Hi all, I’m looking at designing a custom gearbox just to try on the off-season. Any tips? Any specific numbers to keep in mind for things like the distance between two shafts for a 74 tooth interaction (is that the right word? the spacing between the centers of like a 24 and 50 tooth meshing) and a 64 tooth interaction? Tips for designing the plates to be weight reduced similar to the nice style that WCP has? Thanks.
973 RAMP videos are pretty good for exactly what you’re describing.
What you’d need to figure out your distances is something called pitch diameter. The pitch diameter is an imaginary circle around the gear. When you mesh two gears together properly, the pitch diameters of each gear would be perfectly tangent (thus the PD is slightly smaller than the OD of the teeth on the gear).
The formula for pitch diameter is PD=N/DP where N is the number of teeth and DP is the “diametral pitch”, which is the number of teeth per inch of Pitch Diameter. Usually in FRC this number is 20 but others are available as well. For example you can see here that all of Vex Pro’s gears are 20dp.
Now to put it all together. Once you solve for your pitch diameter of one of your gears, cut it in half to get the radius. Do the same for your other gear that you’d like to mesh with. Add the two radii and you have your distance! Crude MS paint visualization.
Finally, usually we add a little extra wiggle room. I use 0.003" successfully but I’ve also seen 0.002" recommended. Maybe someone with more knowhow can weigh in on which is better and why or if it really matters at all.
So in your example, your gear center to center distance would be (74/20/2)+(64/20/2)+0.003
Here’s a time lapse I made awhile back of modeling a gearbox just for fun (mostly to try modeling a style of drive I wasn’t familiar with at the time). Let me know if you’d like to know anything else.
Other tips:
You can retain the shafts of the gearbox by using hex shafts but turning down the ends and using round bearings. For example, half inch hex turned down to half inch round on the ends and ran through half inch round bearings. Place the bearings with the flanges on the inside face of the gearbox so they can’t fall out either.
Consider how you would mount an encoder if that’s something you’d want to think about
Thank you so much this is exactly what I was looking for!