New design team member here -- are there any good tips and resources on how to design a gearbox?


#1

More specifically, gear math (ratios, spacing, shifting, etc.) and general design tips/resources on designing gearboxes? Thanks so much to the more senior members here in advance.


#2

I was you last year! These tips might be a bit repetitive from what you already know as I’m not sure what you don’t know. A tip i would recommend is to make sure that when you’re stacking pairs of gears, make sure the outer diameters of the gears don’t touch the shaft.

Drawing the sketches out in CAD where the circles and lines are constrained to each other help accomplish this.

if you can find access to a chart of a bunch of diameters for each PD and tooth number, that would be pretty useful. there are also formulas out there that you can use! (but charts are easier.) vexpro’s website already has the basic gear measurements. i even found a website last year that generated CAD files for custom gears as well as tell you the measurements! here’s the link https://www.rushgears.com/tech-tools/part-search/build-custom-gears

Also, even if asked to do a 204:1 ratio, a 210.92838484:1 ratio isn’t that different as the motor speeds vary anyways.

Another tip, unless you require your gearbox to be fully custom, stacking an 100:1 planetary gearbox combined with your own custom is pretty useful!

i think the math part is pretty standard, original RPM * distance per circumference * the teeth on the same shaft / the teeth it’s spinning = final speed


#3

When designing a gearbox sketch the pitch diameter (the location where a gear meshes with other gears) of all the gears and make mating gears pitch diameters tangent. Depending on machining tolerances you’ll need to throw in a little tolerance between gears but I can’t speak to those exact values. To determine the pitch diameter divide the number of teeth by the DP (usually 20 or 32).

This design tutorial from Team 610 walks you through the whole process. http://team610.com/portfolio_page/design-tutorials/

I’d also recommend the JVN design calculator for doing the speed math. Paper: JVN's Mechanical Design Calculator 2016

In general though I’d recommend using versaplanetaries for everything low torque that you can as they’re already designed and allow for quick iteration as you can easily swap out gears. Checkout the loading guide to make sure the VP can handle your given ratio. It won’t let me link it but it’s on the bottom of the VP Vex page under docs & downloads.


#4

Adam Heard goes through step-by-step how to design a gearbox in 973’s RAMP video series. This video shows how to design a whole WCD from scratch, but the gearbox part starts at 19:27. I highly suggest watching the whole video series if you have the time; it shows a lot of helpful tips and tricks to be a better designer/CADer.


#5

Not that you need to tell us, but if you’re going to design a gearbox, especially your first gearbox ever in the crunch of build season, have a good understanding of WHY you’re designing your own. Unless you’re trying to do something no COTS gearbox is going to achieve, you may be better putting off your first gearbox design to off season.