Robotic arm revolute joint design

[murrdpirate0]

I'm trying to make an elbow joint for a robotic arm that is actuated with a stepper motor and two gears. Here's a quick sketch of what I'm trying to do: http://imgur.com/mBlg7

The two bottom plates will be attached to the 'bicep' and the two upper plates will be attached to the 'forearm.' The forearm pivots about the elbow shaft when the stepper motor rotates.

In order to work, the elbow shaft has to be fixed to the upper two plates but free to rotate within the bottom plates. Allowing it to rotate within the bottom plates is easy enough...could probably just provide large enough holes in the plates and let them act as bushings. What I can't figure out is how to fix the shaft to the upper plates. Anyone have any ideas? Or maybe a better way to go about this entirely?

 

[cktoh]

There are different ways of doing this.
1. You can add a collar to the shaft and screw it onto the upper plates.
2. Force fitting of the plates onto the shaft.
3. Add a key to the shaft to help force transmission together with a retaining ring to stop axial movement of plate.
and so on...

I will prefer to use screws..

 

[murrdpirate0]

1. You can add a collar to the shaft and screw it onto the upper plates.

This is exactly what I was thinking, but I can't seem to find any products that do this. Shaft collars are all over the place, but I can't find a shaft collar that can also be screwed onto a plate. Any idea where I can get them?

 

[cktoh]

http://us.misumi-ec.com/us/ItemDetail/10300019270.html

If you design the shaft yourself, you can also incorporate the collar into the shape of shaft.

 

[murrdpirate0]

I had been scouring the internet for at least 4 hours trying to figure this out. Thank you so very much.