pic: Team 2220 Blue Twilight Octocanum Offseason Project

[Jeffy]

Originally Posted by sentientfungus

The way we have it geared currently, by my calculations (using a 1:9.52 gearbox like the the VexPro double reduction), we would be running at ~12 fps adjusted on the mecanums and ~8 fps adjusted on the tractions (using the JVN 2012 design calculator).

To me, those both sound like rather reasonable speeds. There's also that we have a maximum sprocket size on the 4" wheel (which I believe is something like 44t sprocket). Running that reduction would bring us down to ~6 fps adjusted speed. That's something we might consider if we were to run this in a competition, but probably won't deal with on the prototype, at least initially (because of the aforementioned large amount of 32t sprockets lying around). We might also get a variety of sprockets and test out how it feels in different configurations.

It sounds like you are not running a reduction between the gearbox and the wheels. I urge you to do this. If you do, you can switch to a single reduction box which will save some weight and efficiency (especially important on a drive like this).

If you really want to save weight, you could integrate your gearbox into the wheel module.

[PAR_WIG1350]

Originally Posted by Jeffy

It sounds like you are not running a reduction between the gearbox and the wheels. I urge you to do this. If you do, you can switch to a single reduction box which will save some weight and efficiency (especially important on a drive like this).

That is one possible improvement, but regardless of whether the reduction occurs inside of or outside of the gearbox, it will still add inefficiency. A double reduction, direct drive gearbox should have similar efficiency and weight as a single reduction gearbox with an additional chain reduction between the gearbox and the wheel.

Direct drive eliminates one axle, 2 sprockets, and one length of chain per module, while adding one drive hub (and possibly an extended output shaft) per module.
Changing to a single reduction and changing the sprocket ratio removes 2 gears, a stub-shaft, and 2 bearings. One sprocket and the gear box housing are also reduced saving additional weight.

If you really want to save weight, you could integrate your gearbox into the wheel module

This is yet another solution with its own pros and cons to consider. While lighter, it could also be more complex and more difficult to actuate due to the additional weight (not an issue with some methods, but if it is retracted with springs, it might not be worth it).

All possible solutions should be evaluated to determine which is best for the team and its goals.

[Madison]

Originally Posted by PAR_WIG1350

This is yet another solution with its own pros and cons to consider. While lighter, it could also be more complex and more difficult to actuate due to the additional weight (not an issue with some methods, but if it is retracted with springs, it might not be worth it).

All possible solutions should be evaluated to determine which is best for the team and its goals.

Imagine moving the pivot outside the two wheels in the module, where 'o' is a pivot, 'X' is a mecanum wheel and 'x' is a traction wheel:

o -- X -- x

This arrangement eliminates the need to lift the modules at all -- either by spring or by other actuation. The weight of the robot itself will cause the module to rotate about the pivot point; you simple need a hard stop somewhere after the traction wheel comes off the floor to stop the module from over-rotating and letting your frame hit the ground.

You can make this sort of thing work by either integrating the gearbox entirely or by continuing to use the pivot point as the link between gearing in the fixed gearbox and gearing to make the wheels spin.

I have a CAD model at home of the module I've been refining. It's not quite done yet, but it is based upon this idea and uses an integrated gearbox. If the above description isn't clear, I'll post a picture when I get home later tonight.