servo or DC motor

bbrown · Sep 23, 2004

I,m working on my capstone project (an operational model drawbridge, PLC controlled), and don't know wether to use a servo to lift the bridge or a motor. are there special modules needed to control a servo? our PLCs at school are basic with 12 inputs and 8 outputs, no additional modules (Allen Bradely somethings, trainer boxes)

any and all help would be greatly appreciated.

Ben Brown

RussB · Sep 23, 2004

Servo or DC Motor

If it was mine, I would use a 3 phase motor and a VFD.

bbrown · Sep 23, 2004

did you miss the part that said "model" drawbridge? I don't have access to a three-phase source inside the classroom/lab nor do I want to build the bridge to that scale.

thanks for the response tho

Ben Brown

Ken Moore · Sep 23, 2004

I think that as long as it takes some about of time to raise and lower the bridge, say 10-30 seconds, you should be able to use a standard motor and limit switches.

Ken

bbrown · Sep 23, 2004

Ken, I am leaning towards to motor side, but would have to find a gear reduction in the scale that I want to turn at about 1 rpm. I just didn't know if a servo would be better suited for the job.

electrified3 · Sep 23, 2004

In your application I would say a decent dc gear reduced motor should do the trick, only bad thing with that is you will need some type of switch's to indicate a full raised position or lowered position, you could just use a type of cam on your linkage to your bridge to the motor for this to make somewhat clean looking. Servos are great for precision control, but you pay the price for that. Better yet a self contained dc linear actuator, self contained unit, generally can get with switch's built in and a relatively cheap.
Good Luck.

rsdoran · Sep 23, 2004

Check out http://www.grainger.com, they have an abundance of DC gearmotors. One example is this 90vdc 3.2RPM gearmotor: http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611697921&ccitem=

With this type motor you can use 115vac power source and a bridge rectifier to convert to DC, doesnt have to be an expensive power supply. You can also use a potentiometer to slow down the motor if needed.

Servo in this application would be overkill, they are used for precision movements. All you need to do is go up then down.

Eugen · Sep 23, 2004

Also a single phase VFD and a single phase motor might do the trick.
But you will have to find one that can be reversible I think I've seen some (wire the proper leads out of the connection box and use a relay). Or make a reversible gear.

It MIGHT be cheaper (Or not)

ndzied1 · Sep 23, 2004

If you're on a tight budget, try this place:

http://www.sciplus.com/

bbrown · Sep 24, 2004

thanks for the info guys, Norm that web page has some great stuff.
I'm going to hit the local hobby shop after class Sat. and see if they have anything i could use, I'll need some silly little train crossing lights and bell.

I also have a question about reflective swithes. at what distance do they quit sensing, 6-12" or less? I need some sort of sensor in the control rung to verify that the bridge is clear of traffic and peds.

thanks again guys this site is great!!!!

Ben Brown

arj3090 · Sep 24, 2004

What about a stepper

Have you considered a stepped motor? Small ones can be very inexpensive and it will give you speed control and positioning. They generallu run on 24VDC.

servo or DC motor

bbrown

Member

RussB

Lifetime Supporting Member

bbrown

Member

Ken Moore

Lifetime Supporting Member

bbrown

Member

electrified3

Member

rsdoran

Lifetime Supporting Member

Eugen

Lifetime Supporting Member

ndzied1

Lifetime Supporting Member

bbrown

Member

arj3090

Guest

Similar Topics