OT: RC Analog Servo?

(alt.stuff trimmed because GigaNews doesn't seem to like me posting there)

Possibly nowhere. The 270 degree rotation is a barrier, as is the 5/8" height. Finding a servo that's less than 5/8" thick across the direction of the output shaft is easy, but finding one that's less than 5/8" high is well nigh impossible.

Also, they almost universally rotate 90 degrees when given pulses of the standard 1ms to 2ms width. Some will gracefully go up to 180 degrees, but the feedback is almost universally with a pot that almost universally has a dead spot around the extremes that's close to 90 degrees wide, and they usually have mechanical stops that limit travel.

You'll probably get there from here a lot quicker if you can figure out a way to use a 90-degree rotation device to get what you need at your end- effector; if you can't do that then you may need to whomp something up yourself.

To find lots of regular RC servos, look in any old hobby shop. Robotics suppliers have them, too, and are probably more likely to have something like what you need.

Servos usually have the shaft coming out of the short edge. You can get continuously rotating servos, but they generally don't have encoders.

One good place to poke around is servocity.com--they have e.g. the Hitec HS-785HB that goes 3.5 turns.

All I need to do is move a pointer. I may just roll my own two-coil indicator ala Stewart-Warner... I did a Stewart-Warner indicator driver chip design BC (before CAD ;-)

Power is no object, AC power available. ...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

How about a small stepper motor? I don't think there are any RC servos that thin (5/8 inch).

Adafruit do these guage servos used for car instrumentation. 9mm thick and

Not pure analog but I have used them successfully.

Andy

form factor.

You can get small stepping motors that are designed for the task of operating a pointer as well as the air core movements that you are talking about.

They're automotive so not so easy to source in small quantities, but there are cloned ones to replace GM parts (presumably because they fail so very much).

Do you know of a source of the air core movements?

Back when I was designing alternator regulators (at Motorola SPD) we had a huge test stand running maybe 50 alternators at a time... the GM alternators failed at almost precisely 50K miles, just out of warranty... bearing failure. I always marveled at their ability to do such precise engineering >:-} ...Jim Thompson

Aha! Good link. Thanks! ...Jim Thompson

This guy will sell you single stepper motors for GM crap speedometers. I had mine rebuilt and the price was not too awful. From memory, I think they are about 1/2 inch thick. He is also very helpful should you want to rebuild it yourself.

regards

Find an aftermarket speedometer that runs off of pulses from the tranny pick off, and generate the pulse train any way that works. A tachometer would probably work, too. It'll be a simple frequency to pointer position conversion, with no pulses being 0.

Just be sure to get one that lets you disassemble it if you want to replace the scale.

Search for micro RC servo like these:

MMMmm...not exactly a servo,but has complete 360 degree capability and built-in "encoding"; only problem may me the thickness. What am i talking about? The selsyn synchro servos. See: