Where to get gauge needles?

[Mike.Powell]

Here's a nice little stepping motor I haven't seen used much by DIY instrument builders. It incorporates reduction gearing so you get relatively smooth movement from a very simple motor. It has an internal stop so you can't use this model in applications like compasses that require unrestricted rotation, but it does do away with the need for a shaft position sensor. To initialize the shaft position you simply step counterclockwise long enough to be sure the motor is against the stop.

These units are used in automotive gauges. I bought a couple through Ebay as replacement parts. Cheap$!


If you plan on using RC servos, you might not be aware of Servo City, a supplier of all sorts of useful servo-related items. In particular they sell gears that fit the end of RC servo output splines. http://www.servocity.com/html/gears___sprockets.html

If you're looking for information on how to build instruments, there are a few pages on my site that overview the topic.

http://www.mikesflightdeck.com/DIY_s...nstruments.htm
http://www.mikesflightdeck.com/DIY_s...nstruments.htm
http://www.mikesflightdeck.com/diy_a...nstruments.htm

[cscotthendry]

does the PM20S have enough resolution with only 20 steps? do you use additional gearing? I was under the impression I would need 1.8deg stepper motors.
I'm trying to build the flaps gauge and a wet compass
Thanks!

Yes, the PM20S is pretty low res, but you can overcome this by a)Half stepping (See Mike's book about that) and b)Single reduction or compound gearing (Again, see the altimeter project in Mike's book, or my altimeter)

Servos are good where the gauge doesn't have to go full circle. They can be made to go full circle by removing the internal stop, but then you're back to needing a home position sensor of some kind and no better off than using steppers. I prefer to use steppers where possible as the signals that drive them don't require as much critical timing code to run them as do servos. However, if you're using a ready-made solution such as an open-cockpits, phidgets, or similar driver board, then you don't have to worry about it.

For your compass, I'd use a stepper. For the flaps gauge, I'd use a servo or those steppers that Mike posted pics of.

Mike: Do you have a source for those steppers that can supply them on demand?

[Mike.Powell]

Mike: Do you have a source for those steppers that can supply them on demand?

There are at least two vendors on Ebay supplying those stepping motor movements: "digital_dash_solutions" and "mandigital". See Ebay items 220495246141 and 230409622645 for examples. I can't remember who I bought from, but these vendors appear representative.

[cscotthendry]

There are at least two vendors on Ebay supplying those stepping motor movements: "digital_dash_solutions" and "mandigital". See Ebay items 220495246141 and 230409622645 for examples. I can't remember who I bought from, but these vendors appear representative.

Those look pretty neat. I have a few questions that the eBay sellers don't mention:

What diameter is the output shaft?
How far does the output shaft turn end to end?
How many steps does it take end to end?
Are they unipolar or bipolar?
Are they 12V or 5V?

Thanks

[Mike.Powell]

Here's a link to the manufacturer's product information page. You can download a spec sheet from it. http://www.switec.ch/products/switec/switec.html

[cscotthendry]

Thanks. It's a Swatch!