Octagonal WCD

[Ty Tremblay]

Originally Posted by craigboez

Care to share your calculations? And how do you determine the magnitude of the load you'll expect to see at a corner wheel?

It was quick and dirty, but here's what I did:

A worst case scenario of running into a robot at full speed with a high COG could lift the back 4 wheels off the ground. I chose this as starting point. Assuming a full weight robot with bumpers and a battery (~150lbs), that means we've got about 75lbs on each of the two wheels still contacting the ground.

I happen to be designing a very similar drivetrain, so I took my most cantilevered wheel and did my analysis on that. My colsons are cantilevered such that there's a 1 inch gap. I then threw all of this into SolidWorks SimulationExpress and came up with a minimum factor of safety of 3.074 right next to the bearing where you'd expect them the shaft to shear.

The above was done with 7075-T6 Aluminum. If a FoS of 3 still leaves you uncomfortable, you could easily go with steel shafts and never have to worry about them breaking.

Originally Posted by craigboez

Another aspect of this design that is still TBD is the way the bumpers integrate. I'd like to incorporate a latch like 971 and 254 and Spectrum have shown. The Skunks posted another variation of this a few days ago using a different type of latch. Making a solid connection on the "wing" area is my biggest concern. Any good ideas on this?

I followed the 971 method of bumper attachment, though it's not 100% fleshed out yet. The important part is to have a well constructed, single piece bumper. Here's what I have so far.