One of our drive configurations has the entire robot supported by the toughboxes and axles extending from those tough boxes.
The only problem was we aren’t sure if the tough boxes can take all of that weight. If they can’t, then we would have to go ahead and use sprockets and gears.
Our robot is aimed at going under the tunnel, however, so sprockets and gears means space we don’t have. Hence direct connection is preferrable.
The tough boxes can take the weight. The question is, will the boxes put you over 120 lbs?
It would be a best practice to not cantilever those output shafts, instead you should support the output shaft at the far end. If you do that, the shaft will support several times the robot’s legal weight.
AndyMark has a long output shaft available as an upgrade option to the KoP toughbox unit that extends the output shaft by 3" or so.
We use that and support the outboard end of the shaft. It works great.
I don’t know how the toughbox would do on a direct drive with the cantilevered load… it’s not just the weight of the robot that you have to worry about, but also the tension in the chain… which, depending on the diameter of your sprockets, can become fairly significant. Add that to a bit of shock loading from a bit of looseness in the chain and… well… the toughbox can probably handle it, if your wheel and sprocket are mounted fairly close in, but I’ve never wanted to be the one to test that theory.
We have used the short shaft without any support. I did not want to do that but Andy said it would work fine. He was absolutely correct. You are only putting 1/4 of you weight on it. It should not be a problem. We are doing it again this year with Mecanum wheels.
If you mount the wheel next to the trans then the regular shaft if more that strong enough.