pic: 816's 2011 Off-Season Teaser

Here’s a little teaser of some parts for our Off-Season Prototype.

First person to guess them both right gets a few EWCPcast Stickers once they’re run. (A week or two from now)

Are they gripper parts? It looks like a pulley with a hex broach and something else with a hex broach

That’s no pulley! (I cannot confirm or deny that I am watching star wars)

I assume I’m ineligible for this…

A little hint to stir the crowd;

It does cool stuff.


Isn’t anything robotics related cool?

A double sprocket before the teeth are hobbed, and the cylinder is likely a wheel hub to be press/cast into a plastic wheel.

No, it is a system for keeping the Fro fluffy.

Dang it.

You’re right, though I hoped that it’d take a little longer to figure out.

The part on the left is a blank for a 22T double sprocket, made from 7075 Aluminum. It’s been broached before the sprocket cutting to make things a little easier for the mill operator.

The part on the right is a ‘plug’ for a 2" wide colson wheel, made from 6061 AL. Preliminary testing shows that the press is good to at least 80 foot-pounds of torque.

(I’ll have to bug you on FB for a shipping address once the stickers are made.)

I’m pretty sure that the smaller item could be part of a cable winch. Could the larger item be an adapter from a hex shaft to a different type of shaft?

EDIT: Dangit, I was both late and wrong.

Oh I see where you’re going with this one Dustin. The topic that we were discussing about makes sense then.

…Or just give them to me for hand delivery dude. We don’t live that far away.

If you guys can wait until Madera I can hand deliver them as long as they go next to the “Powered by…” sticker on your bot :wink:

Drain plug to keep the water out and a small anchor???

I’ve been making a variation of the press-fit Colson hub since 05 using the same principle. If I’m seeing the hub correctly, it looks like its knurled which is something I’ve had great success with as well.

Looking good.


For season I see the resources used to make the double sprockets better used elsewhere, and instead just purchase off the shelf sprockets.

Why do I get the feeling there is going to be a heck of a good time had at Madera?

Hehehehe. I don’t know if you’re fully aware of how ridiculous our current project is.

Brando, Technically the hubs aren’t knurled. The grooving that is visible in the picture was done by running a tool at a relatively high rate across each plug. Technically, it’s not the right way to create a strong press because the cuts are in the same direction as the wheels would see force but I’m very happy with the results so we’ll probably just stick with this method since it’s easy for our Lathe guy to knock out - and it’s pretty easy to replicate in house with minimal skill/effort.

Adam, you’re right on the money with this. I doubt we’ll do a run of double sprockets again unless they’re absolutely needed or it makes sense to do so.

This entire project is heavily influenced by a few factors:

-We wanted to try some new construction methods.
-We wanted to build a lighter more competitive drive than what we used in 2008.
-We wanted to move to an ‘assembly’ style build method.
-The shop foreman at our machine shop told me to design something ‘interesting’ for his guys to make - one thing lead to another and yeah…

Here are some more pictures for those of you that are interested:



I assume your hex broach goes all the way thru the ~2" wide Colson hub. Did you have any issues hex broaching that length? The Dumont literature states the max length of cut is 1-3/8" but that is based on mild steel. I’m curious what it can do in aluminum.

I can tell you from our experience that would likely be a problem and require it to be broached multiple times, or from both sides (with a standard push broach). It’s going to take a LOT of force too, since you have so much tooth engagement.

Where do you guys go for your off the shelf double sprockets?

  • Sunny G.

We just use two single sprockets. Makes all of our drive sprockets the exact same.