Cody's arm

[Charles King]

You know, I was looking at the 'No.4' pic of your arm and thought, there might be a simple way to upgrade it so it could be spring adjustable. Firstly, what is the length of the spring Cody?  

Author/moderator
Charles King

[Cody Deegan]

The springs I'm using now are 4.5 inches (115 mm).



Spring adjustable?  How exciting!!  That has definitely been an elusive element in my designing.

[Charles King]

I'll do a drawing of it and get back to you. Another question. I have forgotten the weight range of your springs.

Cody, could you send me a close up photo of the arm? Preferably a pic of how the spring is attached to the arm. Then take another one of wide view of arm and the spring. You only have to take one section of the arm.

Author/moderator
Charles King

[Cody Deegan]

These are the specs I got from Century Spring, all in inches:

.75 od

4.5 length inside hooks

11.0 rate

4.0 initial tension

3.5 suggested max def

42.0 suggested max load

.093 wire diameter

music wire material

Two springs a seg.  My sled fully loaded weighs about 21 pounds.

I'll send the pics over.

[Charles King]

Could you put those specs in the metric system - Milimeters. Only if you can.

Author/moderator
Charles King

[Cody Deegan]

19 mm od

114 mm length inside hooks

19.09 kg suggested max load

2.4 mm wire diameter



I assumed the suggested max load was mass, not length, so I converted it to kg.  

[Charles King]

I have not forgotten Cody. Just trying to use paint to make it look nice - but I'm failing at it. So I'm going to try the old fashion way - Drawing by hand 

Author/moderator
Charles King

[Cody Deegan]

No hurry, Charles.  I'm still waiting on bearings for the new arm I'm building.

[Charles King]

Is your new arm going to use the same design or are you changing it altogether? Otherwise I can just scrap this idea I have.

Author/moderator
Charles King

[Cody Deegan]

The bones setup will be the same and the way I attach the springs will be the same.  The only thing I am changing is the vest connector and the elbow joint assembly, so your idea on spring adjusters will still be welcomed - I haven't had any good ideas yet so I was just going to stick to what I know works for me.

[Matic3d]

I've got a copy of the plans (quite nice Cody and well worth the $$.) One idea for adding a tension-adjustment feature without changing hardly anything else is to alter one of the bolts the spring attaches to. What if you had an off-center piece of tubing welded over the bolt that the spring hooks over. Rotate the bolt, and the tubing applies more pull. Tighten it down with a counter-bolt to avoid slippage, or maybe a cotter pin.



Not amazing, but its a very simple approach that gets rid of the need for slides, vise-like contraptions or rack-and-pinion mechanisims, in fact you might be able to add it without hardly having to modify the original design.



The other cheapie idea is to simply buy a miniatrue vise and use it's motion fo pull rather than compress, although you'd have to come up with something clever to lock it down once the tension is adjusted.



 Maybe Cody can come up with an idea, something with set screws and a l-shaped section of metal...  

[Cody Deegan]

I'm glad you liked my plans.  Charles sent me a really good idea for the spring adjusters that would be perfect.  I just haven't had the time yet to actually implement it (thanks again, Charles). It would take a little bit of machining, but I think it is simple enough for a local shop to pull off.

If that doesn't work I'm thinking about developing some adjusters using a motor out of a moped, some telephone cord wire, a knob off my toaster, and a rubber chicken.  I'm sure I can pull it off.

[Phil Kindred]

Hey--that's my idea!!  You're using a rubber chicken--I'm using a real chicken.  I'm glad you missed the the window

shade mechanism.

[Cody Deegan]

I knew it was your idea Phil.  I made sure to erase your copyright symbol before I posted the designs on eBay.  You're lucky I didn't see the window shade mechanism - but that gives me an idea....

[Phil Kindred]

Cody,



My springs arrived today.  They are all your specs except 1 inch longer.  Thanks for the help and hints. Feel free to make the windowshade mechanism your own.