Custom Gearbox is very loud

[Cothron Theiss]

Originally Posted by Tottanka

So we just build our first ever custom gearbox, and it's one of the "opened" once. As in, you can see the gears and all, and when testing it we feel like it's very very loud compared to anything wev'e had before.
Now, all our previous gearboxes were enclosed once, like the ballshifter for example.

So what we want to know, if that loud noise is just how it is supposed to sound like with an opened gearbox, or is that means that something's wrong.

Thanks!

Going of off the advice already offered in this thread, the first thing to do is check the actual center distances between your gears. The other thing is to make sure your shafts are perfectly parallel. Gears can take a few thou of play in the center distances without too much issue. They can not take a few thou of axial misalignment without protesting.
If your center distances are at exact or anything below that, you can add a .003 to .005 to loosen the meshes up a little. If this still doesn't fix it, or your actual center distances already had a bit of space, you can try the methods GeeTwo and Type suggested, and you can try wearing the gears in by running the gearbox with no load. I've heard the run times for this need to be anywhere from 30 minutes to an hour. If you take this route, remember to clean your gears after the run-in period. Wipe all the grease off, use a bit of acetone to really clean the teeth, and then re-grease. Hopefully, one of those things fixes your problem.

EDIT - All the dimensions I mentioned are in inches.

[Tottanka]

Thanks everyone.
I'm leaning towards trying the wear down methods just to learn more about it and see how it goes. If that won't go we'll probably remake the whole thing with the suggested distance adjustments.

[s_forbes]

Originally Posted by Tottanka

Thanks everyone.
I'm leaning towards trying the wear down methods just to learn more about it and see how it goes. If that won't go we'll probably remake the whole thing with the suggested distance adjustments.

If I had a gearbox constructed like the one that you have, I would do the same thing. Good experiment to run! If you can, post a picture of your setup and findings if you do it.

I'll echo what everyone else said: we add 0.003" to our center-to-center spacing between gears. Using hex shafts and gears with hex bores, it's really hard to keep everything within a tight tolerance. The extra spacing keeps gears from binding.

[nathannfm]

How are you locating the CIMs? Since you say it seems that that is where the sound is coming from it is possible that the pinion to first gear spacing is the problem and all the others are fine. I would recommend loosening the CIM mounting bolts, then pulling the CIM away from the other gear (increasing the C-C distance by a hair) while someone else tightens the CIM mounting bolts back.

[Sperkowsky]

Are the cim motors square to the gearbox? If the cims aren't mounted securely they can sag and cause quite a bit of misalignment. Have someone run the gearbox while lifting the motors up to check.

[dirtbikerxz]

Can you post a video of the gearbox running? Your definition of loud may be different from everyone else's definition of loud.

[Chris is me]

Originally Posted by nathannfm

How are you locating the CIMs? Since you say it seems that that is where the sound is coming from it is possible that the pinion to first gear spacing is the problem and all the others are fine. I would recommend loosening the CIM mounting bolts, then pulling the CIM away from the other gear (increasing the C-C distance by a hair) while someone else tightens the CIM mounting bolts back.

In future designs, *always* use the CIM boss to locate the CIM for gear spacing. This will get you a more accurate and robust result than using the bolt holes.

[Tottanka]

Originally Posted by dirtbikerxz

Can you post a video of the gearbox running? Your definition of loud may be different from everyone else's definition of loud.

Will do. Sometime tomorrow.

[cbale2000]

Originally Posted by Chris is me

...the CIM boss...

The what now?

[Chris is me]

Originally Posted by cbale2000

The what now?

A boss is a protruding mechanical feature, usually used for locating pieces together. The CIM has a .75" diameter boss concentric with the output shaft, which makes for much more accurate locating than simply using the bolt holes. The tradeoff is that a 14T pinion can't fit through a .75 diameter hole, so you should use a 12T or 11T pinion.

[Tottanka]

So here are some of the results:

Running the gear for 1 hour only helped slightly, still too noisy.
It seems that when the CIM body is moved a little the noise is far less loud, this drew us to the conclusion that the distances have to change, and we are now remaking the gears with the 0.003'' addition to the distances of the gears.
Will keep posting with results.

[Chris is me]

Originally Posted by Tottanka

Running the gear for 1 hour only helped slightly, still too noisy.
It seems that when the CIM body is moved a little the noise is far less loud, this drew us to the conclusion that the distances have to change, and we are now remaking the gears with the 0.003'' addition to the distances of the gears.
Will keep posting with results.

Sounds like that is probably the source of your problem. Honestly, the less you are able to move that CIM the better. If you are using 14T pinions, don't. Use 12T pinions so your center hole can be exactly .750" and your CIM will pilot correctly and you won't have this issue to worry about.

[Tottanka]

Originally Posted by Chris is me

Sounds like that is probably the source of your problem. Honestly, the less you are able to move that CIM the better. If you are using 14T pinions, don't. Use 12T pinions so your center hole can be exactly .750" and your CIM will pilot correctly and you won't have this issue to worry about.

Will do. Thanks.

[Sparky Jell-0]

It shouldn't have that significant of a increase in volume just because it is open box. do you have lubrication on the gears, that usually quiets it down well. also re check your math on the spacing of the gears to make sure they are meshing well and aren't too tight. that should fix the problem.

[JesseK]

@Tottanka -

Inspect the CIM pinion gears themselves. It doesn't matter who manufactured them. In the past, we have received about 1 in 10 pinions as just completely unusable. In one case the gear teeth were complete triangles rather than the usual tooth profile. In another case the gear teeth were all 'skewed' clockwise. We usually keep them to make sure students understand the importance of verifying purchases before use, so I'll try to remember to get some pictures sometime before the season hits.