My version of helping hands

September 14, 2012 10:37:06 PM CDT

Stuff you'll need:

1" binder clips:

Binder clips

You can use larger or smaller ones if you want, these happen to work for me.

The bare-metal kind are easiest to solder, but you can use the painted ones if you're willing to scrape the paint off the back and live with the effect soldering heat will have on the paint that remains.

18 gauge wire:

#18 wire

You need to strike a balance between strength and flexibility here. The wire has to be strong enough to hold the work steady, but malleable enough that you can bend it by hand. In my experience, 18 gauge performs well. 16-gauge is stronger but a bit stiff, 20 gauge is easier to bend but floppier.

Stand material:

12-gauge base and stand

I use 12-gauge copper from tag ends of Romex I have floating around, but you can also use coat hanger wire, welding rod, or anything else that strikes your fancy.

The stand above is made from polyacetal (trade name Delrin) that I turned on my lathe. It has a magnet embedded in the bottom, and I use a steel baking sheet as my work table. The magnet holds the base firmly in place, but I can still move things around when I need to. (I'd show you a picture of the whole setup, but A) the sheet doesn't fit in my light box, and B) my soldering bench is a hell of a mess)

For those of you who don't have access to a machine lathe, a block of wood with a hole drilled in it works too.

Construction:

Cut a 3" piece of wire and strip about half an inch of insulation off the end:

Three inches - stripped

Solder it to the back of the binder clip:

Solder the wire to the clip

Then wrap about 1" of the free end around the support wire:

Arm wire wrapped around the 
stand

End of construction.

I don't remember exactly what the box of binder clips cost me (somewhere in the neighborhood of $2.00) so I'll estimate it at about 5 cents per clip. Wire usually ballparks out at about a penny an inch, so a high cost estimate for the clip and arm would be about 10 cents.

Construction goes fast -- you can knock out a dozen of them in fifteen minutes or so -- and it's easy to make a new one on the fly if you need something special in the middle of a project.

You can extend the idea any number of ways.. using alligator clips rather than binder clips at the end of the arms, for instance.

Discussion:

In its simplest form, this is an armature with two degrees of freedom:

  • rotation around the support wire
  • translation up and down the support wire

If you bend the wire in the arm, you get three more degrees of rotational freedom. There are only six possible degrees of freedom though (rotation around X, translation along X, ditto for Y and Z), so some of the rotational freedoms are redundant. That means you can reach some positions in more than one way, which can be handy.

If you make an arm with two coils on it, you can position two support rods relative to each other. That gives you another translational freedom, and even more rotations.

In the long run, there are only two kinds of joints: 'revolute', which give you rotational freedom, and 'prismatic', which give you translational freedom [1]. This technique gives you one of each. If you combine them, what you can build is only limited by your imagination.

[1] - Some of you may be thinking, "so what about a nut on a threaded rod? That translates and rotates!" Answer is, it's a prismatic joint. Yes there's rotation, but the rotation is a function of the translation. If you know the pitch of the thread and the exact distance traveled, you know the exact angle of rotation.

Some shots of the clips in use:

Here's a version where the wire has a 90° bend where it meets the clip:

90 degree arm

The board in question is one of my upcoming SMT tools: a set of six indicator LEDs driven by MOSFETs for high input impedance.

Here are a couple of clips working in tandem:

Arms in tandem

This board is old design based on the hole pattern of a breadboard. I have other designs I like more now, and will get around to posting those eventually.

Random brain cookies:

Genetics explains why you look like your father, and if you don't, why you should.