Advice selecting motor for drum winch and pulley system.

Using Arduino Motors, Mechanics, Power and CNC
#1

I am trying to make a drum winch for an art piece that slowly lifts and raises a curtain - I have attached a simple image.

The movement of the curtain will be defined using Ultrasonic sensors to detect when the curtain is nearing the top or bottom of its range. The curtain should be moving all the time, but slowly.

The drum winch will form the base of a rotating structure that weighs approximately 3kg. The weight of the curtain is a maximum of 1.5kg.

The distance will be defined by the sensors so the motor doesn't need to be that accurate but it does need to be as quiet as possible (some sound is fine). The servo motors I have tried have been quite loud. I was thinking a geared DC motor might be better?

I'm fairly new to using motors and unsure of the best type to use.

Also would I need to incorporate an automatic break?

Any help would be greatly appreciated. Thank you in advance!

nb: I have seen a similar question here (), although I think my requirements might be different since the motor itself doesn't need to be particularly accurate, just slow and quiet.

#2

There was a problem with the attachment - I have reattached.

IMG_4900a.jpg|1000x750

#3

Hi, Maybe a car electric window motor. 12VDC and easily PWM speed controlled. About the right RPM?? Like these:

On Amazon, Rockauto.com, many others, or your local junkyard (Oops, sorry, "Professional Auto Dismantler")

#4

Several years ago I fabricated a portable crane to lift the solder pot out of our selective solder machine. Runs off a 12 volt storage battery which is also used for ballast. Somewhere there is a picture! The 12 volt motor I found to drive it up and down it from the cable driven slide-out mechanism from a recreational vehicle(RV). It is worm gear driven, right angle output shaft, so a brake is not needed. The motor came from EBAY. You may be able to find something similar.

The cable mechanism for the RV industry did not work well because the cables were long and would stretch unevenly and cock the slideout.

Paul

crane.jpg|604x453

#5

rvmunrokerr: The distance will be defined by the sensors so the motor doesn't need to be that accurate but it does need to be as quiet as possible (some sound is fine). The servo motors I have tried have been quite loud. I was thinking a geared DC motor might be better?

Steppers are loud, spur-gears are loud. I vote for the worm-drive option as fairly quiet, or a belt-drive.

You need to provide the radius or diameter of the drum, some indication of kind of rope/wire and pulleys you plan to use - then a better idea of necessary torque can be figured out.

How fast does the curtain need to move?

#6

Ultrasonic distance sensors are not particularly reliable and WILL lead to malfunctions. The Arduino might also malfunction.

I would use simple electrical limit switches as sensors instead, with a safety backup system that will interrupt the motor current if the curtain is moved beyond additional hard limits.

#7

Your diagram of the cables will not work. Looks like the cable on the left side is fastened to the cable on the right side. As soon as the fastened position is moved, the curtain will be twisted.

Paul

#8

A worm drive has the attraction that the load cannot turn the motor so you can safely turn off the motor and the load will stay where it is.

...R

#9

Thank you everyone for your answers. They're very helpful!

Paul_KD7HB: Your diagram of the cables will not work. Looks like the cable on the left side is fastened to the cable on the right side. As soon as the fastened position is moved, the curtain will be twisted.

Paul

Yes, sorry about that - it's my poor drawing. It'll be two separate lines (one from each end) that feed into the same pulley block.

MarkT: You need to provide the radius or diameter of the drum, some indication of kind of rope/wire and pulleys you plan to use - then a better idea of necessary torque can be figured out.

How fast does the curtain need to move?

Drum diameter = 0.60m.

There will four pulleys in total - one at each end of the curtain. One to feed the line downwards and one to feed the line onto the drum.

Would there be a difference in using wire and rope, apart from stretch?

The curtain should move slowly. I'd estimate around 0.005 or 0.010m per second. Exact speed isn't crucial. It should just be 'slow'.

jremington: Ultrasonic distance sensors are not particularly reliable and WILL lead to malfunctions. The Arduino might also malfunction.

I would use simple electrical limit switches as sensors instead, with a safety backup system that will interrupt the motor current if the curtain is moved beyond additional hard limits.

Do you mean Ultrasonic sensors are unreliable in that they will give some inaccurate readings or in that they will break after time?

Limit switches are a good suggestion.

Worm gears it is then. I will investigate further. Thank you for your help!

Rosie

#10

Do you mean Ultrasonic sensors are unreliable in that they will give some inaccurate readings or in that they will break after time?

Both, but most often they will give very inaccurate readings.

#11

Cable example for consideration. My crane must lift 40 lbs. The cable is 1/16 inch steel cable. Rated at 90 lbs. So, you can convert that to metric can find the equivalent in your area. I am sure your curtain is lighter than 90 lbs.

Paul

#12

So a load of 15N (plus friction), on a drum of radius 0.3m, gives a torque requirement of 4.5Nm, plus a good margin to overcome friction, say 8Nm as a working figure for the drum. Velocity of 0.01m/s translates to angular velocity of 0.033 rad/s.

power = torque x angular velocity = 8 x 0.033 = 0.26W

This is a tiny load, but massive gear reduction is needed (typical small motors run at 500 rad/s (5000rpm)), perhaps 15,000:1

That also suggests worm drive (big reduction ratio in one step), driven from a 100:1 gear motor or so, or a belt drive from a 1000:1 motor

It makes more sense to talk about the rpm of the gear motor really - lets say you can find a 30rpm motor, which is about 3 rad/s, then a 100:1 worm reduction from that.

You can also choose a more power motor and run it slower than its full rating to get slower than rated speed (0.26W is miniscule for a motor, using a 5W motor and running at 5 to 10% speed is more plausible).

The other drive technique that might be good for this sort of reduction is friction-drive to the rim of the drum, using a thin spindle - that might give 100:1 or better in one step, and probably has enough friction to prevent back-driving from the curtain weight.

A gear-reduced stepper motor is another possibility, very slow speeds are easy then as you progress step-by-step.

#13

Thank you for your responses - very helpful and have lots of experiments to be getting on with!

#14

Hello again.

I have a question about power supplies for this motor.

The car window motor I have been looking at has the following specs.

Stall current: <28A at 12V Rated current(load): 15A Current(No Load): < 5A

Would I would need a power supply rated up to 28A?

Would something like this be suitable, rated to 30A?: http://ebay.eu/2iYGdzZ

Thank you

#15

You can use a less powerful supply, but be aware it then has to handle overload gracefully (during start up and other stall conditions). If it were to shutdown on overload, you'll just get it repeatedly pulsing and doing nothing useful. This can be helped by ramping up PWM drive to the motor so that stall current doesn't have to flow.

However I am having trouble understanding why you are looking at such a powerful motor for moving a 1kg load at 1cm/s...