Spring Tension Adjustment

[Brett A. Noe]

Hey Cody,



I spoke to Charles on the phone yesterday. During our discussion, he mentioned the idea/design for a spring adjustment method for your stabilizer plan.



I thought I'd give you a holler and see if this is something you're comfortable sending me or posting. I'd be willing to be a guinea pig to test it.



Send a message to my account if you'd rather continue this privately.



Brett

[Cody Deegan]

Charles had the idea of machining a plug with threads that matched the inner coils of the spring.  In the center of the plug would be a tapped hole to accept a bolt.  This plug (or bushing) could be screwed into the end of the spring.  You'd have to remove the looped end of the spring first.  

Put a hole in an angle bracket large enough to accept the new bolt and then attach the angle bracket to the front end of the lower bones.  



The only reason I never included this idea in the plans was because I was trying to stay with the theme of no machining.  I had already been experimenting with the angle bracket, but was unable to find a suitable piece to attach to the spring.  

[cosmin rotaru]

That's the plug I've used in my arm. I was afraid it won't work (the spring would slip or something) but it worked great! And I only had two coils of the spring on that plug!  

Cosmin Rotaru

[Cody Deegan]

That's good to know.



By the way, what are you working on now, Cosmin?  Have you started building another rig yet?

[Brett A. Noe]

How about something like this?



This is using an eye bolt instead of a bolt and machined plug. You could also use another nut on the other side of the L bracket to lock it in position. I thought of this or a small turnbuckle like those below.



The turnbuckle could have one eye around the bolt shown in the existing plans.

Just a couple of ideas. I personally like the eye bolt/L bracket combo myself. I think I'm gonna try that when I build my rig.

Brett

[Cody Deegan]

The eye bolt won't work.  I already tried it a long time ago.  The problem is this: say you want to add some tension to that spring so you start tightening the nut.  By doing so, the threaded end of the eye bolt begins to protrude very far out in front of the arm segment.  Now this isn't a very big deal for the front segment, but it is for the back segment.  Your elbow joint will undoubtedly hit the bolts on both sides and freedom of motion will be restricted.  It just won't work.



The turnbuckle is a better idea, but turnbuckles are so long.  Your spring would end up being maybe two inches in length at the most.  I don't foresee that working very well.

[Charles King]

The turnbuckle is a better idea, but turnbuckles are so long. Your spring would end up being maybe two inches in length at the most. I don't foresee that working very well.

A suggestion, perhaps?

  Depending on the length of the turn buckle and how much space is require.Why not just cut the turnbuckle to fit the length of the space needed, with a metal cutter?

Like I said, it depends how much space is available between the spring and bracket for the nut and, how much thread is left in order to get some tensioning. Either way you will end up shortening the length of the spring any way. It might just be a little of the spring in order to get the space needed.

Charles King          

[cosmin rotaru]

"By the way, what are you working on now, Cosmin? Have you started building another rig yet?"



I'm still at designing. Is not like I've been doing A LOT of designing. Is just that "the job gets in the way.." like you said it in another topic...



I talked with a machinist last weekend: he has CNC's and all, it seems. He thinks he's up to the task!  So this weekend I hope I'll meet him again and challenge him with the GIMBAL! If he can do that, he can do it all!  

Cosmin Rotaru

[andreas kielb]

I used turnbuckles for the tension adjustment and I'm very happy with them. It is also a very simple solution to get the ball rolling 

It is true that you need quite short springs but that doesn't mean that they are weak - it is more like the opposite (.. they are little beasts  ). If you wonder what springs I use I bought them here (types T32470 and T32680) : http://www.febrotec.com/produkte/zugfedern_a/Zug_a16.htm (...the list is a good survey as well).

cheers,

Andreas

[Brett A. Noe]

Here's another idea...



This would replace the plug with a wing nut. Seems like it would work. At least theoretically ;D

Any comments?

Brett

[cosmin rotaru]

A reason for the plug you're trying to avoid, is to get rid of the loop at the end of the spring. It is known to be the weekest part of the spring. (I broke on of those loops and then I decided to pay someone to make me the plugs!)

Cosmin Rotaru

[francoinmontreal]

I just saw the discussion going on about tension adjusters and thought I'd give you my 2 cents. What if you used a system like the one sugjested in the drawing (with the eye-bolt...), and to make sure that the srping didn't twist under the torque of turning the screw on the eye bolt, you had a flat machined along the lenght of the eye bolt, with a matching hole where it connects to the arm? Some bushings have this flat in them already. If you could find a bushing like this, all you would have to do is press-fit it into a hole in the aluminum, and voila. A twist-less tensionning system! Since these bushings have a flat on the inside, the outside is round and so no special kind of tool is needed to make the receiving hole for it. Anyways just an idea.



Franco  

[Brett A. Noe]

I'm just trying to avoid the plug for the reason Cody mentioned above, The plug requires machining, the other methods do not.



In any case, I think I might try the turnbuckles. It's only going to cost about $3 to try them, and requires no mods to the existing design. (With the exception of a few springs.)



Brett

[brucefin]

Since I'm about to embark upon my arm-building adventure this issue has been gnawing on me.

How much play are we really looking at here? I'm assuming that I will use the spring combinations Cody so assiduously tested and mapped out for us in his plans when any gross weight changes are involved (i.e., swapping my GL1 for my XL1). Spring tension adjustment should really be just for fine tuning. Metaphorically slap me upside the head on this if I've got it wrong.

If such is the case, how much adjustment is needed? Are we talking 1 inch, 3 inches? I ask because if it's small enough I think I can get away with using an eye nut instead of an eye bolt. The problem is you can only adjust it by the distance inside of the eye.

What say ye, oh learned ones?

Bruce

[Cody Deegan]

Me personally, I'd want to have a couple inches of adjustment.  That is a good question though.  How much adjustment do others have on their rigs?