PSN-L Message - Subject: Re: Real time traces

= wrote: Hi Meredith, The spring is 17-7 stainless condition C heat treated to condition = CH900. Thickness is 12 mils. The pivots are 2 mil stainless single axis = .. Pivot length is only about 12 mils. They are held tension by the C = spring. A two axis pivot is not necessary. Dave=20

Hi Meredith.

The spring is cut to width on my = personal shear and=20 heat treated in the home oven in the automatic cleaning mode. The = heat=20 treat significantly increases the yield strength. The temperature is = just right=20 as measured with a thermocouple. The width for the instrument pictured = is 16 mm=20 and thickness is 12 mils. (Sorry for the mixed units -- our = European=20 friends will think we can't make up our minds )

I have a large quantity of the = raw material=20 for the springs -- enough for any conceivable quantity of instruments. I = am=20 working on the repeatability in the shearing process. Right now I = can do=20 +- ~.15mm.

As you suggest the period is a = function of=20 the spring length and adjusted at the clamp. It sometimes takes a few = tries but=20 the process is quite easy. The period and rough centering are done = with=20 the center capacitor plate PC board removed to allow for a = motion=20 over large angle for convenience. The final mass centering is done by = adjusting=20 the moveable mass either by eye or using the LED's on the = electronics=20 board with the loop open. The integrator is designed to hold center over = a wide=20 temperature range so reentering is probably not necessary under all but = the most=20 severe climatic temperature changes. We estimate +- 30C but that = is not=20 fully confirmed.

Actuator is homebrew based in a = Neodymium magnet=20 purchased on Ebay. The coil is wound on a modified PAC plumbing = part (1=20 1/4 Schedule 40 plug from Lowes). It takes a few minutes of = lathe=20 work to make it . The coil is 770 turns of # 32 for about 50 = ohms and=20 15 N/A. I fabricate the magnet assembly also but it does take some = minor =20 MIG tack welds. The materials are available from Online = Metals.=20

There is another small mass at he coil = attach point=20 of ~ 10 grams.

The overall size of the basic mechanism = exclusive=20 of the case is 4.5 x 9.5 inches. I have a new (untried) design which = will be 4.5=20 x 5 inches in a somewhat different configuration which may allow = for =20 buoyancy compensation. The new design is also easier to build or = at least=20 that is the goal.

Regards, Dave

----- Original Message -----

From:=20 meredith lamb

To: psn-l@..............

Sent: Sunday, August 16, 2009 = 00:18

Subject: Re: Real time = traces

Hi Dave,

Thanks for the info. Was wondering about the main spring=20 width...its hard to judge from the photo; and where you got such

and the ~ cost? The photo spring looks to be a original = coil strip=20 or a good home shear. I understand (via the web) its

magnetic; but apparently it works fine regardless of the boom end = coil/magnet actuator feedback influence.

Midway atop your vertical mechanism there appears to be a screw=20 adjustable mass balance or centering counterweight.

I presume....that the main spring period is adjusted via the back = clamp=20 alone.

The very small size of the vertical is rather startling = for the=20 ~ giant ~ mechanisms we're used too seeing on PSN.

I can't really tell if their is more added mass to the boom via=20 the photo's besides the ~ frame, coil, capacitance = plate.

What did you use for the coil? Homebrew wound or otherwise = a=20 commerical coil?

What is the magnet, ring ceramic or neodymium?

Take care, Meredith Lamb

On Fri, Aug 14, 2009 at 12:12 PM, Dave Nelson = <davefnelson@.......> wrote:

Hi Meredith,

The spring is 17-7 stainless = condition C=20 heat treated to condition CH900. Thickness is 12 mils. The = pivots are=20 2 mil stainless single axis . Pivot length is only about = 12 mils.=20 They are held tension by the C spring. A two axis pivot = is not=20 necessary.

Dave

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