Motor setup advice

Discussion in 'Electrical Forum discussion & Blog' started by joeyar, Jan 10, 2008.

  1. joeyar

    joeyar New Member

    Messages:
    5
    I am designing a turntable which will be used to spin plants to demonstrate to first year university students that they will grow towards the axis of revolution.

    To do this I need a motor. I have decided to go with a three-phase AC induction motor, and with it I am going to get a VFD (variable frequency drive). I will be using a fan-belt drive.

    My question is: am I going to have to adjust the diameter of the shaft of the turntable in my design in order to cater for the difference in speed (rpm) of the motor and the speed I want the turntable to rotate at (49 rpm), despite the VFD or will having the VFD mean I don't have to worry about that too much? That is one thing I am stuck on at the moment.

    Any help on this matter would be much appreciated. Thank you.
  2. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Why not employ an old record changer as a drive? You get 45 rpm that way, and at very little expense.
  3. joeyar

    joeyar New Member

    Messages:
    5
    I'm not convinced that would last long enough .... a record changer drive is not really designed for continuous running for hopefully (knock on wood) 10 years + .
  4. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    What motor is designed for a decade of continuous running? And what class is going to last for a decade? First year university courses must have changed since I was wasting time at college.
  5. joeyar

    joeyar New Member

    Messages:
    5
    Certainly I am convinced there are motors that will last a lot longer than an old record changer.

    It's a basic physics course. It's for a New Zealand university, not an American college. Yeah courses change but this is part of the course that's in it for the long haul.
  6. joeyar

    joeyar New Member

    Messages:
    5
    Also with plants (and thus soil) the turntable is going to be much much much heavier than the weight of a record.
  7. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Well, just as a practical approach, there must be a zillion old BSR MacDonald record changers out there with nowhere to go, and they did have reliable motors, so if the weight of the plants is not too much, you have that as an option.

    Now if you enlarge the sizes and weights beyond what a phonograph could handle, then you can still manage with simple motors and belts and pulleys. Is there an equivalent to an industrial supply house like Grainger in New Zealand?
  8. joeyar

    joeyar New Member

    Messages:
    5
    I am probably going to have to order some parts from Australia but there are a few spcialist motor stores around the joint, nothing hugely industrial.

    Yeah the motor and belts and pulleys were what I was originally going to go with but if you have any additional information I would gladly appreciate it.
  9. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Grainger is an industrial supply house where I can buy motors and belts and pulleys. If you have a platform for your experiment, you can 'conect the dots' with the appropriate belts and pulleys. I can picture a platform of wood, with a groove notched into the edge, for taking the belt. It wouldn't take a fancy motor to make this work, and you can still look at how a belt-driven phonograph turntable works, as a guide to building your project.
  10. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Well, since this is a plumbing forum, I can relate about the reactor main coolant pumps on submarines. When GE or someone was designing those pumps and motors, they asked Rickover what he would spec for longevity and pump seal leak rate. He said 20 years and zero ounces leakage over the 20 years. First they fainted, but then they did produce the design. I guess the price tag was a million or so each, in 1955 dollars!
  11. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Good 'ol Mil Spec!! Yee-haww!
  12. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,713
    Location:
    Central Florida
    don't forget they had to run dead quiet, too, I'll bet.
  13. alternety

    alternety Like an engineer

    Messages:
    650
    Location:
    Washington
    A VFD motor is real economic overkill for a fixed rate application. Actually even a variable speed application in the right circumstances.

    Get standard motor with sufficient power to turn the mass of the platform and contents. You might want to think about start up acceleration/deceleration/motor stalling when you service/add/remove the plants.

    Build the platform. Pully on support shaft. Pully on motor mounted under the platform. Belt between them. See a book for diameters.

    Protect the motor/belt/bearings from nasty stuff associated with growing plants. Use good bearings and support for the shaft/platform.

    Simple. If the motor breaks, it is a standard motor and you just replace it.

    An alternate to a simple constant speed AC motor would be a DC motor (preferably a permanent magnet version). These have nice smooth torque characteristics and can be made speed adjustable and soft start/stop with inexpensive variable voltage line connected DC controllers. I am running a 1.5 HP motor from a Baldor BC140 controller. Look at the specs on that. Other people make them also.
  14. leejosepho

    leejosepho DIY scratch-pad engineer

    A large pulley on the turntable shaft would be driven by a small pulley on the motor shaft, and the ratio would be dependent upon the rpm of the motor. A typical 1725 rpm motor and something like a 43:1 ratio would net 40 rpm at the turntable. A 2-inch pully on the motor would have a circumference of about 6 inches, and that would match to a turntable pulley of about 82 inches to end up with 40 rpm. If you do not want a turntable that large, a simple gear motor could be used to reduce the speed of the drive pulley and allow for a smaller driven pulley. Or, a small lawnmower transmission could be used ...
    Last edited: Jan 11, 2008
  15. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,713
    Location:
    Central Florida
    The power required to keep the thing turning will be very small if the turntable is balanced and mounted on a single ball bearing, like the old high-quality record turntables were. Startup power required will depend on the total mass, of course, but you could use a separate motor (or a graduate student) to provide that impetus.
  16. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    I did that as an experiment as a kid to see if grass would go straight or at an angle, I used an old record player as the spinning device.
  17. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,713
    Location:
    Central Florida
    Well? Don't keep us in suspense...
  18. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    I don't remember that was over 20 years ago...:D
  19. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    I would use the motor shaft as the drive pulley and turn a groove in the edge of a piece of plywood or MDF as the driven pulley. If you want a larger drive pulley you can put a piece of plastic on the shaft, use the motor as a lathe, and use a rasp to cut a groove in it.

    If you get a round belt you can take an extra turn around the motor shaft for more torque.
  20. HandyAndy

    HandyAndy General Contractor, Farmer

    Messages:
    68
    Location:
    Haxtun, CO
    you could probly jsut use a gear motor, and get very close to the 45 rpm you want, regardless there will probly be some maintenance on the item over the years, bearings and possibly a few motors, (If you can find some surplus motors, you could buy a few if the price is right and jsut set them back for spares), or set it up with a double reduction pulley system, and spring load the pulleys or the tightener, so the tension is automatic,
Similar Threads: Motor setup
Forum Title Date
Electrical Forum discussion & Blog measuring blower motor current Sep 10, 2013
Electrical Forum discussion & Blog Slowing a Capacitor-Start pump motor Jun 8, 2012
Electrical Forum discussion & Blog Conversion of 220 blower motor to 110 May 31, 2012
Electrical Forum discussion & Blog Grounding Whirlpool Tub Motor and Heater - Bonding Panel to Electric Water Heater Feb 5, 2012
Electrical Forum discussion & Blog Blower Motor Control Oct 30, 2011

Share This Page