Cantilevered Wheel Shaft Strength

Our team is strongly considering going for a west coast style drive where the wheel shafts are cantilevered, but we’re a little worried about strength, and how to make it stronger and we were wondering if any teams could speak to the strength(or weakness) of a system like this.

We are still deciding on if we will be using dead/live axles. I am leaning towards dead axle because I feel that placing a thick block of aluminum inside of some box tubing and putting a 1/2" aluminum shaft (maybe steel?) shaft will be stronger than supporting the shaft with bearings.

So my question is- Are cantilevered wheel shafts really strong enough?

We use a west coast setup with the 1/2inch aluminum hex shafts from vexpro. our robot twice fell 4 feet off the tower last year onto the wheels. the wheel shafts were fine.

I cannot speak from personal experience but I can tell you that teams (254 and 118 come to mind) have been running cantilevered shafts for years with great success. I would look at their past robots, the VEXPro VersaChassis and some of the chassis offered by 221 Robotic Systems for reference - plus I know there are a number of people on this forum who can give you a little more detail.

We have used direct drive two or three times, in each case with a live shaft off an AM Toughbox tranny. We have had no problems with the drive.

I know a few bots with cantilevered 1/2" aluminum tube axles. Yeah, they are.

The team to ask is 254. They’ve done this since 2004, and have won around 20 regionals with this setup. I can’t speak for them, but I’m pretty sure that if strength was an issue, they wouldn’t use a drive that is too weak for 10 consecutive years.

What I would be interested in knowing is how often these teams change out their wheel shafts or tread.

Vaguely they are strong enough. We use 1/2 inch bolts for dead axles on either end and a hex 1/2 inch steel shaft for the center. If you want, I already have a CAD model (Inventor) of our WCD drivetrain that I can send you to give you a starting place.

Keep the length of the cantilever as short as possible. Avoid notches, holes, diameter changes, or other stress concentrations in the cantilevered portion of the shaft. .5" round or hex steel (4140) is pretty darn safe. If you’re going to use aluminum you should do some math (Google for cantilevered beam equations and allowable stresses for your shaft material). Hint: has some nice 7075-T6 .5" hex shaft stock available.

Tread: a lot. Wheel shafts: Never.