South Pole Diaries 1997/98

   

   


Friday 21st November 1997 - Going backwards

From John Storey.......

Since we're clearly getting on top of things in the AASTO, we decided to start the day by hoisting the Australian flag high above the green and gold structure. And very splendid it looks, too.

Today should have been a good day in which we finished assembling the stepper motors on the NISM and MISM, boxed them up, and spent the afternoon doing rallycross in the Sprite. Alas, it was not to be.

Things started badly when we fired up the NISM one more time to set the stepper motor rates. There was a fizzing sound and smoke started rising from the power supply card. We switched off in a hurry and pulled the card out, but none of the components I touched was hot (that's the problem with surface-mount chips - no thermal mass!) Nothing for it but to plug it in again and watch carefully. Sure enough, little red sparks and wisps of smoke, not from the main board (built by our normally excellent electronics workshop), but from the exquisitely made Maxim card. The board was still working just fine, and it turned out once again to be a surface track of black crud. I scraped it of with a scalpel, and it's good as new. (Ev Pascal, professional electronics engineer, says it sounds like scraping toast when we're fixing our boards. It seems he hasn't struck anything like this previously in his career.)

MORAL: make sure all the boards have all the grunge cleaned off them.

We took the moral to heart and carefully cleaned the connector that couples the stepper motor drive signal to the MISM (all of the mil-spec coating came off in the process, leaving bare aluminium). All we did was dunk it in water, then rinse thoroughly in a trichlor/isopropyl alcohol mixture out of a spray can.

Then we plugged it all together and... horrors! The clockwise limit switch ceased functioning. With the stepper motor developing more torque than a D9 and heading relentlessly for the limit, we quickly pulled the plug. (Andre: the Fluke takes up your offer of 10:1 on a non-catastrophic stall, and wants to take odds on Ant rolling the Sprite.)

To cut a long story short, it turned out that the plug was still wet and this was shorting out the limit switch.

MORAL: After you've washed things, dry them.

It would be handy if the software command "rotstat" told you what the limit switch readings were, to aid diagnosis.

Clearly we need to think carefully about how to clean up the electronics boards (and connectors) before we can turn our backs on this thing.

The good news is that the stepper motors really do have huge amounts of torque, even at the 114mA "normal power" of the old motors.

At the CARA meeting on Wednesday I asked again for a fire extinguisher. The reponse was that this did not seem to be a very urgent request, and when did we think we'd really need it by? I suggested that we'd like it just before the fire started, please. This scored us a laugh, but no fire extinguisher. Yesterday we tried a different tactic: we *didn't* ask for a fire extinguisher. This morning there were *two*, sitting either side of the AASTO entrance door.

We now have in our possession "AASTO #1", the first JAZ disk of housekeeping data. Does anyone in Sydney think they know how to read it?

Nothing really funny happened today. I washed my clothes, had a shower (this is a major event at the Pole), and read my "newt" email. Ev Paschal fixed the noise problems in the DCU by putting little capacitors and ferrite beads here and there, and never once made a sound like scraping toast. The AGO service crew arrived, looked around and said "Oh boy", and will come back tomorrow and try to fix the TEG. Ant and I will work somewhere else, as we alreay know the TEG is full of rockwool - one of the worst substances in the known universe after brown slime.

Tonight the crane is coming to lift GRIM off SPIREX. This marks the beginning of the Abu project - something that should have happened three weeks ago. Al Fowler and Nigel Sharpe arrive tomorrow.

The "super" hasn't made its "mating wasps" rebooting noise since we replaced the GoodWill supply with the Lambda.

The wind has dropped to below 10 knots, so we hope to get on with the other tasks like pulling the AFOS down in the next day or two (thereby avoiding the rockwool).

John

 

 

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