arm keeps hitting itself

[caine chow]

Hi,

I just completed the rig, thanks for everyone who helped me answer my questions on this site.

I went to test it for the first time, when I started walking, the first arm keeps hitting itself, and touching my body. Is this normal during operations?

thanks,
caine

[Michael W. Niece]

It's been my experience, having built Cody's rig as well, that the arm's vest-attaching part isn't perpendicular to the ground ... it's not level.  When the weight was applied to my vest, it pivoted at my shoulders slightly and moved the connecting plate outward (mine was back-mounted, so a front-mounted vest would lean into a person's gut).  When that happened, the arm had a tendency to swing away from me because gravity pulled it outward (the arm was, after all, pointing down at about 2 degress).  From the looks of your photo yours isn't level, either.  Of course, it may be the way you're standing or maybe the camera angle misleads the perspective view.

To fix it, I first made sure the vest was completely snug, front, back and shoulders.  Then, I modified my vest attachment piece so it could be "rolled" to correct a non-horizontal level.  So basically, it's most likely that your arm and notably its joints are not level.  Use a bubble level on the elbow joint while you're wearing it to find out.  Keep in mind, too, that the arm might also be leaning into or away from your sides.  So be sure to check both the roll axis and the tilt axis.

It should be said that my solution fixed my rig after I troubleshooted (?) my symptoms, which happened to be the same as your symptoms.  Other people might have better answers.  Good luck!

-Michael

[Charles King]

On another note Caine, it seems the springs in the arm closer to the vest has a snag in it. In other words its not straight or perpendicular to one another.

[Michael W. Niece]

Charles, I didn't even notice that!  Of course, it looks as though the spring is "shortened" by running an eye-bolt or something like that through it.  It looks like the spring is supposed to do that, in a sense, because of how the bolt comes through it from the bent end.  Of course, having uneven tension won't help matters!

-Michael

[caine chow]

still haven't got a chance to fully test it, but seems to work better now, thanks

[Burt Johnson]

Hi Caine,

Nice looking arm...But I don't think your springs are the exact ones called for in the Cody plans and it should not be buckling (lower left hand corner of your pic) like it is. It should be straight and taught in any position. Also the pivot points on your elbow look like there is too much slop (the holes in your steel channel stock are larger than the bolts that are going through them) which allows too much unwanted motion when it bends like a hinge. Which makes the elbow too loose and would be the reason for it hitting like you describe in your post. I could be wrong about this, however a good test is to take your arm in your two hands and grab each end of it. You should not be able to twist the two ends of the arm out being parallel to each other. If you can twist the arm in this way I would check out every pivot point on the arm and do what you have to do to eliminate any of the loose joints.

Burt

[Burt Johnson]

Caine,

One more thing I would suggest that you cut off and deburr any bolts that are longer than the nuts.
You could get a nasty cut on your arms if you don't. Ouch!

Burt

[Ceran Thomas]

Caine,

One more thing I would suggest that you cut off and deburr any bolts that are longer than the nuts.
You could get a nasty cut on your arms if you don't. Ouch!

Burt

I have some parts thet need finer polishing of sharp ends.  What would recommend best method be?

[Burt Johnson]

Ceran,

check out the 3M Scotch-Brite wheel here:

http://www.levineautoparts.com/3mscbemowh.html

It is the defacto standard in the deburring and polishing of any type of metal used by professionals.

Burt