Servo's or Stepper motors?

Projects General Guidance
1

I want to create a little project using an uno, into a car dashboard, I would like to have two analogue style gauges for speed and RPM, and an LCD display for temperature, and other information.

First question really is what would you advice I use for the analogue gauges, stepper motors or servo's? I do want to try and keep this project cheap, but if one is better than the other then I am all ears.

Thanks
Jim

2

Servos will be much easier to implement than stepper motors and probably much cheaper. You can buy small servos for under £3. Moving an analog needle won't require any significant torque.

I suggest you buy a small servo and experiment with it to see if you can get it to behave as you wish. It should be possible with careful programming (nothing complex) to make it move either smoothly like a modern instrument or in a wobbly way like an older instrument.

I can't think of any way in which a stepper would be superior. You should be aware that the usual range of servos can only move through about 180 degrees. If this is not enough you can buy servos with greater movement (e.g. a sail winch servo) which might still work out simpler and cheaper than a stepper.

...R

3

Thanks for the info Robin, I guess 180 deg would be enough for me, so I'll have a look for some cheap servo's and have a play

4

if I used something like this:
http://www.ebay.co.uk/itm/Feetech-360-Degree-Continuous-Rotation-Servo-3kgcm-FS5103R-Arduino-Raspberry-Pi-/321280971134?pt=UK_Computing_Other_Computing_Networking&hash=item4acdd6917e

would it be easy to "zero" to find a start position?

5

There isn't any "zero" position for a continuous rotation servo. You would need extra components to detect where the servo arm is pointing. That will require a lot of extra construction and extra programming.

If you need more than 180 degrees a sail-winch servo (which moves through about 900 degrees) should only cost about £10. They do allow position control and the extra cost would be quickly offset by the ease of use compared to a continuous rotation servo.

Obviously the cheapest option is to stay within the 180 degrees of the normal servos. Or maybe you could use a 2:1 gear system to give 360 degrees - probably simpler than putting sensors on a continuous rotation servo. A lever system should enable the 180 deg to be increased to (say) 270 deg or maybe more.

If you do need a continuous rotation servo it is easy to convert a normal servo. Google will find several instruction websites.

...R

6

You don't want a 'continuous rotation' servo. These are ordinary servos which have been hacked about to break the position feedback mechanism so that they just act like variable speed motors. This is completely unsuitable for this project, what you want is an ordinary simple cheap servo. They're available with a variety of ranges of motion and I suggest you just need to balance the cost versus functionality and pick the type that suits you best. If you can put up with about 180 degrees of travel, you would only need to spend a couple of quid per servo.

7

thanks for the info guys. I've ordered some 180deg servo's to have a play with. I'll go and have a search now for servo control.

8

if you have an old scanner or printer or floppy drive, you might be able to find a stepper.
very easy to control the small ones. 4 pins are needed and 4 transistors.

some are 200 steps per rotation, on a scanner it might have a second gear attached that would increase that to 5:1 or 6:1

you might have fun learning about steppers.