pic: Top Down Gearbox View

[RMS11]

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[=Martin=Taylor=]

The face of those gears looks awfully narrow. You might get away with .25" face for the first gears, but the output gears really ought to be .375" or greater (especially for a direct drive).

At least give the gears thicker hubs.

[RMS11]

Originally Posted by Hachiban VIII

The face of those gears looks awfully narrow. You might get away with .25" face for the first gears, but the output gears really ought to be .375" or greater (especially for a direct drive).

At least give the gears thicker hubs.

Why? I was thinking that since since there are 3 reductions that each gear only takes 1/3 of the force.

[Cory]

Originally Posted by RMS11

Why? I was thinking that since since there are 3 reductions that each gear only takes 1/3 of the force.

your thinking is a bit backwards.

The initial reduction will take the least amount of force, as there is the least amount of torque.

As you subsequently gear your transmission down, the torque of the motor becomes multiplied by the gear ratio of each stage of gearing.

[RMS11]

Originally Posted by Cory

your thinking is a bit backwards.

The initial reduction will take the least amount of force, as there is the least amount of torque.

As you subsequently gear your transmission down, the torque of the motor becomes multiplied by the gear ratio of each stage of gearing.

So I should be more worried about gears slipping or shearing because of the thickness?

[vivek16]

Originally Posted by RMS11

So I should be more worried about gears slipping or shearing because of the thickness?

err, shearing, bending out to the side, and then grinding lots. Slipping is the least of your worries.

Each gear will take the full force because gears in gearboxes mesh in a series, not parallel.

I would definitely make them thicker. They are waay too thin.

What pitch are those by the way? I suggest not using anything too small. 20 dp is a good size, its what AM uses. If you need any help, my AIM's in my profile.

good luck, Vivek

EDIT: cory's absolutely right. you still don't want anything too thin. better too strong than too weak.

[tennispro9911]

My advice is anytime your intuition tells you something, double check it with physics. That's something that's served me well is to both trust my gut, but make sure my gut is correct, and make sure someone else confirms that if I am designing something critical to my robot's success such as a gearbox. Also, don't view criticism as negative, but rather that all of the people on CD want to make sure that come competition, everyone has a working robot.

[Cory]

Originally Posted by RMS11

So I should be more worried about gears slipping or shearing because of the thickness?

You'd probably run into problems with teeth shearing off.

3/8" face width 20 DP is generally the defacto gear type for FRC drivetrains.

Depending on the type of load you'll be seeing, you can increase DP or reduce face width in earlier stages. In output stages you probably don't want to go less than 3/8" face width and 20 DP.

Again, there is math that will verify these rough guesses, but that's a bit more complicated.

[RMS11]

Originally Posted by Cory

You'd probably run into problems with teeth shearing off.

3/8" face width 20 DP is generally the defacto gear type for FRC drivetrains.

Depending on the type of load you'll be seeing, you can increase DP or reduce face width in earlier stages. In output stages you probably don't want to go less than 3/8" face width and 20 DP.

Again, there is math that will verify these rough guesses, but that's a bit more complicated.

Is there a place you would recommend gears with 3/8 face and 20 pitch? We normally buy from wm berg because of their great selection of gears but they only come 1/8 thick. We could though double them up, but that gets to be like 40 or for 3/8 60 dollars per gear... Thanks

[vivek16]

Originally Posted by RMS11

Is there a place you would recommend gears with 3/8 face and 20 pitch? We normally buy from wm berg because of their great selection of gears but they only come 1/8 thick. We could though double them up, but that gets to be like 40 or for 3/8 60 dollars per gear... Thanks

www.andymark.biz

They even come prebroached.

-Vivek

[M. Mellott]

You can get them from McMasterCarr, or go to one of the primary manufacturers at Martin Sprocket & Gear, Inc.

[Triple B]

233 has always used 32 pitch for the first stage of our gearboxes. We have even used 1/8" face width with no problems. The second and if necessary third stage is usually 24 pitch. We have used 20 pitch gears if we cant find the ratio we need in 24 pitch. All our gears use the 20 degree pressure angle.
mike d