Hello,
For a stage design project, I will have to build an arduino based clothesline pulley.
The project is to motorize the pulley thanks to a stepper and I would need your help to study its feasibility.
The clothesline would be 8 meters long (25 ft) and will have to move a few coat hangers at the speed of a walking men
I have already used steppers with an arduino and an Easy driver.
But my questions here are dealing with the choice of the stepper and the mechanical design of the pulley.
Which torque will I need if I want to make the coat hangers move quite fast (with 10cm wide pulleys for instance.)
What kind of cable and what pulley material would you choose to prevent slippage?
Thank you!
Google model cable cars.
Budget?
How durable does this need to be? Super temporary...or like, every night for a few months?
1teractiv:
Hello,
For a stage design project, I will have to build an arduino based clothesline pulley.
The project is to motorize the pulley thanks to a stepper and I would need your help to study its feasibility.
The clothesline would be 8 meters long (25 ft) and will have to move a few coat hangers at the speed of a walking men
I have already used steppers with an arduino and an Easy driver.
But my questions here are dealing with the choice of the stepper and the mechanical design of the pulley.
Which torque will I need if I want to make the coat hangers move quite fast (with 10cm wide pulleys for instance.)
What kind of cable and what pulley material would you choose to prevent slippage?
Thank you!
What's the diameter of the pulley? Pi * d will give you the amount of linear movement for one revolution of the pulley, assuming no slippage. From that you can work out how fast the cable will move (RPM * Pi * d).
Speed of a walking man = 3 to 4MPH..say 3.5MPH. 3.5 * 5280 /3600 = ~5.1 feet per second.
Assuming a 4" diameter pulley and taking Pi as 3 for ease of calculation, one revolution of your pulley will move the cable ~1 foot. You need ~5 ft per second for walking speed, so 5 revs/second = 300 RPM. You'll have to experiment with the RPM to match the walking speed of your actors. 300 RPM seems a bit fast. I'd start with 150 RPM and increase it, if it's too slow.
Torque will depend more on the amount of friction in the system and the weight of the moving parts than the speed.
1ChicagoDave:
Budget?
How durable does this need to be? Super temporary...or like, every night for a few months?
Hello Chicago Dave.
It can't exceed 300$-350$.
The mechanism should be kept for ten shows this fall maybe more next year. So it is not supposed to be super temporary. We will only ajust its length to the stages we will visit in the future
Henry_Best:
What's the diameter of the pulley? Pi * d will give you the amount of linear movement for one revolution of the pulley, assuming no slippage. From that you can work out how fast the cable will move (RPM * Pi * d).
Speed of a walking man = 3 to 4MPH..say 3.5MPH. 3.5 * 5280 /3600 = ~5.1 feet per second.
Assuming a 4" diameter pulley and taking Pi as 3 for ease of calculation, one revolution of your pulley will move the cable ~1 foot. You need ~5 ft per second for walking speed, so 5 revs/second = 300 RPM. You'll have to experiment with the RPM to match the walking speed of your actors. 300 RPM seems a bit fast. I'd start with 150 RPM and increase it, if it's too slow.
Torque will depend more on the amount of friction in the system and the weight of the moving parts than the speed.
Thanks for your explanations.
3 light coat hangers will be moved, their overall weight won't exceed 1kg.
Pulleys will be machined in aluminum by a friend and bearings will decrease friction as much as possible.
Until now I have only used cheap steppers with small stall torque and low speed.
So, I wish I could find a strong stepper, even with specs beyond my needs, and not to worry about its capabilities.
would you have an idea of the stepper I could pick to use with the big easy driver?
Do you think 3 Nm cnc machine steppers will do the job?
Thanks again
Unless you want to position the "clothesline" precisely I can't see any need for stepper motors.
Is the clothesline a continuous loop over a pulley at each side of the stage so that all the forces for keeping the line taut are taken by the pulley mountings and the motor is only concerned with moving the line too and fro? In that case if the pulleys have good bearings it probably won't require much force to move the line. I would try a cheap DC motor with reduction gears. The advantage of this is that the Arduino analogWrite() instruction can be used to control the speed.
On the other hand if the motor is required to maintain tension in the line it will have a very heavy load on it.
...R
You don't seem to be asking for very high speed or force.
I would suggest you start by building the 'clothesline' part from ordinary hardware store components such as cord and a couple of pulleys. This sort of thing is commonly available to make ordinary clotheslines and I would go for a simple rugged existing solution. This means that whatever else happens, the thing isn't going to physically drop on your head.
Your next problem is to drive it. I'd suggest using a DC motor and gearbox with a large reduction, and a friction wheel that presses against the outer face of the pulley. There will have to be some trial and error here since you will need to find out how much force is needed to move the line, and what speed works for you, and what size motor and what gear ratio you need to produce that. As a starting point, if your pulley system is fairly free moving and you only a few ounces to move it, you might get away with a 10W motor and about a 100:1 reduction. It is possible to get small DC motors with integral gear boxes for a few quid / bucks / dollars and that may be all you need. I'd suggest you get something that has the capability to move faster than you need, and then control the speed using PWM. I wouldn't bother trying to measure the speed and provide any sort of feedback control unless the resistance of your pulley system is changing a lot, and I don't see why it would be.
Ok, thanks robin and Peter.
I will try to use a dc motor and make some experiments.
As robin said, the clothesline will be a closed loop between a pulley at each end of the scene.
My cable should be as tight as possible to avoid the sagging.
I hope it won't increase the motor effort to much
the good idea is the friction wheel to make the cable stuck to the pulley.
Should I also pick some pulley with an inner rubber material to help the cable follow the rotation?
Versatile mounting and output connections, high output torque, easy drive, low cost and availability make automotive motors such as wiper, window regulator, seat adjusters, etc., possible solutions for many projects. - Scotty
1teractiv:
the good idea is the friction wheel to make the cable stuck to the pulley.
Should I also pick some pulley with an inner rubber material to help the cable follow the rotation?
I would not expect any problem with the cord/cable slipping on the pulley. The only place where you might have an issue is slip between the motor/gearbox output and the pulley. I've suggested using a friction drive here for simplicity, and that could be as simple as a rubber tyre/band on the outside of the driven wheel.