pic: shaft

A 1/8" keyway in an aluminum shaft from our Outback tracks. (Don’t worry, that’s the practice bot from last year.)

I think we’ll attempt to key at 90 degree angles from the old keyway. Maybe. This isn’t my first sour experience with aluminum keyways, unfortunately.

Couple of questions…

  1. What diameter is the shaft?

  2. Why aren’t you using steel?

This year we are trying live aluminum axles for the first time. We chose 1/2" hex, hopefully they hold up.

Steel is real man…

Unless you are completely strapped for weight, drivetrain shafts should be robust enough to get through a competition maitnenence free (just opinion here).

Without a working drivetrain you may as well just put a battery with a team number and a flag holder on the field!


Looks like a nice shaft…from the left of the damage. Is that 6061, 7075, or 7068?

Do the Outbacks come with that Aluminum shaft or did you just make it yourself? If they came with, then they seem to be the Banebots of last year.:ahh:

The shaft came from the Outbacks we bought last year and are using as a practice bot, didn’t know they were aluminum until a few days ago. I would never use aluminum axles :stuck_out_tongue:

There’s no way those are 7075 or 7068, or anything stronger than 6061. We’ve been using 7075 for years, and we’ve used and abused all our robots. We’ve never even seen serious wear to a keyway in 7075, letalone something as mangled as this.

I wouldn’t look at this as a testament to why steel is better. I’d look at it as a prime example of what happens when you choose the wrong alloy material for a high stress application. Many teams have been using aluminum shafts with great success. There really is no reason to use steel, if you have the proper machining resources to make your own shafts out of Al.

6061 isn’t a great alloy for transmitting torque through keyways or such things with high stress concentration factors. 696 used 1/2" axles with 1/8" keyways out of 2024 Aluminum (McMaster pre-keyed stock) last year with 5" wheels geared for 9fps with two CIMs on each side and never had a problem with them over two regionals and championship. But 6061, I doubt it would have survived.

Another important thing is to make sure your key fits tightly with no backlash.

Looks like the key was shorter than the keyway, which would halve the load the keywayt would be able to withstand. Was that the case?:slight_smile: :slight_smile: