Gears rant

here is picture for you

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Uh wat
I have a gear ratio lifting an entire dr4b and it never had any issues. I was running 1:25 and never had anything explode

i have more pictures.

IMG_20191221_204615 IMG_20191221_204549 IMG_20191221_204439 IMG_20191221_204350

I have a bit of input, just from what I’ve experienced and what I can tell from looking at your images.

1:9 gearboxes going 1:3 - 1:3 are very difficult to make, the amount of torque that the final 36T gear is subject to is … simply put, quite a lot. There’s a few things that you’ll want to keep in mind; just from what I can see.

Make ABSOLUTELY SURE that you’re bearings are all perfect - some bearings aren’t built perfectly, and will shift side-to-side. Even being half a millimeter off will cause gears to snap teeth, especially with this amount of torque.

Second thing. Axles in vex will deflect. You might not be able to see it, but again, any deflection you get in the axle is going to cause gears to move away from each other, which will cause gears to snap.

In my time doing VEX, we’ve put a lot of gears under a lot of stress, we’ve put a lot of torque through a lot of gears, and we’ve never had any issues when we watched for those few things. It’s entirely possible for your entire gearbox to look sound structurally, but have a tiny mistake which compounds into many gears snapping.


So basically, if it is very hard for the gears to skip teeth, the less chance that the gears will break?

Yep. If they skip, that means the force is regularly being placed entirely on the tips of the teeth.


Alright, thanks. Quick follow up, are there other ways to get the gears to mesh together better? I’ve tried zip ties.

I would stay away from zip ties because of the friction it causes on the system. Generally if something is skipping it means the shaft is bending out of place (assuming the gears are lined up and aren’t diagonal). I try to add support structure as close to the skipping gears as possible. Paired with the bearings, it’ll minimize the amount the shaft can bend out of place.

An idea you might want to try is getting a slow motion video of the gears skipping to identify exactly what is moving out of place.


My tiller is 1:21, and we had the same issue, switching to high strength shafts really helps, it does 12 with no problem

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your axles are a lot longer than they need to be, which gives them more room to flex and skip and break gears. try using screw joints on your gears, or high strength shafts.

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Keep distances between bearings short - ideally you have bearing washer gear washer bearing, with no need for spacers or dead space.

Make sure you’re using bearings that are totally solid - there are differences in bearings, pick some that are solid, have new teeth, will lock into place, and tighten them down to make absoblutely sure that they are not moving. Make sure the holes on the bearing are round, and not excessively large.

Make absolutely sure that everything is as parallel as can be.


Another thing that I don’t believe has been mentioned yet is that when building a gearbox you should generally make it so that the mechanical stop breaks/the motor overheats before gears start to skip. If the gears start skipping when whatever you’re powering reaches a mechanical limit, most likely your gearbox isn’t built well enough.


Yeah make the gearbox so that the motor can no longer turn when the load gets too high.

Try using screw joints instead for the final gear in the geartrain (you can shift screws around within the holes to mesh less or more, and screws are far more rigid than axles, which will regularly just bend in the gearbox you posted pictures of. I would also not be surprised if they are twisting prior to the lockbars)

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Curious if excessive mesh can cause metal teeth to climb up (or otherwise shred) the plastic teeth after compressing them, and also did the friction (or internal flex) get the plastic gears hot?

backlash tech discussion

Plus, zipties stretch (and maybe change tension with temperature?)

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I wasn’t suggesting gear compression. The gears are not excessively meshing since they were designed to function a certain distance apart (which is kind of hard to screw up unless you drill holes into your metal).

using zipties works on the principle of compression, regardless of their tension. They could cause excess mesh (though I doubt it) and will still cause unnecessary friction as a result of compressing shafts together.