Quote:
Originally Posted by 1683cadder
Is there a list of formulas? I know there are calculators, but I want to know formulas. I wouldn't make custom gears for FIRST but for BEST we sometimes make gears with jigsaws.
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Ahh, geartrain formulas. A really nice resource that I use is my college-level engineering textbook on Machine Design. To understand the WHY of those formulas without calculus is roughly equivalent to being very lost without a map of the area. To use them without calculus, OTOH, is actually possible.
The good news is that if you're just calculating a gearbox ratio, you just need to know the intermediate ratios. Let's take a single-speed gearbox--oh, let's grab a pair of AM Stackerboxes just for grins. As simple as it gets... one input gear, one output gear. 3.57:1 ratio (from here on out expressed as 3.57/1). Take two in series, and you get (3.57/1) * (3.57/1)= 12.7449/1.
Now, that formula (
ratio 1*ratio 2=gearbox ratio) is expandable to any number of intermediate stages.
What that ratio does: It multiplies torque at the expense of a divided speed. Using the stacked Stackerboxes with a single CIM, running unloaded, you end up with 5500 RPM/12.7449=431.5 RPM at the output--but your torque went up by the same factor. If you had a 1:X gearbox, where X>1, it would have a reverse effect, speeding up the motor at the expense of torque.
Most folks who design custom FRC gearboxes will space the holes using the gears' pitch diameter (where they mesh with other gears)--take the sum of the pitch radii, add about 0.003", and usually that works.
I could go into gear design itself, but that's pretty ugly, or gets that way after a little while. Shaft design might be more helpful, but that's one where I'd just use COTS shafts rather than deal with squares inside of square roots inside a cube root.
Going on to some of your other questions:
Sure, you can test the gearbox in CAD. Do I know exactly how? No, due to not playing around with the motion constraints and other similar stuff, but I'm willing to bet there's a tutorial or someone can help you.
Can you use it next season if you guys publish the CAD? I'll let you know on January 4, 2014, but under the 2013 rules, that would be a Gray Area governed by R16. The CAD would be publicly available, but the gearbox would not be. Whether CAD counts the same as software is up for debate. But if you were to make changes to the gearbox design, and build a new one, you'd be quite legal. (My personal opinion, not valid at inspection, is that it would not be legal without the modifications--second example in the blue box.)