ry_pi
Posts: 2
Joined: Mon Jun 24, 2019 4:10 pm

Motor for Pulley System

Mon Jun 24, 2019 7:41 pm

Hi All,

Long time lurker, first-time poster here.

I am looking for some guidance/advice on how to pull a set of grow lights with a motor controlled by my Raspberry Pi 3 B+.

The idea here is to utilize an ultrasonic distance sensor attached to the light ballast to gauge the height of the lights above the plants. If the height is less than 15 inches, then activate the motor for X seconds to pull the lights up. I am assuming here that the motor will move at a constant pace so I can get a gauge of how many inches per second the motor will pull the lights and then run it for a set amount of time to move the lights a prescribed distance each time the plant gets within 15 inches of the ultrasonic sensor.

First, there are a few things that I will need to be able to do.
1. The motor must be strong enough to pull the lights (estimated 15 lbs max)
2. The motor must be able to pull the lights a total distance of 4 feet
3. The motor must not drop the lights after pulling them up

My dilemma here is that I am so inexperienced in this realm I simply do not know what the best way to do this would be. My initial thoughts on this were that I just need some sort of winch that will pull up the lights when I activate it with the Raspberry Pi, but I have so far been unable to find something exactly like this.

After some research, I have begun looking at using a Linear Actuator along with a pulley system to pull the lights, similar to the attached image. This motor would be strong enough to lift the lights, would not drop the lights after pulling them, but may not be able to pull the entire 4 feet I need them to move as the longest range I've found is 18 inches. Of course, my gut instinct is there is a way to account for this as my fishing reel does a 4:1 rotation allowing me to reel in 4Xs the line I would normally with just a 1:1 rotation but not sure how I can apply this to pulling up my lights.

The other option I was looking at would be using something like a window motor, or a worm motor, as these seem to have the power to pull up the lights, the resistance to not drop them, and the capability to pull them the entire 4 feet. The problem here for me is I am having trouble understanding how I'd create a winch with this sort of system.

Lastly, I've seen mention of NEMA motors, but these don't seem like they have enough torque to pull the 15 pounds.

Any advice/suggestions for this would be greatly appreciated!
Attachments
Linear_Actuator_lifting_pulley_cable.jpg
Linear_Actuator_lifting_pulley_cable.jpg (107.98 KiB) Viewed 246 times

User avatar
rpdom
Posts: 14432
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Motor for Pulley System

Tue Jun 25, 2019 5:35 am

Just some observations.

The lights also must not drop in case of power failure, or a problem with the Pi. A worm drive motor would work for this.

You should have some limit switches, so that if the lights hit the top or bottom of the runners they will stop and possibly alert you.

ry_pi
Posts: 2
Joined: Mon Jun 24, 2019 4:10 pm

Re: Motor for Pulley System

Tue Jun 25, 2019 2:08 pm

Great point. I definitely do not want a power outage to crash my lights, nor have them crash too high. I have a few door sensors that I believe could be utilized to prevent the motor from pulling too much and think that the ratcheting system on some pulleys I found online would prevent them from collapsing.

I did a bit broader research into this subject of moving large items with Raspberry Pi / Arduino last night and have been turned onto another possible solution using ratcheting pulleys, a motor attached to two pulleys with a timing belt, and a spool. I have attached a quick sketch I put together of what the system would look like and believe this may be my best bet given the lower cost than a linear actuator and the detailed guide I can follow on youtube.

Going to continue doing more research to confirm exactly how this will work out and would appreciate any input from those who may have experience creating something similar.

https://youtu.be/kaJVWoKj2a4?t=90
Attachments
Light Pulley System Sketch.png
Light Pulley System Sketch.png (165.55 KiB) Viewed 196 times

Return to “Automation, sensing and robotics”