[Jnadke]

This gearbox still doesn't address the issue of two motors having dissimilar torque characteristics.

Contrary to what Bill Beatty said, such a gearbox is excellent if you have two motors having identical torque but different free speeds.
To extend on what Bill said, the team was the Thunderchickens, 217.

When you think of gearboxes and motors, you can't think of movement. You have to think of the potential to do movement. In other words, you have to do think about forces acting within a gearbox. If you have a 300lb man, and a 100lb man, each leaning against eachother on a 45 degree angle, which will prevail? The obvious response is the 300lb man, because he has more force, or weight.

It's similar with motors. If you have a motor that outputs 500Nm of torque, and another motor that outputs 600Nm of torque. When such a gearbox encounters a position of stall (fighting against a stronger robot, for example), the extra 100Nm of torque will be wasted back-driving the opposing motor.

I'm not saying such a gearbox is bad. I'm just saying it's highly inefficient.

However, such a gearbox can be made to be extremely compact, if you think along the correct lines. You're focusing on a completely wrong topic here. The issue of two motors with dissimilar torque characteristics has already been solved by teams such as the Technokats by merely gearing down one motor.



EDIT: I didn't see/read the 2nd page.

I see you've added the gear-down of the drill motor since your initial design, that's a good start, but still you're focused on the wrong topic.

As for the people saying the differential is redundant. They way I see it, the differential is serving as a torque transfer mechanism. Most shifting gearboxes I've seen are large and bulky with a 3-stage gear mechanism. Using bevel gears as a way to combine the first and 2nd stages together, as this gearbox does, is a good start at creating a smaller and more efficient shifting gearbox.


Design Theory
One thing you could do is use different size bevel gears in the differential to combine the 4:1 geardown into the gearbox itself. I would mate the Chiaphua motor to the 1st stage using a shaft coupling. I would then, on the other side, mate the mate the Drill to the 1st stage using a 2:1 reduction. For the differential, I would use a 15 tooth and a 24 tooth (16 pitch) bevel gears to create a 1.6:1 difference between the two shafts. This would serve as the torque-transfer mechanism. I don't know if it's possible to match up different size bevel gears of the same pitch, but I'd assume it would be safe. The bad side is that you'd only be able to use 1 intermediate bevel gear instead of 2 as standard in a differential, so you'd have to support the shafts at the bevel gears so they maintain contact.

Basically, the gear closest to the chiaphua would be spinning at 5,500 RPM free-speed, and the gear closest to the drill motor would spin at 10,000 RPM free-speed. Match these gears up to the 2nd stage shaft normally as illustrated (using a 2:1 or more reduction I'd assume).


However, I'd need to note one major flaw in the gearbox design. In both cases, the intermediate bevel gear of the differential would have to be fixed (the gear that combines the two shafts), or no torque would be transferred. In which case the 1st stage gears would need to be spinning in opposite directions...
If you don't see where I'm going with this, your gears in your shifter would be spinning in opposite directions. Whenever you wanted to shift, your robot would suddenly stop, and move in the opposite direction...