pic: Concept Octocanem Drive



My first impression is that there may not be enough stiffness to the module bending/twisting… Is that .25" thick plate with .25" wide ‘struts’? It’s good to see all the standoffs, but I’m concerned they’re also too thin and that the plates won’t have enough stiffness to avoid bending between/around the standoffs anyway. Perhaps go up a little wider on the struts? A gearbox might be fine like that, but in a spur gearbox there are essentially no loads trying to bend the plates of the gearbox… this is not the same loading case.

Which wheel is the pivot? How are you going to drive the first wheel? How are you going to drive the second wheel from the first (looks like there may not be a clear path for a chain/belt currently)?

It looks like those are 6" wheels… are you sure you don’t want to use 4" and smaller wheels? It’ll make your module way smaller, lighter, shorter (less of a moment arm for the side-loads of the articulating wheel), and means you need less of a gear reduction before the module to get a given speed.

My first impression was “Why are there rollers missing?”

More seriously, can you (Garrett) explain why certain design decisions were made with this concept?
Why is the metal so thin? Why use 6" wheels? Why not use two different diameter wheels to perhaps achieve some sort of speed difference between the two modes? What is the intended use for this module?

I know it’s titled “concept”, but these are all questions that need answering, as without answering them quantitatively, you’re not really engineering, just doodling cool stuff in CAD (and if thats what you want to do, by all means do it). If this is a serious consideration for future use you have to understand the design decisions you make.

Perhaps that’s the experimental aspect of it- maybe the 2/3 mecanum wheel allows for improved traction. Or something. :stuck_out_tongue:

Either way, good start! Like Kevin said, try making the traction wheel smaller, as it will allow you to use a 1-speed gearbox to get 2 speeds.

To answer the most pressing question, the mecanum has missing parts because… they were accidentally deleted from the model in my library. :o

Now about the design, I originally based this module off a picture of 1540’s drivetrain from this past season.
They had quite a bit of lightening done on the module and originally I thought their strut thickness was .25", but looking at it again, it appears closer to .5".
I was figuring that the struts were on the thin side.

My reasoning for the wheel sizes was that A: my team owns 6" mecanums from this past season.
And B: I wanted to keep the connection point for the piston as close to the traction wheel axle as possible without needing a longer piston or having a larger radius of rotation for the traction wheel.
However in doing so, I overlooked the fact that the mecanum and the traction wheel need to be at very different speeds :o
So the next iteration should have a smaller traction wheel.

Yes, there is enough room to run the belt past the stand-offs. The belt is c-c and a tight fit. So there shouldn’t be much drooping in the belt.
There is a decent amount of clearance around the 24 tooth pulley.

The actual gearbox system will be very similar to this set-up.

I’ll post the next version after the weekend when I have some time to work on it.

Thanks for the feedback everyone!