suggestion for motor selection(stepper or DCMotor)

[fever]

hello all,
My project involves moving a plate mounted over LM guide(linear motion) up and down wards.the motion has to be quite smooth and the whole setup shld be very compact.

so i had stepper motor at first in mind.but to get smooth motion it shld run it in micro stepping mode.and stepper also need huge power supply.
next is simple dc motor.a medium sized motor from printers.which works on 12v@200-500ma.( http://www.pcgadgets.com/DC%20motor.jpg )

now the problem is,i need very low rpm with moderate torque(shld be able to pull plate).this i can do in stepper.but i don't know how using dc motor.
driving the dc motor using PWM will give me good torque(moderate) with low rpm?

I need some desperate help here
Regards

 

[Ubergeek63]

depends on how accurate a control you want... if absolute accuracy is not an issue get a gear motor.

 

[didimus]

Go with a stepper motor It will be much simpler to control it. It may require more eletronics ( maybe even not!) but it will pay off when cotrolling.

 

[fever]

accuracy i do need some.the mounting plate has to move with predefined speed.say 1.5inch in 5 sec.the imp thing here is smoothness in the motion.it shld not be distorted.
so isn't possible using a dc motor with PWM driver?

 

[Ubergeek63]

accuracy i do need some.the mounting plate has to move with predefined speed.say 1.5inch in 5 sec.the imp thing here is smoothness in the motion.it shld not be distorted.
so isn't possible using a dc motor with PWM driver?

Yes and you also mentioned size. If all you need is approximate speed a DC gear motor would be the smallest.

perhaps something like this:
Jameco Electronics Electromechanical: VARIOUS: HN-GH-1213-24Y-70

 

[fever]

i have full resources to build the gear box separately if required(complete workshop of my friend).but i don't have much knowledge of gear ratio calculation and making of gear box.
can some one help me here?

 

[didimus]

i have full resources to build the gear box separately if required(complete workshop of my friend).but i don't have much knowledge of gear ratio calculation and making of gear box.
can some one help me here?

You can get it from the number of teeth or the radius (which are proportional). I am a radius guy so let´s say one hae gear 1 and gear 2.
And that the angular speed of them are w1 and w2, respectively.
same for the radius, r1 and r2 and so on.

YOu can connect them two ways:
1- teeth with teeth, then the velocity on the outer will be the same and the angular speed ( w1 and w2 ) will be different by the ratio of r1.w1=r2.w2
2- both an the same shaft, then angular speed, w1 and w2, will be the same and velocity, say v1 and v2, will be different. You get them from angular speed, v1=w1.r1 and v2=w2.r2.

Keep in minde the faster you get with you gears less torque you will have.

 

[fever]

thanks for the response guys.
@didimus thanks for the technical explanation.

i was doing some search for diy gears.and found that, using the wiper motor will serve my purpose correctly.
if i ran it at 12v the output rpm is 40-50.i can get reduced rpm either by lowering the voltage or by using PWM circuit.
the best thing abt these they are available every where and cheap to.
what do u guys think abt it.