Friday, May 17, 2013

Spider Project Part 3

Okay after a slight break from working on this project to attend to other things I've finally gotten back to it.

I realized that I had a design flaw in the cam mechanism that had to be remedied or this thing would never work like I wanted it to.

The Problem

The cams where wiping down the follower arms which was causing some of them to get stuck.
They also were getting caught on the edge of the caps I was using as followers.
This was causing it to take too much effort to turn the crank and was causing a very uneven motion.

The Solution

I put 90 degree angles on the ends of the follower arms.
This did two things: 1. Kept the cams from contacting the arms and 2. got rid of the lip that the cams
were getting stuck on.

See How Nice It Works
video
It is also much easier to turn the cam by hand now.

The Whole Enchilada
video
In this video, the back end (ahem) of the spider is facing the camera.
The movement is a bit squirrelly with the drill but looks better when done by hand.
If you really want to track the legs movement play the video on slow.
I'm personally leaning towards the idea that the jointed-muscled legs are more trouble than they are worth.
I do like the motion, how the legs reach out as they come down.

Another thing that I realize is that the 'return springs' are not optional. Even with this newer more efficient drive train I feel it still takes too much muscle to turn the crank without them and they keep the followers from falling off the cam.

The Plan
Start converting this prototype into a 'real mechanism'.
I will replace the wood structure with a light weight minimalist metal frame.
I'm going to have to farm out the fabrication of the cams. I think that using UHMW plastic for them is a great idea. I need them to be perfect and a CNC mill can whip them out in like 5 sec.
I haven't decided if I can just use the followers as is or if I need to redo them also.
It seems like the PVC wiping on UHMW plastic should last forever.
The grey PVC pre-bends riding on a threaded rod I'm not so sure about.
Using the 1/2" PVC for the legs doesn't seem like a problem for me.

Okay, anybody have any ideas?

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