbox, the main differences being that this one has a much lower backlash setting (.1mm VS .25), uses a different helix angle, has more external grip teeth, the Rings Gears are not as wide, and has a optional extra module. Assembly ------------------------------------------------------------------------------------ Align the planet gears in order as shown in the main picture, insert a sun gear, Snap Ring Gear #1 on, Inset all sun Gears, snap the other 2 or 3 ring gears on, also, you will need to close the gap in the rings before you spin this gearset or else it could skip teeth and get out of alignment, for this i have included the ring closures, that fits over all the rings For any instructions i may have missed, please refer to this : http://www.thingiverse.com/thing:2081324, this gearbox is very similar in concept. How it works ------------------------------------------------------------------------------------------ When you rotate Sun Gear #1 (The sun Gear with the D-Shaft hole) The Planet gears orbit that gear causing Sun Gear #3 to rotate at the exact same speed as Sun Gear #1 Now, When the Planet Gears make a full 360 Degree rotation around the Sun Gears, Ring Gear #2 ( and the Optional Ring Gear #4) will move 27.7 Degrees, ( 2 Teeth) The other important thing to realize here is that Ring Gears #1 & #3 will be at the same potential and Ring Gears #2 & (Optional #4) will be at the same potential The use of Ring Gear #4 and the 4 Module Planet Gears is optional and used to increase the amount of torque this gearbox can transfer, as well as to decrease the amount of (radial?) load on each gear, think of it like a door hinge. When you use the 4th module you should re-use Sun Gear #2 to space out the planet gears within Module #4 ////----------////----------How to Design your own--------////----------////----------////---------- If you would like to design a gearbox like this to integrate into your own project, just follow these somewhat complicated and poorly written instructions. You will need two planetary gear sets, the closer the number of teeth, the higher the output gear ratio will be. The following design constraints are very important: But First, design tips: The more planets, the harder it is to meet all the constraints. 2: using gears with lots of teeth can achieve very high gear ratios(500:1+), and higher ratios than i have designed have been achieved by others, such as Emmet. Gears with a lower pressure angle have much less friction, and last longer, but aren't as strong. I am experimenting with newer designs with 20 deg pressure angle and they're very promising. You will need to study the gear tooth combinations that work properly in a planetary gearset, keep in mind that not every combination of gears will fit together, and not every combination that fits together will allow for evenly spaced planets (and that IS necessary), to find gear combinations that fit these two design requirements, use these two equations. For Figuring Gear Combinations that fit together: Teeth_Sun + (Teeth_Planets*2) = Teeth_Ring_Gear For figuring if the planets (pinions) can perfectly evenly spaced: (No_of_teeth_sun + No_of_teeth_Ring) / Number_of_pinions has to be integer. Keep in mind that those two equations will not prevent you from making planet gears that overlap, heres a quick tool for that: http://www.thecatalystis.com/gears/ Once you have decided on a number of planets and your two planetary gear combinations that you would like to use you need to model the gears, You will need to go off into your CAD program. When modeling the gears the most important design constraint is keeping the planets from each gearset at the same center to center distance. Use the following equation to align the planets from the two planetary gearsets with one another: Planetary Gearset #1 (Sun Gear Pitch Diamerer + Planet Gear Pitch Diameter) Must be equal to: Planetary Gearset #2 (Sun Gear Pitch Diamerer + Planet Gear Pitch Diameter) you can set the pitch Diameters equal in your cad program by adjusting the module(the number of teeth per mm) of one planetary gearset in contrast to the other. FYI the pitch diameter of a gear is the size of the circle that is made when it meshes with another gear. I.E. if the gear was a cylinder, rolling against another cylinder.