Mechanical Design Assistance???

OK, I wanted to drop this here just for consistency. Hopefully folks will get notifications and check it out.

I think I've worked out the my rotator design. If the motor mcb1 recommended works then that drops the price from $30 + controller board to $6 for the motor and controller board. Thanks mcb1!

Just as a side note: I've found less expensive LED grow light bars as well. I love it when the price of a project goes down.

Here's my design for the rotator. All this will be in the updated detailed design document on my next blog post.

A little explanation... The 1/4" X 10" plywood disk will have standard GT2 6mm timing belt inverted and fastened to the outer edge. This will form a timing gear if you will. The timing pulley on the stepper will be pressed up against the "timing" disk. Who knows, maybe it'll work? I've calculated that around 40,000 pulses will rotate the turntable once. Honestly, I don't know what would be optimum but just for the sake of argument let's say 4 revulotuins per day. That's 160,000 pulses per day/86,400 sec = 1.9 pulses per sec.  I think the MCU will handle that, no matter how I may decide to split all that up. My main concerne is that the whole system is stable enough so that the gear and pulley remain in contact all the time. The Lazy Susan bearings are rated at 750lbs so it should be plenty stable. But getting the timing disk and Lazy Susan bearings centered to each other is super critical, so we'll see. If not then I have a backup plan to move the motor back and use an actual tensioned timing belt around the timing disk and pulley. I just want to see my wonky inverted timing disk work though.

Thanks for the input Enrico.

The drawing in my post is based on a beltless design. The timing gear and pulley are actually in contact with each other. But I don't know if I can build the mechanism accurately enough to achieve that. So, there's a backup plan to slide the motor back a few inches and incorporate a belt. In that case, I will definitely take your advice. I have already located the parts for a small tensioning system. A single small timing pulley and a tensioner spring should do the trick.

Cheers,

Rick

Hi Rick,

thank you for the answer. The reason I will use in a case like this a timing belt is for the smooth moving respect the direct traction, always speaking of very slow moving. Anyway, if it is helpful for you I attach an image showing how I have applied the timing belt solution, in a very cheap way.

Just another question: how is done the mechanics of the rotating base? To you use a central axis with a ball bearing or a recirculating ball bearing? I suppose that the rotating base should support a considerable weight.

Cheers, Enrico.

Thanks Enrico.

Is that tension pulley spring loaded?

I have attached a picture of the lazy Susan bearing. It's rated at 750lbs so it should more than do the job. I'm expecting the fully loaded tower to be no more than 40 to 50 pounds.

Hi Rick, I had to reread about the lazy Susan bearing. As a matter of fact I discovered that I have done the same for a camera rotation base. But I had not idea of what was the name I attach here a picture just to explain what I mean. The principle is the same and testing it I saw that is very good for stability and weight support. In my case it was smaller and more precise but the principle it is almost the same.

Instead the push pulley is not with tension. I have read - before buying - then directly tested that as a matter of fact the timing belts are almost like gears with very few flexibility and they didn't tend to loose their tension in time. So after placing the engine and the belt, the pulley is adjusted for the right pressure then the axis is locked with a self-locking nut.

Wow... You put together your own bearing. That's just cool. I wish I had time and the mobility to do that. But, for this project I am using off-the-shelf parts for just about everything. Except for a couple of mods here and there.

For the beltless design my only concern with the timing belt is this. I am going to be stretching the belt backwards around the diameter of the 10" disk. I know this will stretch the teeth of the belt apart by some degree. I hope that the 2mm pitch pulley still engages the belt teeth correctly. If not I may have to increase the pitch of the pulley.

In the belted design I think that the timing belt will mesh correctly with the disk belt because it will be somewhat flexible.

The belt is few flexible but not so much to create a serious difference between two teeth so I think it is almost meaningless for the movement. Obviously all depends on how much do you need to stretch the belt. But in theory your disk perimeter should be a multiple of the teeth spacing, +/- 1/10 teeth. In my opinion you should try and if it is the case you can lathe very few the disk circumference just to reduce the stretching. I have no idea of what kind of timing belt you are using and the teeth step (the distance between two teeth). Take in account that the shaft gear and the belt gear are not perfectly angular as the physics of the movements transforms a linear movement in rotational movement; to maintain a continuous contact between the two teeth series the gear is rounded, not perfectly angular.

If you can give me some more information on the kind of belt maybe we can check but the most important parameter is the distance you should stretch the two belt ends.

Enrico

Rick, the relationship for rotations, or revolutions is gear ratio. For example, if you want 4 rotations of your cultivator per day that means you want ONE rotation every SIX hours, 1/2 rotation every 3 hours or 1/4 rotation every 1.5 hours. Normally you would want a gear ratio between your cultivator base size and your motors pulley size. However, since you're going to use stepper motors,  all you should need to do software-wise is make use of timing parameters to step the turntable once every 6 hours. Using wait, if/the, for, or pause commands or some other variable to reference the passing of time should work for you. For example is you want it to turn 1/4 turn, have it 'sleep for 5400 seconds (3600 secs/hr * 1.5 hrs=5400 seconds). Do that 16 times via an "if' or "while' type statements and your turntable will rotate 4 times in a 24 hour period. It's all about the math!

Thanks for the info Michael...

I think I have it worked out now. The control application will just be a simple state machine based on "the big loop". Reading sensors, performing control functions and logging them, via the radio, back to the central control/monitor system. I think control functions and reading the sensors should be very lightweight. There's no sensor that needs to be read more than once a second, and that's probably overkill. As the EZR32WG has some very low power modes available I plan to have it sleep most of the time and wake up only periodically to run the loop. The central control/monitor will have the ability to wake the crowing area system up at any time and instruct it to read sensors and/or perform control functions.

I'll have to workout all the timing and pulse count once I have the MCU in hand and the rotator is completed. So far my calculations go like this... My stepper motor is geared and requires 4096 pulses per revolution. There is about a 10:1 ration between the timing gear, at the turntable, and timing pulley on the stepper motor. That gives me about 41,000 pulses per revolution at the turntable. If I want 4 revolutions per day so that's 164,000 pulses per day. That works out to about 2 pulses per second. So I could just pulse it a couple of times on each wake up cycle. Since the motor is geared it doesn't require power to remain stationary. We'll see.

Right now I'm waiting on the final parts for the turntable and on the E14 kit. It's all just theory right now. lol...