securing leads and components on rotating machinery

[Tmoose]

Is there a good reference containing guidelines for securing wiring and components on rotating machinery.
We make an 1800 rpm device with a lot of boards, leads, connectors, capacitors, etc. We've spotted some problems by watching the device at speed with a strobe light, but I'm hoping there is a MIL spec or something that spells out some good rules of thumb and examples.

Thanks,

Dan Timberlake

 

[VEBill]

Yikes... Assuming the math is correct, 1800 RPM with a radius of <FOR EXAMPLE> 27.6 cm results in centrifugal forces (or more precisely, 'centripetal acceleration') of 1,000 G. If the radius is greater, so is the G-force in proportion; and less is less.

Just one of many on-line RPM-G calculators:

http://www.eppendorfna.com/support/online-calculator.asp

G-force goes up as the square of the RPM and in proportion to radius.

High hundreds, or a thousand, G is a lot. Rim speed for the example is about 187 kmh or 116 mph.

Suggestion: If you haven't already, install an unbreakable plastic shield before someone loses an eye. Especially if various components and hardware are flying out at random intervals. Red tag the power switch if you haven't conducted a safety study.

If this RPM is an operational requirement for the system, then it should have been identified as a significant issue at the outset. Similar to, "Oh by the way, the entire Command and Control System needs to fit through a 4-inch inside diameter pipe..." ;-)

Epoxy potting is probably going to be required all over the place. Then you'll have to rebalance. Structural analysis of the major components: PCBs and everything.

Standby in case anyone has actual hands-on experiance at these levels and better hints.

Yikes.

 

[Tmoose]

About 16 inch max diameter on this particular item.

We are designing and making it, and the electronics group comes up with their own specs and is mighty "independent".

 

[ScottyUK]

We have a small electronic unit mounted on a turbo-alternator shaft of similar - slightly larger - dimensions rotating at 3000rpm. The housing is machined aluminium and the electronics is potted in epoxy resin. We experience a lot of problems which we attribute to factors such as bond wire failure within semiconductors and deformation of capacitor electrodes leading to cap failure. Eectrolytics are a waste of time for this application - we have enough trouble with polypropylene film types.

It is a tough environment - we see casualties quite frequently, and it seems to be inherent in the application. Any chance you could get the assembly closer to the shaft centreline? That would be the best way of reducing the forces on the components.

Perhaps the military avionics guys might have some more ideas?


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I don't suffer from insanity. I enjoy it...

 

[VEBill]

Avionics for manned aircraft only sees perhaps 10G. 30G is a common requirement for crash safety, but it simply needs to stay attached to the rack (need not function afterward). Missiles can see much more, but not a thousand. Shells obviously have HUGE peak loads.

 

[IRstuff]

The only other military application that comes close is anything that's MIL-S-901D shock qualified (the infamous hammer or barge test). In case you're unfamiliar with the barge test, the unit is mounted on a barge in a pond and depth charges are set off in the water. Pretty spectacular, all in all. The ones that have to operate afterwards survive several hundred g's

High speed watercraft experience up to about 100 g's but extremely short durations. Nonetheless, the most frequently broken item in our system was a load bearing.

TTFN

 

[VEBill]

Shock loads can be absorbed with shock mounts (as found underneath Naval systems). Constant Hi-G loads require a different approach.