Monday, December 11, 2006

Back to Valves

My son spent the better part of Sunday machining an adapter to adapt an astroflight brush less motor with 19:1 gearbox to one of the right angle drill mechanics. I tested it this evening and its very disappointing. The sensorless brushless motor does not start well under load. Maston had speed problems with their brushless valve drivers, and I suspect it was because the driver uses back emf to sense the position of the rotor and startup must be slow to get synced up.

I ordered a couple of KZCO valves like the Armadillo team uses and the arrived today. With the top case off of the motor and the cable removed it weighs 1528 grams. With a bit of careful trimming I think I could get it to 1300 grams. My ready to go valve assembly weighs about 1100 grams. My valve is faster, lighter cheaper and and more powerful.

I made a video of the valve operating and just uploaded it to you tube.


Anonymous said...

Looks like you need an encoder on that valve !

These guys make some great and affordable ones:; I haven't ordered any myself before, but I've seen their stuff in many products.

Hopefully you can modulate that well. It almost looks too fast.

Paul Breed said...

Look at the earlier linked valve post. It has an encoder on the valve, its a magnetic non-contact encoder from:

Jon Goff said...

Yeah, you're probably running into similar issues to what we did with the brushless DC drive. Our brush DC systems are much faster, and seem to be working quite well now.


Anonymous said...

Hi, Paul,

Following your progress with interest, and congrats on the "crazy idea that worked" with the PET tank pressure test!" Very fascinating!

A quick question about your valve: in an earlier post, you had noted that a earlier version froze up and burned out the servo when tested at cryogenic temperatures. Was that actually the valve freeezing, or the servo? I was just wondering what differences you expect for this revision. Have you gone with a different valve mechanism, or simply made a higher-power servo?

- Jesse

Paul Breed said...

The earlier valve used a high end RC servo and the servo was just not up to the torque challenge of opening a ball valve at cryogenic temperatures.

I hope to test several different vavle designs this weekend at Ln2 temps.

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