Motor setup advice

Users who are viewing this thread

joeyar

New Member
Messages
5
Reaction score
0
Points
0
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.
 

Wet_Boots

Sprinkler Guy
Messages
799
Reaction score
2
Points
16
Location
Metro NYC
Why not employ an old record changer as a drive? You get 45 rpm that way, and at very little expense.
 

joeyar

New Member
Messages
5
Reaction score
0
Points
0
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 + .
 

Wet_Boots

Sprinkler Guy
Messages
799
Reaction score
2
Points
16
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.
 

joeyar

New Member
Messages
5
Reaction score
0
Points
0
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.
 

joeyar

New Member
Messages
5
Reaction score
0
Points
0
Also with plants (and thus soil) the turntable is going to be much much much heavier than the weight of a record.
 

Wet_Boots

Sprinkler Guy
Messages
799
Reaction score
2
Points
16
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?
 

joeyar

New Member
Messages
5
Reaction score
0
Points
0
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.
 

Wet_Boots

Sprinkler Guy
Messages
799
Reaction score
2
Points
16
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.
 

Jimbo

Plumber
Messages
8,918
Reaction score
18
Points
0
Location
San Diego, CA
What motor is designed for a decade of continuous running? .

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!
 

Alternety

Like an engineer
Messages
768
Reaction score
0
Points
16
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.
 

Leejosepho

DIY scratch-pad engineer
Messages
2,483
Reaction score
0
Points
36
Location
200 miles south of Little Rock
Website
www.nonameyet.org
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?

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:

Mikey

Aspiring Old Fart, EE, computer & networking geek
Messages
3,024
Reaction score
17
Points
38
Location
Hansville, Washington
Also with plants (and thus soil) the turntable is going to be much much much heavier than the weight of a record.
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.
 

Chris75

Electrician
Messages
607
Reaction score
0
Points
0
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.
 

Bob NH

In the Trades
Messages
3,310
Reaction score
9
Points
0
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.
 

HandyAndy

General Contractor, Farmer
Messages
68
Reaction score
0
Points
0
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,
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks