FTC Custom Gearboxes?

Is there a good way to make custom gearboxes in FTC? For our robot we relied OTS gearboxes. But now that we’re in off-season, I have a couple of students who are interested in learning more about gearboxes and I’d like to have them build some kind of simple gearbox as a hands-on investigation.

In FRC in the past I’ve done something similar by laser-cutting 1/4" delrin gearbox plates and pressing in hex-bearings, but for this team we don’t have as powerful of a laser-cutter (maxes out at about 1/8") and FTC doesn’t seem to use that type of bearings, or 1/2" hex shaft. Ideally it’d be nice to use common FTC materials if possible for this project, so anything we order can be re-used down the line.

Has anyone done a project like this with FTC students? Or if you’ve done a different type of project for hands-on learning about gearboxes, I’d be interested to hear that too!

Fully custom gearboxes in FTC are pretty much unheard of, mostly because COTS gearboxes are plenty tough already. The UltraPlanetary system from Rev allows you to build custom-ish gearboxes that can teach about planetary gearboxes and are actually pretty good. Alternatively, you could make a fully FRC style gearbox with the GoBilda build system with their 8mm rex and bearings. It wouldn’t be practical but would be extremely fun and a great learning experience.

i have seen/designed quite a few, but mainly teams run ultraplanetaries or gobilda gearboxes with a single stage reduction to achieve the ratio they want.

Also, ftc teams used to use frc gears to make gearboxes, but with robots now being smaller to be lighter, this is less common

Thanks for the input. Sounds like maybe there’s not a great way to make it directly relevant to FTC, and I should just find something simple (maybe Lego gears or similar) that makes it easy to play around and see what’s happening.

On my team, I taught my teammates about gears and gear ratios with Legos and youtube videos. For actual Robot use we use the REV Ultra planetary motors and gearboxes. We like these so much because it’s not like typical FTC gearboxes. Typically, the Gobilda or Andymark gearboxes come in a few different standard ratios. The REV Ultraplanitarys come in 3:1, 4:1, and 5:1 stages, and you can mix and match up to 4 of them to get whatever ratio you like. They also have a really nice 90-degree output stage you can use with them.

The JVN calculator is also a really good tool for calculating what ratio you need with the weight or your mechanism as well as some other cool things.

JVN-DesignCalc.20170214.xlsx (843.8 KB)

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GoBilda has a variety of gears and pattern plates that make it easy to assemble gearboxes with all off the shelf parts. My teams use mostly gobilda parts at this point. You could also have your kids design something to be 3D printed. Herringbone gears are generally very effective with 3D prints. PLA should suffice as long as the parts are designed thick enough for the application.

There’s also an updated version made by team 77. It has more motors included although I don’t think it has FTC motors. You can add motors on the Data page if you find the data.
77 Design Calc - An edited JVN design calculator

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For low-load applications, you could probably 3D print a gearbox housing, or even the gears themselves in some cases.

We ran out of motors on our robot 2 years ago and wanted to add a spinner mechanism to get the ducks from the spinner station thing (whatever it was called). We looked at using Smart Servos in continuous mode but they were too slow to be useful, so we 3D printed a custom gearbox which ran 2 servos in a 1:4 ratio to increase the speed. Worked pretty good overall.

Also, while not a “gearbox” per say, we have also 3D printed geared grabber claws (think a scaled-up version of this) for FTC robots that have worked well.

The main thing to keep in mind for 3D printing gears is the size of the gear teeth (10dp vs 20dp vs 32dp, etc, larger is generally better) and the material you’re using. For larger gears (like 10dp) you can get away with PLA on stronger infill settings, for smaller gears (like the 32dp ones we had to use for the previously mentioned gearbox) we ended up printing them out of Onyx carbon fiber on our Markforge for strength (and the better accuracy of the Markforge).

If this was an FRC robot, I would usually make a gearbox by cutting out two pieces of 1/4" polycarbonate on our CNC router and sandwiching gears in them, but it sounds like you guys might not have the machining capability for that (and it’s not something that’s really needed for FTC anyways).

The Yellowjacket gear motors are good as they are, but there are a couple of things that interest me about doing custom gearing. 1) It’s all planetary gear stages, so maybe one could improve the efficiency by using spur gears. The motor power is more of a limitation in FTC, so there might be something there. However, it would add bulk to the design, and space is precious within an FTC robot. 2) The planetary motors stick out so far behind the motor that in some cases it would be easier to package a multistage gearbox as a spur gearbox or as a combination of belts and gears. That could make a custom gearbox appealing for a manipulator arm.