Difference between stepper and servo - clarification sought

Hey all,

I'm 90% sure I know the difference, but just wanted to get firm clarification as to when you'd use a stepper over a servo motor.

My understanding:
Stepper is controlled by increments but not absolute positioning. Servo is controlled by position and not so much change

My thoughts on example applications of each:

STEPPER: Altimeter, Clock

SERVO: Airspeed, VSI, Trim Indicator, Authothrottle Control

I would appreciate some clarification on the differences if the above is not true.

Many thanks

Paul

Paul:

You're right on in your applications and range of movements. Other than that, the two have radically different drive signals. For one thing a servo takes +5V and ground (roughly) and a pulse width modulated signal. The stepper needs 4 or more drive supplies to it's internal windings.

I'm guessing by your question and your comments about the two, that you're going to be driving them from a commercially produced driver board, so I won't go into the complete story on the driving signals.

A very good book that you should consider purchasing if you are going to make your own instruments is Building Simulated Aircraft Instrumentation by Mike Powell.
www.mikesflightdeckbooks.com
Mike is very highly regarded in this field.
His book is really full of good ideas and how to avoid the pitfalls.

Mike is also a member of the forum.

Hope that this helps!

Bill.

When we started developping our range of gauges, we already knew that the stepper motor was the best way to drive gauges.
With stepper motors, our gauges could have a depth of approx. 1 inch or 25 mm. This reduces dramatically the depth of your panel and allows for easy access and maintenance. Furthermore it reduces the prices, because there is no housing.
Furthermore, why would you need the torque that is basicly used for wing surfaces on remote controled planes to move a 3 gr needle? And have that needle moved with analogue information?

The use of digitally driven stepper motors allows for a much smoother movements The gauges are moving in exactly the same way as when seen on the panel on screen. In fact, we use the same technology as uses in your car. You would not want the speed gauge to move in a jerly wey.
For traditional gauges (with limited movement) we use stepper motors with an internal stop. This allows for automatic calibration at each mower up.
For gauge that require full rotation, we use stepper motore where the needle position is divided into 1080 steps, resulting in a smooth and precise indication with an extreemly quick response time. The calibartion is done by an electronic sensor that indicates each full rotation.


Take a look at www.flightillusion.com and chack out the movie gallery to see how smooth these gauges move.

What about skips that can happen with stepper motors?