I am designing an RC car capable of achieving 20 mph and I am using a 3:1 gear ratio with my 10,000 rpm motors. In theory, it would work, but the universe hates me. I print the herringbone gears in PLA with no problems. Unfortunately, when I go to test them, the gear box catches fire and fuses parts worth 250 grams of filament into one, big pile of mush! Also, the noise it made was similar to the inside of a combustion engine! Does anybody have an idea of how to make a quiet, not flaming gearbox?
Print it in something with better heat resistance, PLA is not meant for things like this. I recommend a CF filament.
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You’re going to want to print those in something like PA (Polyamide - “Nylon”) if you want them to last.
Good luck!
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Heat is the result of friction. Reduce the fiction and there will be less heat produced.
What type of bearing are you using in your gearbox?
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I don’t have any bearings… How would they help?
Also, could I use Petg for the gears?
You can print them in any material you want. PETG might last a tiny bit longer than PLA, but don’t do it unless you really enjoy replacing gearboxes.
Bambu has a pretty good guide to help you select materials by properties. I’d look for high heat resistance and impact strength. Nylon is usually a good choice for plastic gears.
There are lot of gear design factors that affect noise. Try a search for “quiet gear design” in your favorite search engine for tips.
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Any alternatives to Nylon or Carbon fibre? I don’t have hardened steel and Nylon is too pricey.
Yes. Make lots of spare parts. 
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Bearings among other things reduce friction. Fiction creates heat.
Where would I put them?
Where the rotating parts interface with the fixed parts of your assembly.
Pictures of your gear assembly would be helpful.
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Could it have anything to do with your fuses? Louis Rossmann did a video about how a lot of fuses sold on amazon (and presumably other sources as well) are “fake”. They may not blow until they reach 5 or maybe 10 times their rated current. You may want to test yours.
But in any case, you can buy fire rated filament. It’s a thing. And some filament types are naturally fire retardant, meaning that they’ll self-extinguish when the ignition source (such as a blow torch) is removed.
Maker’s Muse did a video where he lit a range of different filament types on fire and observed how their burn characteristics differed. It’s easy enough to do this kind of test yourself with your own filaments. That way you aren’t merely trusting a datasheet.
But, yeah, it sounds like at the very least you should be using skateboard bearings, which would meet your requirement for cheap. There are a gazillion youtube videos covering this topic.
I don’t use fuses. Do you think I should with 12v 15 amps (at the most)?
Your fuse value should be the stall current of your motor. Normally this is listed in the motor specs but it seems that your Amazon motor does not have it listed.
You can measure your stall current with a multimeter.
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If I used bearings would I need to change the filament that the gears use?
12*15= 180 watts. So, that’s potentially a lot of heat going somewhere.
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I have heatsinks, but how could I dissipate heat with them if there is no way to mount parts on it?
It seems like nothing any of us are saying is registering in any way. I have to move on. Good luck!
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Is this enough @JonRaymond:
