Been looking around to find some good articles or links for some tutorials on gearboxes and how to choose the best ratios for various mechanisms (i.e. drivetrain). Anyone know of anything that could help me out?
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It’s a tutorial for inventor but it’s easy to follow with other CAD softwares as well.
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Well for choosing ratios, there are spreadsheet calculators you can use. My personal favorite is AMB Design Spreadsheet (search that on CD). It lets you configure everything about a gearbox from motors, ratio, stages etc and tells you what the resulting speeds and torque will be.
Here’s the spreadsheet: AMB Design Spreadsheet v4
Also has other things you may find useful like pneumatic linkages
Also what I found is that if you look at what REV, AM, Vex, WCP sell gearbox wise, well the thing is everything they make has a specific purpose for FIRST so what helped me is looking at that and understanding the purpose and then thinking about where it can be used. A lot of them also have nice descriptions that help a lot.
Also keep in mind that planetaries have load limits and Vex and AM both have data sheets that list maximum ratios depending on motor input so be sure to check your ratio fits
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ok thanks for that info guys but this has lead to a second question, are there any real differences with using custom gearboxes vs. a premade one like the toughbox mini’s? Our team plans on hopefully using the new falcon 500s but are debating on whether we push for custom ones or buy the versaplanetarys.
The primary benefit of using custom gearboxes is that you have total control over the design. This includes mounting, integration, overall sizing, motor count and type, encoder, shifting, number of stages, and package shape. You can typically always find something “good enough” in this day and age of in this day and age of FRC, but they’ll never match the degree of freedom you get from custom gearboxes. Custom generally is a bit cheaper, as you save the markup and secondary handling/design cost and instead take up that work yourself.
On the other hand, COTS gearboxes have a number of conveniences. Planetaries have an excellent width/height profile, and make swapping ratios relatively easy. Most other COTS gearboxes are nice because they save you from machining. Some teams use these for the drivetrain to save themselves time on machining early on. In general, if you’re lacking in design and machining resources, use COTS.
In terms of performance, a COTS gearbox and custom gearbox will work just as well when used.
If you have easy access to a CNC mill, and a decent CAD team, I think you should strongly consider going custom for most of your gearboxes. If not, look more into using COTS gearboxes.
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I put some mini-classes I taught a few years ago up - the first drivetrain presentation covers selecting gear ratio and wheel sizes.
Then, there’s this comprehensive guide for new roboteers from last year! It’ll likely answer nine of your next ten questions:
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Bottom line - if you haven’t built a custom gearbox before, I recommend you do one in the offseason first. These days, there are so many COTS gearbox options that some teams with the capability opt for COTS to save time during competition season for things like tuning, auto programming, and drive practice. That said, VPs are not an optimal choice for drive trains, at least not for one with a direct drive axle (no belt or chain).
You don’t need a CNC Mill. A waterjet, CNC Router, or a laser cutter if you choose to use plastics. Look for companies near by that would be willing to help you.
And I’ve had people who know what they’re doing work them on manual mills (usually ones with a digital readout). CNC is hardly a requirement to go custom, but competent machining is.
Repeating this for emphasis. Whether from AndyMark or VEX or WCP (I don’t think REV has any Falcon-500-capable gearboxes), there is very likely a gearbox that will meet your requirements straight away. We use RedLines and 57 Sports at 20:1 and 100:1 for just this purpose: odds are that shafts spinning at 1000 or 200 RPM (…ish) are what we will need somewhere in our robot. Then a Two Motor Sport if we need about 6k RPM, regardless of whether we need a second motor. From there, we can usually tune it with a belt or chain run as needed.
I can highly recommend the JVN Calculator. There are several YouTube videos on how to use it.
Before choosing to make a custom gearbox, you should consider your team’s ability to get parts manufactured quickly in sufficient quantities and with sufficient accuracy, regardless of the manufacturing equipment you have access to. Gearboxes tend to be critical components that have great influence over the success of the mechanisms they are used in. Being 90 or 95% done rounds down to zero when you place your robot on the competition field.
If you are concerned about your abilities to finish on time, you can design your mechanisms to use a COTS gearbox and allow some extra space so you can also use a custom gearbox. That way, if your custom gearbox doesn’t work out, you have a Plan B.
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If your a noob to FRC I would recommend tough box mini on your drive train with the stock gear ratio. Then pick up some Versa Planetaries (VPs) before kickoff and learn how to assemble them for your other mechanisms. A 45:1 with a 775pro motor has been used more than once on our robots. So a 7:1 stage and a 5:1 stage. You have to read the VP manual to not get bit by the details. It is a lot easier to do this without the time pressures of build season.
57 Sports are a solid alternative to the Versaplanetary if you need more strength than the Versaplanetary allows for. Andymark also has CIM and Falcon variants, with nice tables that tell you if the maximum torque exceeds the load rating of the gearbox.
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Either is a 500% valid option for handling smaller motors (BaneBots 550, NEO 550, 775pro, RedLine), and there’s a lot there for the CIM-class motors (CIM, Mini CIM, NEO, Falcon 500).
VersaPlanetary gearboxes have the advantage in configurability, and there are more trick plays like the ratchet, encoder, 90-degree, and 180-degree features.
Sport gearboxes are cheaper for a given gear ratio ($78 vs. $90 for a 20:1 last I looked), have higher load ratings, and (aside from the 4:1) there’s a consistent mounting pattern regardless of ratio. VEX and REV now have hex bore encoders depending on whose motor controllers you prefer, AndyMark has the LJ Bevel Box with similar functionality to VEX’s 90-degree kit (but larger and more expensive), and ratchet wrenches are a common solution when those are needed.
You’ll probably want to pick one ecosystem or the other.
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