GEM500 (am-0401)--adding stages?

Hey everyone,

The AM website talks about the GEM 500 (link)]( , saying “Theoretically, an infinite amount of stages could be stacked on this gearbox.” But they only sell it at 3, and they only give stats up to 4. We’re considering stacking 5… One of our mentors expressed concern about the “gears becoming dust.” Has anyone stacked 5? Do they know if it works, or what the efficiency is? (we assumed 50%)


You want 5-stages? 665.78:1 is madness! What operation requires that large of a reduction? The gears shouldn’t slip (referring to the ‘dust’ statement) so that should not be a concern; unless he is talking about a gear on the output shaft, as that would require high tensile strength due to the insane output torque…

We would need to know more details about your application in order to determine if gear strength would be an issue. When in doubt, using a planetary for the first few stages and finishing with a few spur or chain reductions is not a bad idea.

We’re looking at about 400 ft-lb of torque attached to the output.

What is attaching to the output shaft of the GEM500? Is it cantilevered? Is this being used as a winch mechanism? You will only get 8 rpm if you are using a standard CIM motor with 5 stages.

Yes, I realize it will be very slow. We spent a lot of time working on the math. It will be attached to an arm that is about a foot long, but, no, it is not part of a winch mechanism. The arm needs to move a relatively short distance, against a lot of resistance.

I’m not concerned about the speed or torque, we’ve found those (with JVN, amongst other things.) I want to know if anyone’s done it and what they found.

Then I assume your initial question is subjective to the mechanism you design to provide the slow/high tourqe operation you are asking for? The lack of information provided is insufficient to properly answer your question (beyond the broad question of asking if anyone has utilized five stages at once).

Sorry if I’m misinterpreting this.

I’m assuming you’re attaching the arm directly to the output? If you use a sprocket and chain for the final reduction instead of an additional stage of gearbox, it reduces the force the gearbox sees by an order of magnitude and allows you to make adjustments to your final arm speed if you find it’s too fast or slow.

In all honesty, a lot of this was to reassure my mentor that the 4140 case hardened steel gears would not turn to dust. But the rest was to see if anyone had done it, and what they found. Thanks for your help.

Also, we’ll look at the chain idea, but I’m not sure it will work in the space we have. But thank you!

They will not shear unless the counter-shock force exceeds the tensile strength of the gears (which the gearbox mount is more likely to fail first).
In standard operation they will be more than okay.

Cave Johnson here,
We asked this question because we want to make sure our drivetrain does not fail in the middle of a match.

we are building something like this:

Hey guys, is there a way to delete posts?

I tried this design back in 2009, but we ran into a few problems with the balance. I would suggest keeping the battery in the back so it isn’t as front heavy.

Just thought I would through this out. There are no other output shaft options available for the GEM gearbox, except for the one that it comes with. Should you direct drive off a 5-stage GEM variant, you are likely to produce a torque load that exceeds the material strength of the shaft itself. You could of course machine your own solution, but have fun with that!

I ran a 5 stage GEM gearbox a week ago to demonstrate an idea. It maxed out at 178 pounds of lifting, direct driving off of the 666:1 GEM 5 stage gear box and an arm length of 9 inches. Fact: I tested to failure. Fact: your robot probably will not weight 178 pounds (see FRC manual!!). But how long is the arm length and what kind of moment are you putting on that shaft?

You would probably be way better off running a 3 or 4 stage variant of the GEM gearbox, then have further reductions via either a worm gearbox or some chain and sprocket reductions. just my .02.