Alternative to Air Core Movement

[smendlik]

So I read through Mike Powell's books and really want to make some gauges. One thing though, I really don't want to wind the core for air core movements so I began wondering if a servo or stepper motor could be used in place of the air core? If so, what would it take to make that happen?

[Mike.Powell]

The guys over at Viperpits.org have been successful purchasing air core movements from Simco http://www.simcoltd.com/specialty-oem/micro-air-core/ I think they just had to meet the minimum order quantity.

If you don't need full 360 degree motion you might look at the Switec geared stepping motor meter movement. http://www.switec.ch/products/switec/switec.html There are a couple of vendors on Ebay selling these movements as replacements for automotive gauges.

[smendlik]

Thanks Mike, I'll check into those links as soon as I get a chance. Stepper motors will do full 360's, right? So, if no other option presented itself steppers could be used in place of air core movements?

[Mike.Powell]

Stepping motors can be used to make gauges. They aren't drop-in replacements for air-core movements as they require different drive waveforms. A 400 step per rev motor makes a nice basis for a gauge. It's powerful enough to move heavy mechanisms like those in an artificial horizon, and has small enough step size for smooth movement without gearing. These motors pop up on surplus electronics sites every so often. Unfortunately, right now I'm only aware of sources for new motors. (for example the Jameco Electronics #1581231 at $19.95) You can certainly build a guage using smaller, less expensive stepping motors having large step sizes if you gear down the movement.

The Switec geared stepping motor meter movements used in automotive instrument panels typically have a built in stop. This is used to reset the gauge position on power up. It might be possible to open the motor and remove the stop.

Don't dismiss making air-core movements. A year or so ago I revisited the DIY air-core design. Cylindrical neodymium magnets and sewing needles come together to make great rotors. Winding is still the least enjoyable part, but a simple jig can make winding them tolerable. There are some pictures on my site here: http://www.mikesflightdeck.com/diy_aircore_instruments.htm. The newer material is at the bottom of the page.

[smendlik]

Mike - Thank you again for your detailed and extensive reply.